CNS – lab session

Historical figures

Prior to the 18th century, the nervous tissue was thought to be functionally like a gland. It was said that nerves conveyed fluid, which was secreted by the brain and spinal cord to the body periphery.

Below is a list of individuals whose accomplishments helped to shape the current understanding of the CNS:

Camillo Golgi (1843-1926)

Golgi developed a way of staining neurons with sliver salts and in doing so, revealed their entire structure under the microscope.

Camillo Golgi (1843-1926)

Both Golgi and Cajal won the Nobel Award for physiology and medicine in 1906.

Santiago Ramón y Cajal (1852-1934)

He stained individual cells showing that the nervous system is not on continuous web but rather a network of discreet cells. Using the histology techniques developed by Golgi, Cajal developed the “Neuron Doctrin”, which states the following “that individual neurons are the elementary signalling elements of the nervous system”.

Santiago Ramón y Cajal (1852-1934).

Both Golgi and Cajal won the Nobel Award for physiology and medicine in 1906.

Ross Harrison (1870-1959)

Demonstrated that two major projections grew out of the nerve cells: the axons and the den drites. He was also able to confirm that the top of the axons give rise to an expansion called the growth cone which leads it to its target site.

Luigi Galvani (1737-1798)

Was able to discover that muscle and nerve cells produce electricity. Modern electrophysiology grew out of work in the nineteenth century.

John Newport Langley (1852-1925)

Discovered the fact that drug interactions with animal cells is not arbitrary, but rather the drug’s molecular components bind to specific receptors on the surface of the cells. This discovery formed the basis of the important study of the chemical communication between nerve cells.

Franz Joseph Gall (1758-1928)

Was an acclaimed neuroanatomist who pioneered research into the localization of functions of the brain. He postulated 3 main principles as follows:

  • He advocated that behaviour emanated from the brain.
  • He Argued that particular regions of the cerebral cortex controlled specific function.
  • He Stated the centre for each mental function grew with use.

He pioneered the study of the pattern of the bumps and ridges on the skull which were characterized as individual areas. This disciple was named phrenology.

Marie Jean Pierre Flourens

Flouren was a physiologist who systematically lesionning parts of the brain (he preferred working on rabbits and pigeons), and then observing the effects on motricity, sensibility, and behaviour. He was particularly interested in Franz Joseph Gall’s “functional centres”, which were proposed by Gall and stated that different parts of the brain had different fuctions. By observing the animal’s reaction to the lesions he was able to prove Gall’s theory scientifically.

It was Napoleon Bonaparte who asked Flouren’s to scientifically investigate Gall’s hypothesis.

Karl Wernicke (1848-1905)

A Polish physician and antomist who discovered that individual neurons are the signalling units of the brain and so they are generally arranged in functional groups and connect to one another in a precise fashion.

General anatomical terms of the nervous system

The nervous system is built of nerve cells consisting of neurons and their supporting cells called glia. The neurons are responsible for the reception, transmission and processing of stimuli, the triggering of certain cell activities, and the release of neurotransmitters.

Each neuron consists of two parts:

The Cell body (soma) or perikaryon is the part of the neuron that contains the nucleus and its surrounding cytoplasm. The following are important facts of the cell body:

  • Most nerve cells have a spherical, large, euchromatic nucleus with a prominent nucleolus.
  • The cell body contains a highly developed rough ER and numerous free and bound ribosomes.
  • Under the light microscope, the rough ER and free ribosomes appear as basophilic granular areas called Nissl bodies.

The processes (branches) have fibres of two types:

Dendrites (afferent process = proximal process), the following are key characteristics of dendrites:

  • They are specialized for receiving stimuli from the environment, sensory epithelial cells or other neurons.
  • They are usually short and divide like the branches of a tree. Most neurons have numerous dendrites, which considerably increase the receptive area of a cell.
  • The arborisation (or high number of branching) of dendrites makes it possible for one neuron to receive and integrate a great number of axon terminals from other nerve cells.

Axon (efferent process = distal process). The following are key characteristics of axons:

  • Are a single process specialized for generating or conducting nerve impulses to other cells (nerve, muscle or gland cells).
  • Axons may also receive information from other neurons. This information mainly modifies the transmission of action potentials to other neurons.
  • The distal portion of the axon is usually branched and constitutes the terminal arborization.
  • Each branch of this arborization terminates on the next cell at the end bulbs (boutons), which interact with other neurons, or non-nerve cells, forming structures called synapses.
  • Most neurons have only one axon; and very few have no axon at all.
  • Axons may be short, or very long.

In neurons that give rise to a myelinated axon, the unmyelinated portion of the axon between the cell body and the first myelinated segment, is called the initial segment.   This is the site where various inhibitory and excitatory stimuli.

The Resting Potential.

Use of an electrode to record electrical charge from the inside and outside of the cell membrane when no current is being applied to the axon provides a measure of what is known as the resting potential which is generally around -70 millivolts.

The resting potential arises from differences in the concentration of 4 ions:

  • Sodium ions (Na+) (extracellular)
  • Chloride ions (Cl-) (extracellular)
  • Potassium ions (K+) (intracellular)
  • Large protein anions (A-) (intracellular)

Potassium: offsets the negative charge resulting from the K+.  There is a ratio of 20:1 intracellular to extracellular concentration of K+. 

Sodium: tends to be concentrated in the extracellular fluid.  There is an active pump (the sodium/potassium pump) that maintains the relative differences in the concentration of Na+ and K+ in the intracellular and extracellular fluid. The protein pump exchanges 2 extracellular K+ particles for 3 intracellular Na+ particles.

Chloride:  can move freely across the cell membrane, but its voltage gradient is similar to the membrane’s resting potential, so Cl- does not tend to contribute to the resting potential.

Demonstration of Action Potential within the cell membrane.

Changes in the Resting Potential (hyperpolarization & depolarization).

Hyperpolarization:  Applying a negative current causes an increase in the negative voltage and drives the resting potential further into the negative direction or hyperpolarization.  Hyperpolarization results from an efflux of K+ and an influx of Cl-.

The Action Potential or Depolarization occurs, the neuronal membrane changes permeability and the proteins allow for the opening of voltage-sensitive Na+ and K+ channels.  This results from the influx of Na+ into the cell and K+ out of the cell.  This change in current travels down the axon and is known as the Action Potential.

Refractory Periods:  this occurs while the axon is depolarized and means that another action potential cannot occur until repolarization of the membrane potential.

Mechanism of Action Potential.

In the CNS nerve cell bodies are present only in the grey matter, thus they are referred to as grey matter and are located as:

  • Nuclei or ganglia
  • Cortex

White matter contains neuronal processes but no neuronal cell bodies.

In the PNS – cell bodies are found in ganglia. They are located as:

  • Somatic ganglia (only sensory)
  • Autonomic ganglia of two types:
    • Sympathetic ganglia
    • Parasympathetic ganglia

Unipolar neurons have a single process that comes out of the  cell body, which is the axon.

Bipolar neurons have two processes: one axon and one dendrite (e.g. in retina of the eye).

Pseudounipolar neurons have single process that comes out of the cell body and then divides into two branches : One branch-the dendrite extends to a peripheral nerve ending and the other-the axon which extends towards the central nervous system (e.g. sensory neuron of somatic ganglia).

Multipolar projection neurons have one axon and many dendrites. It is the most common type of neuron (e.g. tract cell).

Most neurons of the body are multipolar. Bipolar neurons are found in the ear, retina and olfactory mucosa, while pseudounipolar neurons are found in the spinal ganglia (dorsal root ganglia).


Picture demonstrating the differences between a) unipolar and b) bipolar neurons.

Association neurons or interneurons form the connecting link between the afferent and efferent neurons. They have short dendrites and may have either a short or long axon.

Projection neurons are tract neurons or cells.

Commissural neurons connect and cross at the midline.

Sensory or afferent neurons – transmit afferent impulses to the CNS. They relay sensory information from skin, muscles, viscera and special senses.

Motor or efferent neurons – deliver efferent information from CNS to other parts of the body & activate effectors. They relay motor information to the muscles.

Interneuron (local circuit neuron) help co-ordinate, modify and integrate information between sensory and motor components. They form circuits and they are found only in the CNS.

Golgi type I neurons have long axons (e.g. the longest one extends from the cerebral cortex to the tip of the cauda).

Golgi type II neurons have short axons.

Isodendritic neurons issue straight dendrites, which run in all directions.

Allodendritic neurons are distinguished by shorter, branched dendrites, which are restricted in their wavy course.

Idiodendritic neurons have a unique dendritic tree characteristic determined by their location.

Myelinated fibres are white in appearance and therefore are usually referred to as “white fibres”, and are present in the “white matter” of the brain. Mylein sheaths primarily insulate the axon, and are present only in the PNS, with the primary goal of accelerating the transmission of nerve impulses.

Unmyelinated fibres are commonly referred to as “grey fibres”. There is no insulation present along the axon and the electrical impulses are conducted in a continuous “wave like” manner.

Clinnical comments:

In multiple sclerosis microglia phagocytose and degrade myelin surrounding the axons of the CNS neurons.

Astrocytes are characterized by their star-like appearance.

There are two types of astrocytes:

  • Protoplasmic astrocytes (gray matter)
  • Fibrous astrocytes (white matter)

Protoplasmic and fibrous astrocytes are found in grey and white matter respectively. Some astrocytes lay adjacent to the pia mater, where their pedicle-shaped processes contacts the pia, and forms the pia-glial membrane. Other astrocytes develop processes with expanded end-feet that are linked to endothelial cells by junctional complexes, and form a continuous barrier between the CNS and the blood vessels. This is one component of the blood-brain barrier. Additionally, they participate in controlling the ionic and chemical environment of neurons.

Notes of interest:

When the CNS is damaged, astrocytes proliferate to form scar tissue.

Picture of astrocytes present in the CNS.

Oligodendrocytes are located in both gray and white matter.  They produce the myelin sheath that provides the electrical insulation of axons in the CNS (i.e. they perform the same function in the CNS as Schwann cells do in the PNS). 

The following are examples of  oligodendroglia cells:

  • perineuronal satellite cell
  • interfascicular cell

Microglia cells are small, elongated cells with short processes, which are found in small numbers in both grey and     white matter.  They are phagocytic cells derived from mononuclear cells of the blood.  They are also involved in inflammation and repair in the CNS. 

Ependymal cells are low columnar ciliated cells that line the fluid filled cavities of the CNS. They have the morphologic and physiologic characteristics of fluid transporting cells. In the choroid plexuses of the brain, they are modified to produce cerebrospinal fluid (CSF).

  • Schwann cells in:
    • Peripheral nerve
    • Ganglion
  • Capsular (satellite) cells in:
    • Ganglion
Diagram of a mylenated schwann cell in the peripheral system.

Synapse is responsible for the unidirectional transmission of nerve impulses.

Synapses transmits information to the next cell in the circuit. 

Synapses are the sites where contact occurs between neurons and other effector cells (ie. other neurons, muscles and glands). 

Most synapses transmit the impulse by releasing neurotransmitters at the axon terminal. 

The synapse is formed by an axon terminal (presynaptic terminal) that delivers the impulse; a part of another cell (this can be the dendrite, the cell body, or the axon) where a new impulse is generated (postsynaptic terminal ); and a thin intercellular space called the synaptic cleft.

Chemical synapses are the most common synapses, which transmit nerve impulses through neurotransmitters.

  • Intracrine mediation – regulate intracellular events.
  • Autocrine mediation – substances secreted outside the cell influence the same cell.
  • Paracrine mediation – secreted substances influence adjacent cells Endocrine mediation – substances secreted into the blood vessels to act on distant target cells.
  • Ectocrine mediation – substances are released into the environment to communicate with other individuals.

Electrical synapses – a few which transmit impulses through gap junctions.

Gross subdivisions of the Nervous System

The Central Nervous System (CNS) consists of two parts:

Somatic (sensory and motor functions) part has two centres:

  • somatic nuclei
  • cortex or palium

Autonomic (visceral, splanchnic functions) part has two centres:

  • sympathetic nuclei
  • parasympathetic nuclei

The autonomic system – impulses from the CNS are first transmitted to an autonomic ganglion via one neuron; a second neuron originating in the ganglion then transmits the impulses to peripheral organs such as smooth muscles, cardiac muscles and glands.
Highly developed functions of the nervous system cannot be ascribed to simple neuronal circuits; rather they depend on complex interactions established by the integrated functions of many hundreds of neurons.

Peripheral Nervous System (PNS) consists of two types of nerves:

Somatic nerves (sensory and motor functions):

  • Cranial nerves (12 pairs).
  • Spinal nerves (31pairs).

Autonomic nerves (visceral, splanchnic functions):

  • Sympathetic nerves.
  • Parasympathetic nerves.

The brain (encephalon) consists of three primary divisions:

  • Prosencephalon (forebrain)
  • Mesencephalon (midbrain)
  • Rhombencephalon (hind brain)

During embryological development, two parts (the forebrain and the hind brain) are subdivided and finally there are five transverse segments of brain.

Spinal cord

Developmental relations of the CNS.

Prosencephalon (prosencephalon) or forebrain divides into:

Telencephalon (telencephalon seu cerebrum) or endbrain consists of two hemispheres (hemispherium cerebri): the left and right cerebral hemisphere.

Diencephalon (diencephalon) or interbrain consists of five parts:

  • Thalamus
  • Epithalamus
  • Hypothalamus
  • Subthalamus
  • Metathalamus

Clinical comments:

From the clinical point of view the concept of the brainstem (truncus encephali) is widely used.

Mesencephalon or midbrain – does not undergo any changes.

Rhombencephalon or hindbrain divides into:

  • Pons
  • Cerebellum

Myelencephalon (myelencephalon) or medulla oblongata (medulla oblongata) or bulb (bulbus).

Transverse segmentation into three & next into five gross divisions.

The brainstem consists of three following structures:

  1. Medulla oblongata
  2. Pons
  3. Mesencephalon
Illustration of the brainstem, including the pons, medulla and reticular formations.

Phylogeny the cerebral cortex divides into:

Paleocortex (“old cortex”)It is transitional cortex between archicortex and neocortex. It has 4 or 5 layers, the neurons have a nucleate-reticulate pattern. It persists as part of the rhinencephalon in the olfactory region around vallecula of the basal forebrain. The most notable example is subiculum of the parahippocampal gyrus.

Archicortex (“first cortex”) between the paleo- and neocortex. It has three layers and it occurs in the hippocampal formation. It is the inner cortex of the three concentric cerebral rings of the hemispheric walls.

Neocortex – makes up > 90% of cortex in humans (including sensory, motor, limbic and association areas). It has 6 layers has six layers and divides into:

  • Mesocortex which covers the limbic lobe (the second of the three concentric cerebral rings of the hemispheric walls).
  • Ectocortex (supralimbic cortex) which covers the most of the cerebral surface.
Phylogenetic division of the cerebral cortex.

Anatomical, clinical & functional division of the nervous system

The CNS is formed by the:

  • Brain
  • Spinal cord
  • Cerebrum
  • Diencephalon
  • Brainstem
  • Cerebellum

Notes of  Interest

We separate the brain from the spinal cord when we cut at the level of the foramen magnum across the CNS.

  • Cerebral gyri
  • Cerebral sulci
  • Cerebral lobes
  • Diencephalon
  • Mesencephalon (midbrain)
  • Pons
  • Myelencephalon (medulla oblongata or bulb)

Cranial meninges, meningeal spaces and the dural folds

The outermost meningeal layer is the dura mater (dura mater, L. dura means hard, tough and L. mater = mother). It is firmly attached to the inner periosteum of the bones except areas where there are dural venous sinuses. The dura mater consists of collagenous connective tissue. There are four margins where the cranial dura form taut connective tissue septa (the dura is duplicated) which separates and supports some parts of the brain.

The dura mater is the most superficial membrane of the CNS. It has two regional parts:

  • Cerebral dura mater
  • Spinal dura mater

The dura mater consists of two layers:

  • Outer – endostal (internal periosteum to the bones)
  • Inner – meningeal

Venous sinuses are between outer and inner layers.

The sensory innervation of the dura mater is from the CNV, CNX and CNXII and rami of spinal nerves. 

The meningeal branch of the axillary nerve supply the anterior cranial fossa, the meningeal branch of the mandibular nerve supply the main part of the middle cranial fossa, and the branch of the ophthalmic nerve supply the tentorium cerebelli. 

The meningeal branch of the hypoglossal nerve supplies the posterior cranial fossa. 

The dura mater around the foramen magnum is innervated by the CNV and the cervical nerves C1-C3.

Two of the dural septa lie in the median plane (midline) of the body (the falx cerebri and falx cerebelli).

Two other septa extend in a transverse manner through the cranial cavity.

Septa (processes) of the dura mater are divided into the following:

The falx cerebri (falx cerebri) – is in the longitudinal fissure hemispheres. The falx cerebri is a strong crescent shaped process of the dura mater descending vertically in the longitudinal fissure between the cerebral hemispheres. It is narrow in the front where it is fixed to the crista galli, and broad behind, where it blends with the tentorium cerebelli.

The anterior part is thin and perforated by numerous apertures. The convex upper margin is attached to the internal cranial surface on each side of the median plane, as far back as the internal occipital protuberance.

The superior sagittal sinus runs along this margin in the cranial groove, to both banks of which the falx is attached. Its lower edge is free and concave and contains the inferior sagittal sinus. The straight sinus runs along the falx cerebri’s attachment to the tentorium cerebri.

It has an attachment at the:

  • Crista galli of ethmoid bone
  • Inner surface of the skull cap
  • Internal protuberance and upper surface of tentorium cerebelli

Sinuses are present on the following places of the falx cerebri:

  • Upper margin – the superior sagittal sinus
  • Lower margin – the inferior sagittal sinus
  • Along the attachment of the falx cerebri – the straight sinus
The protective layers of the CNS.

The falx cerebelli (falx cerebelli) – in the sagittal plane:

It is crescent shaped and located below the tentorium cerebelli, projecting forward into the posterior cerebellar notch.

Base of the falx cerebelli is directed upwards, and is attached to the posterior part of the inferior surface of the tentorium cerebelli in the median plane.

Posterior margin is attached to the internal occipital crest, containing the occipital sinus.

The apex frequently divides into two small folds, which disappear at the sides of the foramen magnum.

It has attachment sites at the:

  • Internal protuberance and inferior surface of tentorium cerebelli
  • Internal occipital crest
  • Foramen magnum

The occipital sinus is present on the posterior margin of the falx cerebelli.

The tentorium cerebelli (tentorium cerebelli) is located in the horizontal plane between the upper surface of cerebellum and lower surface of the occipital lobe of the brain.

It has attachment sites at the:

  • Internal protuberance and lips of transverse groove of the occipital bone
  • Superior borders of the petrous part of the temporal bone /trigeminal cave/
  • Anterior clinoid processes

Sinuses are present on the following places of the tentorium cerebelli:

  • In the middle sagittal axis – the straight sinus
  • On the posterior margin – the transverse sinus
  • On the anterior margin – the superior petrous sinus (at the attachment of the tentorium cerebelli)

Free margin of the tentorium has tentorial incisura for the  midbrain.

Tentorium cerebelli divides cranial cavity into:

  • Minor cranial cave – above the tentorium cerebelli
  • Major cranial cave – below the tentorium cerebelli
The location of the tentorium cerebelli.

It extends anteriorly from the occipital bone to form a partial septum between the cerebellar hemispheres and occipital lobes of the cerebral hemispheres.

Venous sinuses are divided into the superior and inferior group of sinuses.

The superior group of sinuses totalling 6, join in the confluence of sinuses (confluens sinuum).

The superior sagittal sinus (sinus sagittalis superior) extends along the superior margin of the falx cerebri. The superior sagittal sinus on the posterior end joins the straight sinus, which connects it with the inferior sagittal sinus.

Inferior sagittal sinus (sinus sagittalis inferior) is situated along the inferior margin of the falx cerebri and drains into the straight sinus.

Straight sinus (sinus rectus) extends along the margin of attachment between the falx cerebri and tentorium cerebelli. It receives blood from the inferior sagittal sinus and great brain vein (vena cerebri magna). The union of the superior sagittal sinus and straight sinus is called the confluence of sinuses.

Transverse sinus (sinus transversus) arises from the confluence of sinuses and extends along the posterior margin of the tentorium cerebelli. It’s continuous with the sigmoid sinus at the border between the floors of the middle and posterior cranial fossae.

Sigmoid sinus (sinus sigmoideus) is S-shaped and extends through the posterior cranial fossa to the jugular foramen where it joins the superior bulb of the internal jugular vein.

Occipital sinus (sinus occipitalis) a small sinus from the falx cerebelli along the internal occipital crest. It is divided into two margin sinuses (sinuses marginales) which pass around both sides of the great foramen.

The inferior group or basal sinus (5) joins in the cavernous sinuses.

Sphenoparietal sinus (sinus sphenoparietalis) – along posterior border of lesser wings of sphenoid /communicates with ophthalmic veins / to the cavernous sinus.

Cavernous sinus (sinus cavernosus) – on each side of the body of the sphenoid bone. The left and right cavernous sinuses are connected by the intercavernous sinuses. It also communicates with the pterygoid plexus through the venous plexus of foramen ovale (plexus venosus foraminis ovalis) via the foramen ovale & internal carotid venous plexus (plexus venosus caroticus internus).

The contents of the cavernous sinus:

  • Internal carotid artery (ICA)

Into the cavernous sinus drains:

  • Superior ophthalmic vein via the superior orbital fissure &drains the orbit into the anterior part of the cavernous sinus
  • Central retinal vein
  • Sphenoparietal sinus which runs round the lesser wing of the sphenoid & pierce
  • The roof of the cavernous sinus
  • The middle cerebral vein pierces the roof of the cavernous sinus
  • Efferent veins of the cavernous sinus
  • Superior petrosal sinus which drains into the sigmoid sinus
  • Inferior petrosal sinus
Relation of the cranial nerves and arteries at the caverous sisuses (CN – cranial nerve).

Anterior and posterior intercavernous sinuses (sinus intercavernosus anterior et posterior).

Superior petrosal sinus (sinus petrosus superior) a pair of sinuses, which on each side connect the cavernous sinus with the transverse sinus. It extends along the superior margin of the petrosal part of the temporal bone. Superior petrosal sinus connects the superior & inferior group of sinuses.

Inferior petrosal sinus (sinus petrosus inferior) is paired sinus which on each side connects the cavernous sinus with the internal jugular vein.

Localisation of the sinuses and extra and intracranial anastomoses.

The arachnoid mater (arachnoidea, G. arachne, spider+eidos, resemblances a spiders web) is a delicate intermediate membrane. The arachnoid is separated from the dura mater by a film of fluid in a potential subdural space (spatium subdurale) and from the pia mater by the subarachnoid space (cavitas subarachnoideale) containing cerebrospinal fluid (CSF).

The arachnoid mater is divided into:

  • Cerebral arachnoid mater
  • Spinal arachnoid mater 

The pia mater (pia mater, L. Pius = tender) is a very thin, innermost membrane and it is highly vascularized. It adheres closely to the surface of the brain. It carries small blood vessels and when these vessels penetrate into the brain, the pia mater subsequently follows them for a short distance.

The Pia mater has two parts:

  • Cerebral pia mater
  • Spinal pia mater

Gross external anatomy of the telencephalon

Telencephalon consists of two cerebral hemispheres:

  • The left cerebral hemisphere
  • The right cerebral hemisphere

The cerebral hemispheres are separated by:

  • Seep midsagittal cleft called the longitudinal fissure of cerebrum (fissura longitudinalis cerebri).  It is occupied by the falx cerebri.
  • A short horizontal cleft named the transverse cerebral fissure (fissura transversa cerebri). The transverse cerebral fissure is usually called the telendiencephalic fissure because it separates these two parts. It is located beneath the posterior extension of the corpus callosum /splenium/ and above the roof of the 3rd ventricle. Through it passes the posterior chorioid arteries and the great cerebral vein.

The cerebral hemisphere has 3 surfaces, 3 borders, and 3 poles.

The superolateral surface of hemispheres, which is the convex surface and has four interlobular sulci (sulci interlobares) and points of divisions:

  • The central sulcus (sulcus centralis) – between the frontal and parietal lobe
  • The lateral sulcus (sulcus lateralis) includes:
  • Posterior ramus (ramus posterior) – between the frontal and temporal lobes
  • Anterior ramus (ramus anterior) on the frontal lobe
  • Ascending ramus (ramus ascendens) on the frontal lobe
  • Parieto-occipital sulcus (sulcus parietooccipitalis) between the parietal and occipital lobes
  • Preoccipital notch (incisura preoccipitalis)
  • The occipital transverse line – arbitrary line between parietal and occipital lobes joining preoccipital notch and parietooccipital sulcus

Medial surface is flat.

Inferior surface is basal surface consisting of two parts:

  • Orbital
  • Tentorial

On the medial and inferior surfaces of the hemisphere there are following interlobular sulci:

  • Sulcus of corpus callosum (sulcus corporis callosi)
  • Cingulate sulcus (sulcus cinguli)
  • Marginal branch or marginal sulcus (ramus marginalis seu sulcus marginalis)
  • Parieto-occipital sulcus (sulcus parietooccipitalis)
  • Collateral sulcus (sulcus collateralis)
  • Central sulcus (sulcus centralis)
  • Superior margin – between the superolateral and medial surfaces
  • Inferolateral margin – between the superolateral and basal surfaces
  • Inferomedial margin – between medial and basal surfaces has two parts:
    • Medial occipital – between tentorial and medial surfaces
    • Medial orbital – between orbital part and medial surfaces
  • Frontal pole (polus frontalis)
  • Occipital pole (polus occipitalis)
  • Temporal pole (polus temporalis)

All interlobular divisions (sulci & lines) separate five cerebral lobes:

  • Frontal lobe (lobus frontalis)
  • Parietal lobe (lobus parietalis)
  • Occipital lobe (lobus occipitalis)
  • Temporal lobe (lobus temporalis)
  • The insula (lobus insularis)
Location of central sulcus, and the major divisions of the cerebral lobes.
Lobes & poles of the cerebral hemispheres.

Frontal lobe (lobus frontalis) is the largest of all the lobes. It consists of:

  • Precentral sulcus (sulcus precentralis)
  • Superior frontal sulcus (sulcus frontalis superior)
  • Inferior frontal sulcus (sulcus frontalis inferior)
  • Precentral gyrus (gyrus precentralis)
  • Superior frontal gyrus (gyrus frontalis superior)
  • Middle frontal gyrus (gyrus frontalis medius)
  • Inferior frontal gyrus (gyrus frontalis inferior) is divided by the ascending and anterior rami of the lateral sulcus. The areas grouped around these two rami constitute the speech area of Broca. The speech area of Broca consists of:
    • Orbital part (pars orbitalis)
    • Triangular part (pars triangularis)
    • Opercular part (pars opercularis)
  • Medial frontal gyrus (gyrus frontalis medialis)
  • Paracentral sulcus (sulcus paracentralis)
  • Paracentral lobule (lobulus paracentralis) includes:
    • Anterior paracentral gyrus (gyrus paracentralis anterior)
  • Central sulcus (sulcus centralis)
  • Subcallosal area or gyrus (area subcallosa ) includes:
    • Paraterminal gyrus (gyrus paraterminalis)
  • Paraolfactory area (area paraolfactoria) includes:
    • Paraolfactory gyri (gyri paraolfactorii)
    • Paraolfactory sulci (sulci paraolfactorii)
  • Orbital gyri (gyri orbitales)
  • Orbital sulci (sulci orbitales) – H-shaped
  • Straight gyrus (gyrus rectus)
  • Olfactory sulcus (sulcus olfactorius)
  • Lateral olfactory gyrus (gyrus olfactorius lateralis)
  • Medial olfactory gyrus (gyrus olfactorius medialis)

Clinical comments

  • Sensory (receptive) Aphasia
  • Lexical Aphasia – inability to understand the meaning of words.
  • Syntactical Aphasia – inability to understand the relationship between words.

Diagram of the frontal lobe.
Gyri of frontal & temporal lobes of hemispheres.

Parietal lobe (lobus parietalis) consists of:

  • Postcentral sulcus (sulcus postcentralis)
  • Intraparietal sulcus (sulcus intraparietalis)
  • Marginal part of the parietooccipital sulcus
  • The distal part of the lateral sulcus
  • The distal part of the superior temporal sulcus
  • Superior parietal lobule (lobulus parietalis superior)
  • Inferior parietal lobule (lobulus parietalis inferior)
  • Supramarginal gyrus (gyrus supramarginalis)
  • Angular gyrus (gyrus angularis)
  • The parietooccipital sulcus (sulcus parietooccipitalis)
  • Subparietal sulcus (sulcus subparietalis)The distal part of
  • Cingulate sulcus
  • Precuneus (precuneus)
  • Postcentral part of the paracentral lobule includes:
  • Posterior paracentral gyrus (gyrus paracentralis posterior

Occipital lobe (lobus occipitalis) consists of:

  • Transverse occipital sulcus (sulcus occipitalis transversus)
  • Lunate sulcus (sulcus lunatus) and behind it:
    • Gyrus descendens (gyrus descendens)
  • Lateral occipital sulcus (sulcus occipitalis lateralis)short and horizontal divides the superolateral surface into:
    • Superior occipital gyrus (gyrus occipitalis superior)
    • Inferior occipital gyrus (gyrus occipitalis inferior)

Cuneus (cuneus)

  • Calcarine sulcus (sulcus calcarinus) – Y-shaped
  • Occipitotemporal sulcus (sulcus occipitotemporalis)
  • Parietooccipital sulcus (sulcus parietooccipitalis) separate
  • The distal part of the lingual gyrus (gyrus lingualis)
  • The distal part of the lateral occipitotemporal gyrus (gyrus occipitotemporalis lateralis)
  • The distal part of the medial occipitotemporal gyrus (gyrus occipitotemporalis medialis)
Gyri & Sulci of superolateral surface of the cerebral hemispheres.

Temporal lobe (lobus temporalis) consists of:

  • Superior temporal sulcus (sulcus temporalis superior)
  • Inferior temporal sulcus (sulcus temporalis inferior); both separate:
  • Superior temporal gyrus (gyrus temporalis superior)
  • Middle temporal gyrus (gyrus temporalis medius)
  • Inferior temporal gyrus (gyrus temporalis inferior)
  • Transverse temporal sulcus (sulcus temporalis transversus); both separate:
  • Anterior transverse temporal gyrus (gyrus temporalis transversus anterior)
  • Posterior transverse temporal gyrus (gyrus temporalis transversus posterior)
  • Occipitotemporal sulcus (sulcus occipitotemporalis)
  • Collateral sulcus (sulcus collateralis); both above separate
  • Lingual gyrus (gyrus lingualis)
  • Medial occipitotemporal gyrus (gyrus occipitotemporalis medialis)
  • Lateral occipitotemporal gyrus (gyrus occipitotemporalis lateralis)

Gyri & sulci of medial surface of the cerebral hemispheres.

The insula (lobus insularis)is a pyramidal-shaped area of the palium.  It is hidden accessory lobe of the hemisphere which is located deep in the lateral sulcus.  Coverings of the insula are called opercula.

The insula has three opercula:

  • Frontal operculum (operculum frontale) 
  • Parietal operculum (operculum parietale)
  • Temporal operculum (operculum temporale)

The insula is surrounded by the circular sulcus (sulcus circularis insulae) and the medial top of insula is called limen insulae – gyrus ambiens (limen insulae) . The cortex of insula is separated by the central sulcus (sulcus centralis) into:

  • The anterior part with three or four:
    • short gyri of insula (gyri breves insulae)
  • The posterior part, includes:
    • long gyrus of insula (gyrus longus insulae)
Gyri & sulci of insula

Gyri & sulci of inferior surface of the cerebral hemispheres.

Organization of the cerebral cortex

  1. Molecular layer or plexiform layer (lamina molecularis)
  2. External granular layer (lamina granularis externa)
  3. External pyramidal layer (lamina pyramidalis externa)
  4. Internal granular layer (lamina granularis interna)
  5. Internal pyramidal layer (lamina pyramidalis interna)
  6. Multiform layer (lamina multiformis)
  7. Stria of molecular layer or stria of plexiform layer (stria laminae molecularis)
  8. Stria of external granular layer (stria laminae granularis externae)
  9. Occipital stripe or occipital line (stria occipitalis)
  10. Stria of internal granular layer (stria laminae granularis internae)
  11. Stria of internal pyramidal layer (stria laminae pyramidalis internae)
  12. Tangential fibres (neurofibrae tangentiales)

Cerebral dominance and lateralization

Each cerebral hemispheres deals with the contra lateral side of the body.

Functions are performed using either hemisphere, but individuals “prefers” to use one hemisphere and this hemisphere thus performs better. When some higher functions are specific to one or to the other hemisphere it is cerebral dominance (“handedness”).

Predominantly, it is the left hemisphere which is dominant (98% of individuals), examples of which are:

  • Writing, throwing a ball, verbal, calculating and analytical thinking, motor function of the right part of the body.

If functions are performed using one hemisphere only it is a cerebral lateralization, examples of which are:

  • Language (usually left hemisphere)
  • Attention (usually right hemisphere)
  • Praxis (usually left hemisphere)
  • Spatial skills (usually right hemisphere)
  • Music and prosody (usually right hemisphere)
  • Computational skills (usually left hemisphere)

Precentral gyrus – primary motor area

Pars opercularis & pars triangularis of inferior frontal gyrus – MOTOR SPEECH AREA called as Broca’s area (dominant hemisphere). It coordinates muscles used in speech.

Functions of frontal lobe:

  • Motor functions, speech, cognition, higher levels affecting behaviour
  • Motor parts of the body are mapped to corresponding areas on the surface of the frontal cerebral cortex (precentral gyrus) and producing the MOTOR HOMUNCULUS. Lesions of specific areas of precentral gyrus produce loss of specific muscle functions (motor problems) on the opposite side of the body. It gives contra lateral spastic Upper Motor Neuron (UMN) paralysis.
MOTOR HUMUNCULUS – precentral gyrus.

Postcentral gyrus – primary sensory area. It receives general sensations from the opposite side of the body.

  • Posterior to postcentral gyrus – sensory association areas.
  • Supramarginal gyrus – higher perceptual mechanism for touch. It’s lesions gives tactile agnosia.
  • Angular gyrus of inferior parietal lobule – comprehension of written and visual objects.
  • Supramarginal gyrus & angular gyrus – SENSORY SPEECH AREA called as Wernicke’s area.

Functions of parietal lobe – Somatosensory processing

Sensory parts of the body are mapped to corresponding areas on the surface of the cerebral cortex and producing the SENSORY HOMUNCULUS. Damage of specific areas on the postcentral gyrus produce sensation problems on the opposite side of the body.

  • Calcarine sulcus – primary visual area
  • Primary visual area is surrounded by concentric bands and forms visual association areas
  • Functions of occipital lobe – Visual
  • Lesion of the occipital lobe:
  • Of the visual areas produces visual disorganization in contra lateral visual fields & defective spatial orientation.
  • Between the angular gyrus & occipital cortex produces defective interpretation of written language (alexia or visual agnosia).
  • Transverse gyrus of Heschl – primary auditory area, lies at the posterior end of superior temporal gyrus, on the temporal surface of lateral sulcus.
  • Sensory speech area or Wernicke’s area (supramarginal gyrus & angular gyrus). It’s lesions gives sensory aphasia (auditory association area).

Functions of temporal lobe – memory & audition

Functions of insular lobe Taste

Functions of limbic lobe – Primitive emotions, behaviour activity & olfaction

Results produced by injury to brain areas specialized for their functions:

  • Aphasia or dysphasia – language disorder of auditory or oral speech
  • Agraphia – disorder of writing
  • Alexia – disorder of reading
Cortical areas.

BROCA’S APHASIA – lesion causes disrupted speech.

  • Typically observed in patients with damage to left inferior prefrontal cortex.
  • Damage to “motor images”
  • Language comprehension skills are relatively preserved but functional words (i.e., adjectives, articles) are impaired.
  • That person has halting, agrammatic speech.

WERNICKE’S APHASIA – typically observed in patients with damage to left temporal cortex. A patient whose speech is fluent, but has no informational value.

  • Preserved function words, impaired content words.
  • Comprehension impaired.
  • Even simple sentences not well understood.
  • Associated with left temporal lobe damage.
  • Full of neologisms.
  • “Fluent nonsense”.
  • Broca’s & Wernicke’s areas are connected by arcuate fasciculus. Lesion of arcuate fasciculus gives conduction aphasia.

Amnesic aphasia is concerned with word-finding difficulties and implies that words have been “forgotten”,

Conduction aphasia is fluent aphasia with severely impaired repetition but relatively preserved language comprehension. Speech output is characterized by prominent phonemic (literal) paraphasias and word-finding difficulties. Patients with conduction aphasia have difficulty reading aloud because they make paraphasic errors, but they may have relatively good comprehension.

Global aphasia involves nearly all loss of all core linguistic functions including fluency, comprehension, repetition, reading, and writing. Large lesions involving both Broca’s area and Wernicke’s area (and nearby tissue) are generally involved.

Nonfluent aphasia is characterized by effortful speech production and lacks normal prosody. Nonfluent aphasia includes Broca’s aphasia, global aphasia, transcortical motor aphasia, and mixed transcortical aphasia. The term is used in contrast with fluent aphasia.

Receptive aphasia is characterized by relatively impaired comprehension as the prominent feature. It is associated with lesions in and around Wernicke’s area. This contrasts with expressive aphasia and is little used, as some comprehension difficulties occur with most aphasias.

Transcortical motor aphasia is nonfluent aphasia characterized by preserved repetition and relatively preserved language comprehension. This subtype is similar to Broca’s aphasia except for the preserved repetition. Lesions are typically vascular and involve the area superior or anterior to Broca’s area or the supplementary motor area.

Transcortical sensory aphasia is fluent aphasia in which language comprehension is severely impaired, but repetition is relatively preserved. Speech is circumlocutory, often with semantic jargon. This aphasia is similar to Wernicke’s aphasia except that repetition is preserved. Transcortical sensory aphasia has been described in the later stages of Alzheimer’s disease.

The cortical functional areas and their disabilities.

The white matter of hemisphere

  • The commissural fibres of neocortex Originate from pyramidal neuron cell bodies in lamina 3. They connect to the contra lateral cortical neurons, the cortical axons cross the midline. Commissural fibres of telencephalon:
  • Corpus callosum fibres –  interconnects most of cerebral cortex (except portions of the temporal lobes)
  • Anterior commissure or rostral commissure – interconnects portions of the temporal lobes
  • Fornix
  • Hippocampal commissure
Fibres of cerebral white matter: Corpus callossum – A; Anterior commissure – B; Forceps minor –C; Forceps major – D.

The association fibers originate from pyramidal neuron cell bodies in lamina 3. They include:

  • Arcuate fibres
  • Cingulum – interconnecting the cingulate gyrus with parahippocampal gyrus
  • Inferior longitudinal fasciculus
  • Superior longitudinal fasciculus or arcuate fasciculus – interconnecting Wernicke’s area and Broca’s area
  • Long association fibres and short association fibres
  • Uncinate fasciculus – interconnecting limbic areas (e.g., septal and periamygdaloid cortices)
  • Superior occipitofrontal fasciculus & inferior occipitofrontal fasciculus or subcallosal fasciculus – interconnecting visual areas with association cortices of frontal cortex
  • Vertical occipital fasciculus
  • Lateral fibres
  • Caudal fibres
  • Transverse occipital fasciculi
  • Cuneus fibres
  • Lingual fibres
Fibers of Cerebral White Matter (coronal section): Corpus callosum – A; Cingulum – B; Superior occipitofrontal fasciculus – C; Superior longitudinal fasciculus – D; Uncinate fasciculus – E; Inferior occipitofrontal fasciculus – F; Inferior longitudinal fasciculus – G; Internal capsule – H.
  • Thalamus (afferents make synaptic contact in lamina 4).
  • Other cortical areas have afferents that make synaptic contact principally in lamina 2 but also in other laminae.
  • Neuromodulatory from the midbrain (i.e., dopaminergic, noradrenergic, serotonergic).
  • Projection axons (i.e., those leaving cerebrum; efferents originate from pyramidal neurons in lamina 5).
  • Association axons (i.e., those making intra-cortical connections within the same hemisphere; efferents originate from pyramidal neurons in lamina 2).
  • Commissural axons (i.e., those making intra-cortical connections between homologous regions of the two cerebral hemispheres; efferents originate from pyramidal neurons in lamina 3).
  • Corticothalamic axons (i.e., projecting to thalamus from lamina 6).
Asspciation fibres of cerebral white matter: Lateral view (1): Superior longitudinal fasciculus – A; Inferior occipitotemporal fasciculus – B; Uncinate fasciculus – C; Perpendicular occipital fasciculus – D; medial view (2): Cingulum – A; Superior occipitofrontal fasciculus – B; Perpendicular occipital fasciculus – C; Inferior longitudinal fasciculus – D; Uncinate fasciculus – E

The projection fibres originate from pyramidal neuron cell bodies in lamina 5.

The commisures of telencephalon are formed by the:

Anterior commisure (commisura anterior) is a transverse connection between both hemispheres. It is visible in the anterior wall of the 3rd ventricle.

Corpus callosum (corpus callosum) called “the great commissure” consists of two parts:

Central part located on the floor of longitudinal brain fissure:

  • rostrum (rostrum) – the upper distal end
  • genu (genu) – the anterior bend of corpus callosum
  • trunk (corpus) – covered by the indusium griseum
  • splenium (splenium) – posterior thicker end

Peripheral part with four types of fibres:

  • Frontal
  • Parietal
  • Temporal
  • Occipital
Figure illustrating the projections of the fibres of the central
nervous system.

On the transverse section of the forebrain the fibres pass as:

Forceps minor (forceps frontalis seu minor) – U-shaped frontal fibres passing through genu of the corpus callosum and connecting the left and right frontal lobes.

Forceps major (forceps occipitalis seu major) – U-shaped occipital fibres passing through splenium of the corpus callosum and connecting the left and right occipital lobes.

The fornix (fornix) is an arcuate fold of the white matter with commisural fibres extends from the pes hippocampi to the mamillary body.

The fornix consists of five parts:

Fimbria (fimbria hippocampi) in the inferior horn of the lateral ventricle are the origin of crus.

Crus (crus) or posterior limb of the fornix arises from the inferior horn as hippocampal fibria and joins to the body of fornix at the central part of the lateral ventricule.

Commisure of fornix (commisura fornicis)  (lyra or psalterium) triangular connecting plate between crura of fornix,  below the posterior part of the corpus callosum. In the middle ages anatomists believed that it is location of the soul. 

Body of fornix (corpus fornicis) located on the floor of the central part of the lateral ventricle, is an unpaired middle part of the fornix which unites both crura. 

Column of fornix (columna fornicis) is anterior part of the fornix located in the 3rd ventricle. It extends to the mamillary body.

Ventricular system of the brain & subarachnoid spaces – Lateral ventricles

The lateral ventricles are irregular cavities in the cerebral hemisphere. Two lateral ventricles are almost completely separated from each other by the septum pellucidum (septum pellucidum). It is consists of two layers called lamina of septum pellucidum (lamina septi pellucidi) is separated by the cavity of septum pellucidum (cavum septi pellucidi). The lateral ventricle consists of central part and three horns.

Lateral ventricle – lateral view. Frontal horn – 1, central part – 2, occipital horn – 3, temporal – horn – 4.

The central part or body (pars centralis) is located in the parietal lobe. The central part is the middle portion of the lateral ventricles located above the thalamus and beneath the corpus callosum. It extends from the interventricular foramen (foramen interventriculare) to the splenium of the corpus callosum.

The central part has:

The roof or superior wall is formed by the inferior surface of the corpus callosum.

The floor or inferior wall is formed by:

  • Body of the caudate nucleus
  • Stria terminalis (stria terminalis) which is longitudinal stripe of white fibres,  above the superior thalamostriate vein,  located in the angle between body of caudate nucleus and thalamus.
  • Choroid plexus of lateral ventricle (plexus choroideus) which is vascularized complex (the choroid artery and vein) of vessels attached to:
    • Tenia choroidea (taenia choroidea) which is visible after removing the choroid plexus
    • Lamina affixa  

Lateral wall – body of caudate nucleus.

Medial wall – body of fornix, interventricular foramen.

Central part of lateral ventricle.
Lateral ventricle – superior view.

The frontal horn or anterior horn (cornu frontale seu anterius) is located in the frontal lobe. The anterior horn is continuous behind the interventricular foramen (of Monro).

It consists of three walls:

  • The roof is formed by the inferior surface of the corpus callosum.
  • Medial wall is built by the septum pellucidum.
  • Lateral wall is modelled by the head of the caudate nucleus.
Anterior horn of lateral ventricle.

The posterior horn consists of three walls: 

  • The roof is formed by fibres of the tapetum and radiation of corpus callosum
  • The floor – collateral triangle, collateral eminence
  • The lateral wall is formed by fibres of the tapetum
  • Medial wall is carved by:
    • Calcar avis or calcarine spur (calcar avis) internal expansion of the calcarine sulcus
    • Bulb of the occipital or posterior horn (bulbus cornus posterioris) is an enlargement caused by fibres of the splenium corporis callosi.
Posterior horn of lateral ventricle.

The temporal or inferior horn (cornu temporale seu inferius) is located in the temporal lobe. It consists of two walls:

Inferomedial wall is formed by:

  • Collateral eminence (eminentia collateralis) is an internal promontory caused by the collateral sulcus
  • Pes of hippocampus (pes hippocampi) is paw-like extremity of the hippocampus 
  • Fimbria of the hippocampus is a bundle of white fibres emanating from alveolus and continuos as crus of the fornix
  • Choroid plexus of lateral ventricle extends from interventricular foramen through the central part  to the inferior horn Choroid enlargement
  • Alveus of hippocampus

Superolateral wall is formed by:

  • Tapetum: temporal fibres of the corpus callosum
  • Tail of the caudate nucleus
  • Stria terminalis
  • Radiation of corpus callosum
  • Amygdaloid body

Inferior horn of lateral ventricle.

  1. What anatomical features of the cells called neurons are unique to that type of cell? And what are a few features that neurons share with all cells?
  2. What are the four types of glial cells in the nervous system? Where are they found and, briefly, what do they do?
  3. Name the parts of the neuron
  4. Name the target structures in the periphery innervated by axons that enter the PNS.
  5. Name two ways the nervous system makes use of the sensory information relayed to the cord by dorsal roots.
  6. What is a dermatome? Know the specific nerve root/s that supply the key dermatomes.
  7. What are the meninges? What tissue are they made up of?
  8. Know the lower extent of each of the three meninges.
  9. Learn the names of the spaces related to the meninges. Where is CSF found?
  10. Know what is meant by the terms ‘meningitis’ and ‘meningioma’.

Diencephalon (interbrain)

The diencephalons (diencephalon) or interbrain consists of the following parts:

  1. Thalamencephalon (thalamencephalon) with:
  2. The thalamus (thalamus)
  3. The metathalamus (metathalamus)
  4. The epithalamus (epithalamus)
  5. Hypothalamus (hypothalamus)
  6. Subthalamus (subthalamus)
  7. Third ventricle (ventriculus tertius)


The thalamus is an egg-shaped mass of grey matter, arranged into nuclei, and divided by two bands of white matter:

Internal medullary lamina (lamina medullaris interna) is Y-shaped white matter, composed of  three parts:

  • Posterior part which separates the medial and lateral nuclei.
  • Middle part (inferior bifurcation) which is situated around  the centromedian nucleus.
  • Anterior part (anterior bifurcation) which is situated around  the anterior nuclei.

External medullary lamina (lamina medullaris externa) separates the reticular nucleus and lateral cell mass from the thalami.

Each thalamus is situated on either side of the superior part of the third ventricle and medially to the posterior limb of the internal capsule. The thalamus has anterior (rostral) and posterior (caudal) poles.

Location of thalamus.

The thalamus has four surfaces:

The superior surface (facies superior) which is directed towards the central part of the lateral ventricle and it forms its floor.

There are six visible structures on the superior aspect of thalamus:

choroid plexus (plexus choroideus) of lateral ventricle, situated most medially on the superior surface of thalamus stria terminalis  (stria terminalis) a band of white matter, anastomising amygdaloid body ( corpus amygdaloideum ) and hypothalamus.

The terminal stria is situated most laterally between the caudate nucleus (nucleus caudatus) and the thalamus.

Thalamostriate vein (vena thalamostriata), an important tributary of  internal cerebral vein (vena cerebri interna) goes inside the stria terminalis.

Lamina affixa (lamina affixa) – a small plate of white matter, between terminal stria  and choroid plexus.

Anterior tubercule (tuberculum anterius).

Pulvinar (pulvinar) – a pillow-shaped part of superior aspect of the thalamus.

Choroid plexus (plexus choroideus) of lateral ventricle, situated most medially on the superior surface of thalamus stria terminalis (stria terminalis) a band of white matter, anastomising amygdaloid body (corpus amygdaloideum) and hypothalamus.

The terminal stria is situated most laterally between the caudate nucleus (nucleus caudatus) and the thalamus.

Thalamostriate vein (vena thalamostriata), an important tributary of internal cerebral vein (vena cerebri interna) goes inside the stria terminalis.

Lamina affixa (lamina affixa) – a small plate of white matter, between terminal stria and choroid plexus.

Anterior tubercule (tuberculum anterius).

Pulvinar (pulvinar) – a pillow-shaped part of superior aspect of the thalamus.

The inferior surface (facies inferior) is joined to the hypothalamus.

The medial surface (facies medialis) extends between medullar stria of thalami (stria medullaris thalami) and hypothalamic sulcus (sulcus hypothalamicus.).It gives the lateral wall of the third ventricle. There is a nuclear mass or the massa intermedia which connects the two thalami as interthalamic adhesion (adhesio  interthalamica) across the lumen of third ventricle,

The lateral surface (facies lateralis) which is joined with the posterior limb of the internal capsule and covered by external medullar lamina.

Connections between the thalamus, globus pallidus & subthalamic nucleus.

The neurons of the thalamus are arranged into nuclei. There is an anatomical and functional classification of the thalamic nuclei.   The principle of anatomical classification is related to the anatomical location.

The internal medullary lamina separates thalamic nuclei into medial, lateral and dorsal groups.

Anatomical classification of thalamic nuclei:

  • anteroventral nucleus (nucleus anteroventralis) – AV
  • anterodorsal nucleus (nucleus anterodorsalis) – AD
  • anteromedial nucleus (nucleus anteromedialis) – AM
  • Medial dorsal nucleus (nucleus mediodorsalis)
  • Medial ventral nucleus (nucleus medioventralis)
  • Ventrobasal complex (nucleus ventrobasalis)
  • Ventral anterior nucleus (nucleus ventralis anterior) – VA
  • Ventral medial complex (nuclei ventrales mediales) – VM
  • Ventral lateral nuclei (nuclei ventrales laterales) – VL
  • Ventral intermedius nucleus (nucleus  ventralis intermedius) VI
  • Ventralbasal complex (nuclei  ventrobasales ) – VB are subdivided into the:
    • Ventral posterolateral nucleus (nucleus ventralis posterolateralis) – VPL
    • Ventral posteromedialis nucleus (nucleus ventralis posteromedialis) – VPM
    • Ventral posterior inferior nucleus (nucleus  ventralis posterior inferior

Ventral anterior nucleus – VA  – influences activity of motor cortex

  • afferent fibres – premotor cortex, substantia nigra, corpus striatum, reticular formation, hypothalamus, other thalamic nuclei.
  • efferent fibres – premotor cortex, substantia nigra, corpus striatum, reticular formation, hypothalamus, other thalamic nuclei.

Ventral lateral nuclei – VL – influences motor activity of motor cortex.

  • afferent fibres – premotor cortex, substantia nigra, corpus striatum, reticular formation, hypothalamus, other thalamic nuclei, cerebellum, red nucleus.
  • efferent fibres – premotor cortex, substantia nigra, corpus striatum, reticular formation, hypothalamus, other thalamic nuclei.

Ventral posterolateral nucleus – VPL – relays common sensations to consciousness.

  • afferent fibres –  medial & spinal lemnisci.
  • efferent fibres –  primary somatic sensory (areas 3, 1, 2) cortex.

Ventral posteromedialis nucleus – VPM – relays common sensations to consciousness.

  • afferent fibres –  trigeminal lemniscus, gustatory fibres.
  • efferent fibres – primary somatic sensory (areas 3, 1, 2) cortex.

Lateral dorsal nucleus LD & lateral posterior nucleus – LP.

  • afferent fibres – cerebral cortex & other thalamic nuclei.
  • efferent fibres – cerebral cortex & other thalamic nuclei.
  • Lateral dorsal nucleus (nucleus lateralis dorsalis) – LD
  • Lateral posterior nucleus (nucleus lateralis posterior) – LP
  • Nucleus limitans (nucleus limitans)
  • Posterior nucleus (nucleus posterior)
  • Suprageniculate nucleus (nucleus suprageniculatus)
Divisions of the nuclei of thalamus.
Transverse section of the thalamus.
  • Sensory nuclei
  • Motor nuclei
  • Limbic nuclei
  • Associational nuclei

  • Intralaminar nuclei
  • Reticular nucleus (connect with other thalamic nuclei)

Relays & processes sensory & motor  information going to cerebral cortex:

  • Almost all of sensory information (except smell) converges on the thalamus.
  • Allows different areas of cortex to communicate with one another (especially, with information going to association areas of cortex).
  • Sets the “idle” for cerebral cortex, insuring that all areas of cortex receive continuous input (i. e., 3 persecond input).
Connections of the thalamus.

The metathalamus formed posterior part of halamencephalon situated below the pulvinar.

It has the geniculate bodies:

Lateral geniculate body (corpus geniculatum laterale) which is the part of thalamencephalon related to the sensory nucleus of visual pathway (retino-geniculo-calcarine pathway).

Medial geniculate body (corpus geniculatum mediale) which is the part of thalamencephalon related to the sensory nucleus of hearing.

The epithalamus is on the most dorsal part of thalamencephalon. It consists of several anatomical structures:

Habenula (habenula) which is composed of white matter. The nerve fibres of it start in the habenular trigon and go to the pineal body.  The function of habenula is uncertain. It is presumed to mediate olfactory stimuli and feeding behaviour.

Habenular trigon (trigonum habenulae) is occupied by middle and lateral habenular nuclei connected with the stria medullaris of thalamus (it is a white matter starting from peripheral part of rhinencephalon).

Habenular commissure (commissura habenularum) connects the habenular nuclei of the two sides.

Epithalamic or posterior commissure (commissura epithalamica).

Pineal body (corpus pineale) is situated just above the superior colliculi of the mesencephalon. It manufactures the melatonin – a hormone controlling the circadian rhythms.

Clinical comments

Malfunction of the pineal body may lead to the premature, incomplete or delayed puberty. Enlargement (tumor) of pineal body may close the aqueduct of midbrain and lead to the internal hydrocephalus.

  • Medial Habenular Nucleus
  • Lateral Habenular Nucleus


The hypothalamusis the most ventral part of diencephalon, located beneath the hypothalamic sulcus. It comprises the floor of the third ventricle. The ventral aspect of hypothalamus is easily seen between the cerebral hemispheres.

The hypothalamus is the most ventral part of diencephalon, located beneath the hypothalamic sulcus. It comprises the floor of the third ventricle. The ventral aspect of hypothalamus is easily seen between the cerebral hemispheres.

There are several important structures which belong to the hypothalamus:

  • Preoptic area (area preoptica) situated at the junction of the hypothalamus and the telencephalon.
  • Optic tract (tractus opticus).
  • Infundibular stalk (infundibulum) which joins the pituitary gland with tuber cinereum.
  • Hypophysis or pituitary gland (hypophysis).
  • Tuber cinereum (tuber cinereum) is the plate of grey matter, situated between optic chiasm and mammillary bodies.
  • Mamillary bodies (corpora mamillaria) are oval shaped structures with the nuclei. They are connected with the thalamus by the mamilothalamic tract (tractus mamillothalamicus).

Clinical comments

  • Disturbance with the temperature balance: hyperthermia/hypothermia.
  • Lost of appetite or excessive appetite: anorexia/hyperphagia.
  • Malfunctioning of the kidney, abnormal volume of urine (too small or too large) oliguria/polyuria, precocious puberty/delayed puberty.
  • Disturbance with the growth: gigantism/dwarfism, lathergy/aggression.
  • Uncontrolled twisting movements of the body: hemiballismus.

The hypothalamus displays some well-delineated nuclei and others with obscure boundaries referred to as a: anterior, middle and posterior group. The anterior nuclear area lies in the anterior part of hypothalamus before the column of fornix.

The paraventricular nucleus (nucleus paraventricularis), forms a plate of neurones along the wall of the third ventricle. It releases antidiuretic hormone (ADH, vasopresin) and oxitocin. 

The supraoptic nucleus (nucleus supraopticus) drapes over the optic tract. It releases ADH and oxytocin.

The preoptic nucleus (nucleus preopticus) lies anteriorly to the supraoptic nucleus. It controls the heat loss and parasympathetic excitation.

The suprachiasmatic nucleus  (nucleus suprachiasmaticus) drapes the optic chiasm. It receives retinal afferentes.

The lateral hypothalamic nucleus (nucleus hypothalamicus lateralis) extends towards the posterior part of the hypothalaums.

The venteromedial nucleus (nucleus venteromedialis),  large nucleus at the midhypothalamic level.

The dorsomedial nucleus (nucleus dorsomedialis), large nucleus at the midhypothalamic level. Both medial nuclei control appetite, fat metabolism and aggression.

The posterior hypothalamic nucleus (nucleus hypothalamicus posterior), lies in the posterior part of hypothalamus. It controls heat preservation, sympathetic excitation, mediates sleep-wake cycle and consciousness.

The middle mamillary nucleus (nucleus corporis mamillaris medialis).

The lateral mamillary nucleus ( nucleus corporis mamillaris lateralis).

The mamillary bodies are involved in short and long memory and circuit of Papaz.

The pituitary glandlies beneath the diaphragm of the sella in the hypophysial fossa on the sella turcica . It is divided into the parts with dual origin:

  • adenohypophisis (anterior part) – envagination from oral ectoderm.
  • neurohypophisis (posterior part) – envagination from the hypothalamus.

The pituitary gland communicates with the hypothalamus by the pituitary stalk (infundibulum). There are two neural tracts inside the pituitary stalk:

The tuberoifundibular tract (tractus tuberoinfundibularis), conveys axons and released hormones from the ventromedial, infundibular and tuberal nuclei of the hypothalamus to the portal blood system of the pituitary stalk.

The released hormones get to the adenohypophisis and control secretion of hypophysial trophic hormones.

The hormones of hypophisis control the function of organs and tissues (e.g. thyroid gland, suprarenal gland, ovary, testis, mammary gland, bone and fat tissue).

The hormones of adenohypophisis are the following:

  • TSH – thyroid stimulating hormone
  • ACTH – adrenocorticotropic hormone
  • LH – luteinizing hormone
  • FSH – follicle stimulating hormone
  • GH – growth hormone
  • PRL – prolactin
The location of the hypothalamus.

The supraopticohypophyseal tract (tractus supraopticohypophisialis) conveys the axons from supraoptic paraventricular nuclei to the neurohypohysis.

The axons of this tract release two hypothalamic hormones:

  • ADH (vasopresin) which controls the water absorption in  the kidney.
  • Oxitocin causes contraction of the uterus during delivery.

The subthalamus is situated between the thalamus and the hypothalamus near the internal capsule.

It is connected with the cerebral peduncle margins, and consists of the several structures:

Subthalamic nucleus (nucleus subthalamicus) controlling a autonomic activity.

Nuclei of perizonal fields – H, H1, H2 (nuclei campi perizonalis).

Zone incerta or uncertain zone  (zona incerta) is a plate of grey matter lying between thalamus, hypothalamus and subthalamic nucleus. It belongs to the extrapyramidal motor system.

Prerubral area  (area prerubralis) with the nuclei of field of Forel.

Ansa (loop) leticularis goes under the internal capsule, from the outer (lateral) portion of globus pallidus (GPi). Its fibers sweep ventromedially and rostrally around the posterior limb of the internal capsule & enters Forel’s field H.

Field H split into 2 laminae:

  • Field H1 is called thalamic fasciculus (fasciculus thalamicus) or Forel’s field H1.
    • Pallidothalamic tract
    • Dentatothalamic tract
    • Medial lemniscus
  • Field H2 is called lenticular fasciculus (fasciculus lenticularis). It goes from inner (medial) portion of GPi and perforate internal capsule enters Forel’s field H2.

Third ventricle

The third ventricle is empty space with cerebro-spinal fluid situated in the diencephalon. It is located between the thalami.

The third ventricle has six walls:

  • Superior wall composed of the tela choroidea, fornix and corpus callosum.
  • Inferior wall composed of the hypothalamus.
  • Lateral wall composed of medial walls of the thalami.
  • Anterior wall composed of the anterior commissure, lamina terminalis and columns of fornix.
  • Posterior wall composed of the habenular commissure and epithalamic commissure.

There are five recesses in the lumen of third ventricle:

  • Suprapineal recess (recessus suprapinelalis) above the habenular commissure.
  • Pineal recess (recessus pinealis) above the posterior commissure and below the habenular commissure.
  • Triangular recess (recessus triangularis) between the anterior commissure and columns of the fornix.
  • Optic recess (recessus opticus) between the border of floor and anterior boundary.
  • Infundibular recess (recessus infundibularis) above the infundibulum.
Ventricular system of the brain.
Outline of all relevant features of the third ventricle.


The brainstem is the common name for the following parts of the brain:

  1. Diencephalon
  2. Mesencephalon (midbrain)
  3. Pons
  4. Myelencephalon (Medulla oblongata)
  5. Bulb

Mesencephalon (midbrain)

The midbrain or mesencephalon controls motor and sensory functions including eye (head) movements, and the coordination of visual and auditory reflexes.

The midbrain consists of the:

  • Tectum
  • Mesencephalic aqueduct
  • Cerebral peduncles
    • Cerebral crura
    • Tegmentum
Divisions of the midbrain.
Midbrain – ventral view.
Transverse section of the midbrain.

The tectal plate has following parts:

Tectal plate with the superior colliculus and inferior colliculus (colliculus superior et colliculus inferior). Both colliculi are located below the splenium of the corpus callosum and they are separated by the transverse cerebral fissure.

They are composed of the nuclei:

  • Inferior colliculi nucleus receives auditory fibres and sends them to the medial geniculate body 
  • Superior colliculi nuclei receive fibres from the optic tracts, visual cortex medial lemniscus and send them to spinal cord, reticular formation and motor cranial nerve nuclei. These fibres form tectospinal tract, tectonuclear tract and tectoreticular tract.
  • Brachium of the superior colliculus connects the superior colliculi with the lateral geniculate body.
  • Brachium of the inferior colliculus joins the inferior colliculi with the medial geniculate body.

Triangles of lateral lemniscus  are located on  both sides laterally from inferior colliculus.

There are frenulum of superior medullary velum and trochlear nerve (CN IV) below tectal plate.

Mesencephalic aqueduct (aqueductus mesencephali seu aqueductus of midbrain) separates tectum, and the cerebral peduncles. It is a narrow canal extending between the third and fourth ventricle.

The cerebral peduncles protrude from the hemispheres and attach to the pons. The angle between them is about 80 degrees. The area circumscribed by the cerebral peduncles is called the interpeduncular fossa (fossa interpeduncularis). The bottom of this fossa is perforated by small blood vessels and is called posterior perforated substance (substantia perforata posterior seu interpeduncularis). The CN III emerges from this fossa.

The cerebral peduncles are divided by the substantia nigra (substantia nigra) into:

The basis or cerebral crus (crus cerebri) is the continuation downwards of the internal capsules pathways which pass to pons:

  • pyramidal tract (corticospinal and corticonuclear fibres).
  • corticopontine tract (frontopontine, occipitopontine, parietopontine and temporopontine fibres).
  • corticoreticular fibres.
The tracts of the cerebral crus.

The tegmentum (tegmentum mesencephali) means covering, the covering of the basis – is the plate of neurones and tracts sandwiched between the tectum and basis. The tegmentum is composed of white matter and grey matter.

Tegmental grey matter (nuclei) consists of:

Substantia nigra (substantia nigra). There are two parts of the substantia nigra: compact, and reticular.

Divisions of the substantia nigra.

It connects through afferent fibres with corpus striatum, cortex, subthalamic nucleus, raphe nuclei and superior colliculus; efferent fibres pass to striatum (fibres contain dopamine); besides substantia nigra connects with thalamus.

Tracts of the substantia nigra.

Reticular formation (formatio reticularis):

Red nucleus (nucleus ruber) consist of magnocellular and parvocellular parts. Afferent fibres pass to this nucleus through superior cerebellar peduncle from cerebellum; also afferent fibres pass to red nucleus from cortex, substantia nigra, reticular formation and superior colliculus. Efferent fibres form rubrospinal tract (to spinal cord), rubro-olivary tract and rubroreticular tract (to pons, midbrain and medulla oblongata).

  • Main afferent fibres: deep cerebellar nuclei and cortical motor areas (somatotopic organisaiton).
  • Main efferent fibres: crossed projections to deep cerebellar nclei, principal sensory trigeminal ncleus, facial.
Divisions and tracts of the red nucleus.

Rubrospinal tract facilitates muscle tone of distal flexors (ipsilateral, because 2x crossed).

Central grey substance (substantia grisea centralis) is located around the cerebral aqueduct; there are present dorsal raphe nucleus and nucleus of posterior commisure; there is tract called dorsal longitudinal fasciculus which passes from hypothalamus to metencephalon.

Interpeduncular nucleus (corpus interpeduncularis).

  • Sensory mesencephalic nucleus of the trigeminal nerve.
  • Motor nucleus of the trochlear nerve.
  • Motor and parasympathetic nuclei of the oculomotor nerve.

Tegmental white matter consists of long sensory tracts ascending from the spinal cord, cerebellum and pons. The most important are:

Medial lemniscus (lemniscus medialis) – originates from the nuclei gracilis and cuneatus (relay stations in the dorsal column pathway) and ends in a specific thalamic sensory nucleus.

Superior cerebellar peduncles (pedunculi cerebellares superiors) – originate in cerebellum and end in red nucleus; they cross midbrain and form decussation of superior cerebellar peduncles.

Lateral lemniscus (lemniscus lateralis) – the part of cochlear pathway originates from trapezoid body and ascends to the inferior colliculus and medial geniculate body.

Medial longitudinal fasciculus (fasciculus longitudinalis medialis) – anastomoses the motor nuclei of cranial nerves  for the muscle of eyeball (CN III, CN IV, CN VI) with stimuli from vestibular part of internal ear; it coordinates movements of head, neck and eyeball.

Dorsal longitudinal fasciculus (fasciculus longitudinalis lateralis)– anastomises the hypothalamus and parasympathetic nuclei of cranial nerves (CN III, CN VII, CN IX, CN X) and motor nuclei of  cranial nerves (CN VII, CN XII). Presumed function of dorsal longitudinal fasciculus is connected with the saliva secretion and tongue movements.

Vessels of the brain

The arterial brain system is supplied by two main trunks: the internal carotid arteries and vertebral arteries, wchich form the circle of Willis. Cerebral arteries have distinct territories of supply.

Distinguish between deep penetrating vessels of the brain stem (end arteries, no anastomoses in regions of end zones).

It arises from the first part of the subclavian artery.

Both vertebral arteries join together on the caudal border of the pons and form the basilar artery – BA (arteria basilaris).

It passes superiorly through the transversal foramen on each of the cervical vertebrae above C7. It pierces above the C1 atlanto-occipital membrane and runs into the posterior cranial fossa through the foramen magnum. VA is located on each side of the anterior surface of the medulla.

  • Posterior inferior cerebellar artery (arteria cerebellaris posterior inferior)
  • Posterior spinal artery (arteria spinalis posterior)
  • Anterior spinal artery (arteria spinalis anterior)

On the caudal border of the pons at the point where two vertebral arteries join together.

It terminates at the anterior border of the pons and at that point bifurcates into two posterior cerebral arteries.

It passes on the anterior surface of the pons in the midline.

  • Anterior inferior cerebellar artery  (arteria cerebellaris anterior inferior)
  • Superior cerebellar artery  (arteria cerebellaris superior )
  • Labyrinthine artery  (arteria labyrinthi)
  • Pontine arteries (arteriae pontis)
  • Posterior cerebral arteries (arteriae cerebralis posterior), wchich are formed by bifurcation of the BA. It turns laterally and posteriorly and passes above the crus cerebri. It runs backwards along the lateral aspect of the midbrain. The posterior cerebral artery supplies the inferior and medial surface of the temporal and occipital lobes. They give off two main branches:
    • posterior temporal artery (arteria temporalis posterior)
    • internal occipital artery (arteria occipitalis interna)

The cerebral arterial circle (circulus arteriosus cerebri) or the circle of Willis is formed by:

  • anterior communicating artery
  • middle cerebral arteries
  • posterior communicating arteries
  • posterior cerebral arteries
Arteries of the base of the brain. Structure of the circle of Willis.

The Internal Carotid Artery (ICA) (arteria carotis interna) – supplies the greater part of the brain and the contents of the orbit.

It arises from the bifurcation of the common carotid artery /CCA/ at the level of the upper border of the thyroid cartilage.

It terminates intracranially in the middle cranial fossa, medial to the anterior clinoid process of the sphenoid bone.

The ICA ascends to the base of the skull at first being located posterolaterally to the external carotid artery then medially to that artery.  ICA leaves the neck by passing through the carotid canal of the petrous part of the temporal bone. It passes upwards and forwards by the cavernous sinus,  pierces  the roof of the sinus, and turns backwards on itself before dividing into the anterior and middle cerebral arteries.

Branches of cranial part of the ICA: ICA does not provide any branches to the neck. Main branches of the internal carotids:

  • Anterior cerebral artery (recurrent artery of Heubner)
  • Middle cerebral artery  (lenticulostriate arteries, anterior choroidal artery)

Caroticotympanic branches (rami caroticotympanici), a small vessel in the carotid canal.

Pterygoid arteries (arteriae canalis pterygoidei ) in the pterygoid canal.

Meningeal branch (r. meningeus).

Posterior communicating artery, (arteria communicans posterior) anastomise with the middle and posterior cerebral arteries.

Anterior cerebral artery , (arteria cerebri anterior) arises at the bifurcation of the ICA passes dorsally to the optic nerve and communicate with one another via anterior communicating artery (arteria communicans anterior). Then it passes along the longitudinal fissure. It supplies the medial aspect of the hemispheres as far posteriorly as the parieto-occipital fissure.

Middle cerebral artery (arteria cerebri media) is a continuation of the ICA and runs to the lateral cerebral fossa. It terminates as the cortical branches. The large number of the branches supply the lateral aspect of the hemispheres.

Ophthalmic artery (arteria ophthalmica) and its branches.

1. Pericallosal artery 2. Callosomarginal artery 3. Anterior Cerebral Artery (ACA) 4. Middle Cerebral Artery (MCA) 5. Internal Carotid Artery (ICA) 6. Middle meningeal artery 7. Maxillary artery 8. Occipital artery

Clinical comments

Continuous blood supply is critical for normal functioning of CNS. Even short (a matter of seconds) anoxia and ischemia can produce neurological symptoms. If they last several minutes, symptoms can be irreversible. Pathological conditions include stroke or cerebrovascular accidents.

The veins of the CNS are divided into two groups (superficial and deep). All veins are devoid of valves as are the dural sinuses.

The superficial group of veins take origin from the surface of the cortex and subcortical white matter. It consists of:

  • Superior cerebral veins (venae cerebri superiores) drain the middle surface of the hemispheres and joins the superior sagittal sinus.
  • Inferior cerebral veins (venae cerebri inferiores)collect the blood from the inferior  surface of the hemispheres and join the basal sinus.
  • Superficial cerebral vein (vena cerebri superficialis) receives blood from the many veins from the surface of the hemispheres and joins the cavernous sinus.

Deep group of the veins consists of:

Internal cerebral vein (vena cerebri interna) receives blood from veins around the roof of the third ventricle:

  • choroid vein (vena choroidea)
  • thalamstriate vein (vena thalamostriata)
  • septal vein (vena septalis)
  • epithalamic vein (vena epithalamica)
  • lateral ventricular vein (vena ventriculi lateralis)

Basal vein (vena basilaris) lies under the medial  part of the anterior lobe.

It receives:

  • anterior cerebral vein (vena cerebri anterior)
  • deep middle cerebral vein (vena cerebri media profunda)
  • inferior striate vein (vena striata inferior)

Great cerebral vein (of Galen), (vena cerebri magna) empties into the rectal sinus.

It receives blood from:

  •  internal cerebral veins
  •  basal veins
  •  occipital veins
  •  posterior callosal vein


The metencephalon (metencephalon) consists of three parts: (1) the isthmus of the hindbrain, (2) pons, (3) cerebellum

The isthmus of hindbrain (isthmus of rhombocephalon) (isthmus rhombencephali) forms a dorsal border between the midbrain and the rhombencephalon. The trochlear nerve (CN IV) lies on this part. The isthmus has three elements:

  1. Superior medullary velum (velum medullare superius) thin sheet of white matter, pia and ependyma.
  2. Superior cerebellar peduncule (pedunculus cerebellaris superior) joins the cerebellum with the midbrain (red nucleus).
  3. Triangle of lateral lemniscus (trigonum lemnisci).

The pons (pons) and the middle cerebellar peduncule are devided by an arbitrary line at the level of trigeminal nerve. The trigeminal nerve marks the border between the pons and the middle cerebellar peduncule. There is bulbopontine sulcus which separates pons and medulla oblongata. 

Pons consists of:

Longitudinal triads – tectum of pontis consisting anterior /superior/ medullary velum, tegmentum, basis

Peduncular triads – three paired peduncules – superior, middle and inferior- attach the cerebellum to the pons      

Motor cranial nerve triads – CN V, CN VI, and CN VII

Sensory cranial nerve triads – cochlear and vestibular nuclei of CN VIII , sensory nucleus of CN V

Pons has two surfaces:

Anterior surface (base of the pons) (basis pontis) include:

Basilar sulcus (sulcus basilaris) for the basilar artery.

Longitudinal pontine fibres (fibrae pontis longitudinales) consist of:

  1. Corticospinal fibres (fibrae corticospinales) part of the piramidal tracts running into the spinal cord.
  2. Corticonuclear or corticobulbar fibres (fibrae corticonucleares) part of the pyramidal tracts running to the motor nuclei of the cranial nerves.
  3. Corticoreticular fibres (fibrae corticoreticulares) fibres passing from the palium to the reticular formation.
  4. Corticopontiane fibres (fibrae corticopontinae) fibres passing from the frontal occipital and temporal lobes to the pontine nuclei.

Transverse pontine fibres (fibrae pontis transverse) – fibres of the cerebropontocerebellar tracts.

Pontocerebellar fibres (fibrae pontocerebellaris) fibres which pass to middle cerebellar peduncles.

Pontine nuclei (nuclei pontis) like anterior nucleus, lateral nucleus, median nucleus, paramedian nucleus, posterior nucleus, posterolateral nucleus, posteromedial nucleus.

Posterior surface: superior part of the rhomboid fossa or tegmentum of pons includes:

Trapezoid body (corpus trapezoideum) forming a part of auditory pathway with anterior & posterior trapezoid body nuclei (nucleus corporis trapezoidei anterior et posterior):

  • Medial lemniscus (lemniscus medialis)   
  • Spinal lemniscus ( lemniscus spinalis )
  • Trigeminal lemniscus ( lemniscus trigeminalis )
  • Central grey substance ( substantia grisea centralis )
  • Lateral lemniscus ( lemniscus lateralis ) 
  • Nuclei of the cranial nerves CN V-VIII
  • Reticular formation (formatio reticularis) is combination of small nuclei which are concerned with the integration of visceral and muscular functions.

Pons intermediates with conducting impulses from cortex to cerebellum. There are present a lot of pathways from all parts of cortex  which end in nuclei of pons – corticopontine fibres. Then they pass to cerebellum through middle cerebellar peduncles. Besides pons connects with reticular formation.

The rhombencephalon.

The cerebellum (cerebellum) is located in posterior cranial fossa above the fourth ventricle. It has:

  • Two surfaces:
    • Superior surface
    • Inferior surface with vallecula of cerebellum
  • Two margins:
    • Anterior margin and anterior incisure.
    • Posterior margin and posterior incisure.
  • Two main parts:
    • Vermis (vermis ) – central part of the cerebellum, it includes:
      • superior vermis.
      • inferior vermis (on the floor of the vallecula cerebelli).
    • Hemisphere of cerebellum (hemispherium cerebelli) two of them which forme lateral part of cerebellum.

Surface of cerebellar cortex forms cerebellar fissures and folia of cerebellum.

Lobes of the cerebellum A) vermis of cerebellum, B) hemisphere of cerebellum,
1 – primary fissure, 2 – horizontal fissure, 3 – posterolateral fissure.

The cerebellum is a part of motor system. It is responsible for unconscious coordination and fine control  of muscle actions. It can’t initiate conscious movements by itself.

The cerebellum communicates with others structure through the:

  • Superior (rostral) cerebellar peduncle – mostly efferent from the deep cerebellar nuclei projecting to thalamus and red nucleus. These fibers cross in the decussation of the superior cerebellar peduncles. Afferents include the ventral spinocerebellar tract.
  • Middle (pontine) cerebellar peduncle – entirely afferent from pons (carrying pontocerebellar input).
  • Inferior (caudal) cerebellar peduncle – mostly afferents from the spinal cord (exception: vestibulocerebellar). Fibers are going to vestibular nuclei.

There are three following lobes of the cerebellum:

  1. Anterior lobe of cerebellum (lobus cerebelli anterior) extends from the superior medullary velum to the primary fissure
  2. Posterior lobe of cerebellum (lobus cerebelli posterior) lobe extends from the primary fissure to the posterolateral fissure
  3. Flocculonodular lobe (lobus flocculonodularis) = nodule + flocculus

Usually the cerebellum is divided into following lobules:

Subdivision of cerebellum (lobules, top to bottom)

VermisHemispheres of cerebellum
Superior surface
Central lobuleWing of central lobule
CulmenQuadrangular lobule
Primary fissure
DecliveSimple lobule
Folium of vermisSuperior semilunar lobule
Horizontal fissure
Inferior surface
tuber of vermisinferior semilunar lobule
pyramid of vermisbiventer lobule
uvula of vermistonsil of cerebellum
Posterolateral fissure
Subdivision of cerebellum (lobules, top to bottom).
  • Central lobule
    • Posterior part; Dorsal part
    • Anterior part; Ventral part
  • Wing of central lobule
    • Inferior part; Ventral part (H II)
    • Superior part; Dorsal part (H III)
  • Quadrangular lobule
  • Anterior quadrangular lobule
  • Superior semilunar lobule
  • Ansiform lobule
    • First crus
    • Second crus
  • Biventer lobule
  • Dorsal parafloccular lobule
  • Inferior semilunar lobule
  • Paramedian lobule
  • Gracile lobule
Structure of the central and lateral parts of the cerebellum Vermis of cerebellum: 1) lingula, 2) central lobule, 3) culmen, 4) declive, 5) folium of vermis, 6) pyramid of vermis, 7) tuber of vermis, 8) Uvula of vermis, 9) nodule

The internal structure of the cerebellum consists of the:

  • White matter = medullary cortex (arbor vitae)
  • Grey matter which consists of two parts:
    • Cerebellar cortex
      • Molecular layer
      • Ganglionar layer
      • Granular layer
    • Cerebellar nuclei
  • Dentate nucleus or nucleus lateralis cerebelli (nucleus dentatus) which is the largest and the most lateral of the cerebellar nuclei, with characteristic corrugated or tooth-like outline. It has hilum of dentate nucleus (hilum nuclei dentati).
  • Emboliform nucleus or anterior interpositus nucleus (nucleus emboliformis).
  • Globose nucleus or posterior interpositus nucleus (nucleus globosus).
  • Fastigial nucleus or nucleus medialis cerebelli (nucleus fastigii). Its name comes from its location near the fastigium of the fourth ventricle.
Nuclei of the cerebellum.

Archicerebellum or flocculonodular lobe – functionally vestibulocerebellum responsible for maintenance of equilibrium, posture and balance. The deficit syndromes are as follow: vertigo, nystagmus, truncal, stance and gait ataxia, vomiting.

Paleocerebllum is formed by the anterior lobe of cerebellum, partly vermis and medial part of posterior lobe, functionally spinocerebellum responsible for regulation of muscle tone. The deficit syndromes are as follow: ataxia of lower limb mainly, oculomotor dysfunction, speech disorder, asynergy of speech muscles.

Neocerebellum is formed by the lateral part of posterior lobe, functionally it is the pontocerebellum (cerebrocerebellum) responsible for skilled movements. The deficit syndromes are as follow: dysmetria, hypermetria, positive rebound, intention tremor, nystagmus, decreased muscle tone.

Main connections of the paleocerebellum.

Inferior Cerebellar Peduncle contains afferent and efferent fibers:

Restiform body

  1. Posterior or dorsal spinocerebellar tract (ipsilateral) between posterior thoracic nucleus to vermis close to the anterior lobe and pyramid close to posterior lobe of cerebellum. It relays proprioception and cutaneous sensation from lower limb.
  2. Cuneocerebellar tract (ipsilateral) between the nucleus cuneatus and posterior part of anterior lobe of cerebellum. It relays proprioception and cutaneous sensation from upper limb, functionally it corresponds to the posterior spinocerebellar tract.
  3. Olivocerebellar tract from inferior olivary nucleus. It receives sensory and motor inputs and large contralateral projections from cerebellum as well.
  4. Arcuatocerebellar tract
  5. Reticulocerebellar tract
  6. Trigeminocerebellar tract

Juxtarestiform body

  1. Vestibulocerebellar tract (direct & secondary)
  2. Primary vestibular fiber

Middle Cerebellar Peduncle contains only afferent fibers:

  1. Pontocerebellar tracts (fibers).
  2. Corticopontocerebellar fibers.
  3. Reticulocerebellar fibers.

Superior Cerebellar Peduncle containsmostly efferent fibers from cerebellar nuclei:

  1. Anterior spinocerebellar tract relays proprioception (muscle spindle, tendon receptors, etc.) fibers from dorsal root ganglion cells, lower limb and trunk. The fibers cross locally and then re-cross in the pons to return to the ipsilateral side. They terminates in vermis and intermediate part of anterior lobe of cerebellum.
  2. Cerulocerebellar fibers
  3. Raphecerebellar fibers
  4. Rubrocerebellar fibers
  5. Hypothalamocerebellar fibers
  6. Tectocerebellar tract

Superior cerebellar peduncle:

  1. Cerebellothalamic fiber: from dentate nucleus, emboliform nucleus and globose nucleus to VPLo, VLc, CL
  2. Cerebellorubral fibers: to red nucleus in mesencephalon from nucleus interpositus and dentate nucleus ascending portion of Uncinate fasciculus of Russell – dentatorubrothalamic tract (brachium conjunctivum)
  3. Superior cerebelloreticular tract: to reticular formation in mesencephalon, pons and medulla oblongata

Inferior cerebellar peduncle:

  1. Cerebellobulbar tracts: start in fastigial nucleus and archicerebellum. Fibres pass partly with vestibulocerebellar tract and partly as uncinate fasciculus. All fibres end in vestibular nuclei as cerebellovestibular tract and in nuclei of medulla oblongata reticular formation as inferior cebelloreticular tract.
  • Caudal portion of medial and dorsal accessory olivary nucleus:
    • Vermis of cerebellar cortex (A and B)
    • Fastigial nucleus
    • Vestibular nucleus
  • Rostral portion of medial and dorsal accessory olivary nucleus:
    • Paravermal region (C1, C2, C3)
    • Nucleus interpositus
  • Principal inferior olivary nucleus:
    • Cerebellar hemisphere (D1, D2)
    • Dentate nucleus

Function: A timing computer, where motor commands (intended movements) are compared with proprioceptive feedback information (actual movements), allowing the CNS to make appropriate adjustments to the motor commands.

Circuity of the cerebellum.

Spinocerebellum formed by vermis and adjacent territory of the hemispheres. It contains the interposed nuclei of the deep cerebellar nuclei. Spinocerebellum receives sensory feedback input from ipsilateral part of spinal cord through:

  1. Clarke’s nucleus for the lower limb (dorsal spinocerebellar tract).
  2. Accessory cuneate nucleus for the upper limb (cuneocerebellar tract).

It has reciprocal (mutual or joint) connections with:

  1. reticular formation to control axial musculature.
  2. contralateral primary motor cortex (areas controlling axial musculature) to control on-going motor activities.
Functional division of the cerebellum.

Pontocerebellum (cerebrocerebellum) formed by lateral regions of the cerebellar hemispheres. It contains dentate nucleus of the deep cerebellar nuclei.

Pontocerebellum receives sensory feedback input from contralateral motor cortex (via a relay in the basilar pontine nuclei).

It sends output to pre-motor cortex (via a relay in the VA/VL nuclei of thalamus) to control motor planning, initiation and timing of movements.

Vestibulocerebellum is formed by flocculus, and nodulus.

Vestibulocerebellum contains fastigial nucleus of the deep cerebellar nuclei.

It receives input from vestibular nuclei.

It sends output to vestibular nuclei to control balance.

Main connections of the vestibulocerebellum.
  1. Maintenance of equilibrium: characterized by unsteady walking and swaying when standing, balance, posture, eye movement.  All sings give the lesions of vestibulocerebellum (flocculus, nodulus and posterior part of vermis).
  2. Coordination of half-automatic movement of walking and posture maintenance – posture, gaits (asynergy – loss of coordination).
  3. Adjustment of muscle tone
  4. Motor leaning – motor skills
  5. Cognitive function

Unilateral lesions of the cerebellum lead to motor disabilities IPSILATERAL to the side of lesions. Ataxia is a loss of the coordinated muscular contractions required for the production of smooth movements called hypotonia. Alcohol intoxication can mimic cerebellar ataxia.

  • Ataxia: unncoordination of movements, truncal ataxia when patient can’t sit quietly upright is distinguished from stance or gait ataxia with impaired limb movements (unsteady gait in inebriation). Patient stands with leags spread apart and places his hand on wall for stability.
  • Asynergy: is lack of coordination between different muscle group.
  • Dysmetria: an inability to place an extremity at a precise point in space  (touch the finger to the nose), past-pointing.
  • Dysdiadochokinesia or adiadochokinesia: is an inability to make or  difficulty in making, successive or rapidly alternating movements (ataxia of gait) with the tendency to fall toward the side of the lesions.
  • Intention tremor: involuntary, it arises when voluntary movements are attempted (finger – nose test).
  • Hypotonia: diminished muscle tone.
  • Nystagmus: rhythmic oscillations of the eyeballs.
  • The cerebellar hemisphere syndrome: ataxia & hypotonia of the ipsilateral extremities.
  • The anterior vermis syndrome: ataxia of the legs & trunk during walking, partly or no involving of upper extremities or of the speech or eye muscles, especially in chronic alcoholic patient.
  • The flocculonodular lobe or posterior vermis syndrome: ataxia of the trunk, often nystagmus.
  • The pancerebellar syndrome: bilateral ataxia, dysarthria, nystagmus, hypotonia of all voluntary muscles.
  • Archicerebellar lesion: medulloblastoma.
  • Paleocerebellar lesion: gait disturbance.
  • Neocerebellar lesion: hypotonia, ataxia, tremor.

Medulla oblongata

The medulla oblongata (medulla oblongata), myelencephalon or bulb: on the anterior (ventral) surface extends from the lower border of the pons to the pyramidal decussation. On the posterior (dorsal) surface of it we can find only the beginning at the medullary striae.

Medulla oblongata has two surfaces:

Ventral (basilar) surface includes:

  1. Anterior median fissure (fissura mediana anterior) iscontinuous with the spinal cord. Anterior median fissures of the medulla oblongata and spinal cord are separated by:
  2. The pyramidal decussation (decussatio pyramidum) – the crossing of the majority of the corticospinal tracts.
  3. Pyramid (pyramis) which is the elevation of the pyramidal tract with laterally  located anterior lateral sulcus (sulcus anterolateralis)  for exit of CN XII.
  4. Olive (oliva) which is a bean-shaped prominence produced by the nuclei lying below . It is located between outlets of CN X and CN XII. Inferior part of olive is covered by external arcuate fibres.

Superomedial or inferior part of rhomboid fossa

Posterior median sulcus (sulcus medianus posterior) which is the posterior groove closed at the top by the obex.

Gracile fasciculus (fasciculus gracilis) which is the medial part of posterior funiculus coming from the lower part of the half of the body with termination called gracile tubercule (tuberculum gracilis) or clava which is the  swelling over the nucleus gracilis.

Cuneate fasciculus (fasciculus  cuneatus) which is the lateral part of posterior funiculus coming from the upper half part of the body, with termination called: cuneate tubercule (tuberculum cuneatus) which is the  swelling of the cuneate fasciculus over the nucleus cuneatus.

Posterior lateral sulcus (sulcus posterolateralis)  which is the groove with  outlets of CN IX , CN X and the cranial part of CN XI reaching up to the lateral recess of the 4th ventricle.

Tuber cinereum (tuberculum cinereum) with spinal nucleus of trigeminal nerve; it is located laterally to cuneate tubercule.

There are two parts on the horizontal cross-section:

Olivary or superior part includes:

  • Olivary nuclei – inferior olivary nucleus and accessory olivary nuclei
  • Vestibular nuclei
  • Cochlear nuclei
  • Accessory cuneate nuclei
  • Spinal lemniscus
  • Central grey substance
  • Reticular formation

Infraolivary part includes:

  • middle – sensory decussation – decussation of the lemnisci
  • inferior – motor decussation –  pyramidal decussation
  • ambiguous nucleus
  • cuneate nucleus
  • gracilis nucleus
  • nuclei of cranial nerves
  • central grey substance
  • reticular formation

Inferior olivary nucleus (nucleus olivaris inferior) which is the main olivary nucleus located beneath the olive includes:

  • Hilum of inferior olivary nucleus (hilum nuclei olivaris inferioris) is an opening of the sack-like olivary nucleus facing towards the medial direction.

Clinical comments

Inferior olivary nucleus is connected to the motor co-ordination through projections to the cerebellum. It is the single source of ascending fibres to the cerebellum. Axons arising from cells in the inferior olive cross enter the inferior cerebellar peduncle to reach the contralateral cerebellar cortex /nucleus which receives a variety of motor inputs that you do not need to know.

Lesions of the inferior olivary nucleus result in motor disco-ordination of the contralateral arm and leg. Cerebellar lesions result in motor disco-ordination of ipsilateral ones.



Nucleus ambiguus (nucleus ambiguus)  which is a motor nucleus of the CN X, CN IX and cranial portion of CN XI located after the olive.

Clinical comments

Nucleus ambiguus is connected with motor innervation of ipsilateral muscles of the soft palate, pharynx, larynx and upper esophagus. Axons of motor neurons in the nucleus ambiguus course with three cranial nerves: CN IX, CN X and cranial portion of  CN XI  to innervate striated muscles.

Lesion of nucleus ambiguus results in atrophy /lower motor neuron/ and paralysis of muscles, producing nasal speech, dysphagia, dysphonia, and deviation of the uvula towards the contralateral side. There is no problems  with the sternocleidomastoideus and trapezius because these muscles are innervated by cells in the lower portion CN XI located at the spinal cord.

Gracile nucleus (nucleus gracilis) and cuneate nucleus (nucleus cuneatus)  are connected with discriminative touch, conscious proprioception, and vibration sense from the leg, trunk, and arm. Central processes of dorsal root neurons T7 and below ascend ipsilateral fasciculus gracilis to reach nucleus gracilis in the caudal medulla oblongata. Processes of dorsal root ganglion cells T6 and above ascend in ipsilateral fasciculus cuneatus and end in nucleus cuneatus. Axons from cells in nucleus gracilis and cuneatus pass ventrally as internal arcuate fibres, cross the midline and form the medial lemniscus. Medial lemniscus ascends to ventral posterior lateral nucleus of the thalamus /VPL/. Cells in VPL project to somatosensory cortex.

Clinical comments

Lesions in the fasciculus gracilis, nucleus gracilis, fasciculus cuneatus and nucleus cuneatus result in ipsilateral deficits in 2 point discrimination, vibration sense, and conscious proprioception from the leg and arm respectively. Lesion in the medial lemniscus results in contralateral deficits. Lesions in the internal arcuate fibres before they cross the midline result in ipsilateral deficits. Lesion of crossing fibres from both sides may cause bilateral deficits.

Reticular formation (formatio reticularis ) is an ill-defined system of scattered neurones    intermingled with fibres running longitudinally. It is a net-like mixture of grey and white matter of the midbrain, pons, medulla oblongata and spinal cord).

  • Lateral lemniscus connects trapezoid body superior olive with inferior colliculus. Function: auditory pathway.
  • Medial lemniscus connects nucleus cuneatu and gracillis (nuclei of dorsal column) with thalamus. Function: touch, conscious proprioception of the trunk and limbs.
  • Spinal lemniscus connects lateral and anterior spinothalamic tract (posterior horns). Function: pain pathway for trunk and limbs.
  • Trigeminal lemniscus connects sensory trigeminal nuclei with thalamus. Function: sensory pathway for head.
Transverse section of medulla oblongata on the level of pyramid deccusation.

Fourth ventricle

The fourth ventricle is a tent-shaped space lying dorsal to the pons and cranial part of the medulla oblongata, and ventral to the cerebellum. The fourth ventricle consists of two parts:

The floor (rhomboid fossa) is diamond-shaped. It is divided into two parts by striae medullares of the fourth ventricle:

Rostal part includes:

  • The medial eminence (eminentia medialis) which is an elevation located between the sulcus limitans and median sulcus.
  • Facial colliculus (colliculus  facialis) which is an bulge produce by the internal genu of the CN VII and the nucleus of CN VI.
  • Upper part of the sulcus limiting (sulcus limitans) which is a shallow groove located laterally to the medial eminence.
  • Locus ceruleus (locus ceruleus) which is a shallow furrow extending inferiorly from the mesencephalic aquedact to:
    • The fovea superior (fovea superior) a pit located lateral to the facial colliculus

  • Hypoglossal triangle (trigonum nervi hypoglossi) which is located betwen the sulcus limitians and median sulcus.
  • Vagal triangle (trigonum nervi vagi) inferior to the hypoglossal triangle.
  • Funiculus separans (funiculus separans) which is situated between both above triangles.
  • The fovea inferior (fovea inferior) a pit located at the peak both above triangles.
The rhomboid fossa.

The median sulcus divides the rhomboid fossa into two trigones (the left trigone, and the right trigone) divided by the sulcus limitans into the lateral part, and medial part.

  • Lateral part includes:
    • The vestibular triangle (trigonum vestibularis) or vestibular area
  • Medial part includes:
    • Medial eminence but it is divided by the striae medullaris into:
      • Facial colliculus (above)
      • Hypoglossal triangle (below)

Floor of fourth ventricle or inferior wall structures:

  • median sulcus
  • medial eminence
  • facial colliculus
  • locus caeruleus
  • medullary stria of fourth ventricle
  • triangle of hypoglossal nerve
  • triangle of vagus nerve
  • vestibular area
  • funiculus separans
  • grey line or tenia cinerea

The roof has two parts, and a fastigium:

Superior part includes:

  1. The left superior cerebellar peduncule
  2. The right superior cerebellar peduncule
  3. Superior medullary velum (velum medullare superius)  (between left & right superior cerebellar peduncules).

Inferior part includes:

  1. Nodule
  2. flocculus
  3. Inferior medullary velum

Roof of fourth ventricle or superior wall structures

  • fastigium
  • tela choroidea of fourth ventricle
  • choroid plexus of fourth ventricle
  • lateral recess
    • lateral aperture
  • superior medullary velum
  • frenulum of superior medullary velum
  • inferior medullary velum
  • median aperture
  • area postrema
  • obex

The fourth ventricle has three openings:

  • Lateral apertures (aperturae laterales) or foramina of Luschka of the fourth ventricle located near the end of the lateral recesses.
  • Median aperture (apertura mediana) or foramen of Magendie lies caudally above the obex and opens to the cerebellomedullary cistern. Through these  three apertures cerebrospinal fluid leaves the ventricular system and enters to the subarachniod space.

Nuclei of the CN V to CN XII are located on the floor of 4th ventricle according to the following order:

  • Posteromedial column
    • Nucleus of abducent nerve  (nucleus nervi abducentis) – on the level of the facial colliculus
    • Nucleus of hypoglossal nerve  (nucleus hypoglosalis)
  • Anterolateral column
    • Nucleus ambiguus (nucleus ambiguus)  – in the medulla oblongata
    • Facial motor nucleus (nucleus nervi facialis) – in the pons
    • Trigeminal motor nucleus (nucleus motorius nervi trigemini) – in the pons.
  • Superior salivatory nucleus (nucleus salivarius superior) – in the pons for CN VII.
  • Inferior salivatory nucleus (nucleus salivarius inferior) – in the medulla oblongata for CN IX.
  • Dorsal motor nucleus of vagus (nucleus dorsalis nervi vagi).
  • Somatosensory:
    • Nuclei of trigeminal nerve,
    • Nuclei of spinal tract (CN V)
  • Special sensory:
  • Cochlear nuclei
    • Vestibular nuclei
    • Parasympathetic afferent
  • Nucleus of the solitary tract (for CN VII, IX, X)

Cerebrospinal fluid, subarachnoid space, and circumventricular organs

Subarachnoid space – between arachnoid and the pia mater is surrounding the spinal cord.

There are the following arachnoid cisternes:

  • cerebellomedullar cisterne
  • pontine cisterne
  • interpeduncular cisterne
  • lumbar cisterne

The cerebrospinal fluid is produced (secretion) within choroid plexus of all ventricles:

  • choroid plexus of lateral ventricle
  • choroid plexus of third ventricle
  • choroid plexus of fourth ventricle

Reabsorption of the cerebrospinal fluid takes place in arachnoid granulations.

Clinical comments

At the end of spinal cord on the level vertebra L1-L2 there is the subarachnoid cystern – the lumbar cystern. This is the favored place for sampling cerebro-spinal fluid.

The choroid plexus is:

  • l – Shaped for the lateral ventricle
  • v – Shaped for 3rd ventricle
  • M – Shaped for lateral ventricles and 3rd ventricle,
  • P – Shaped for the 4th ventricle

Circulation of the cerebrospinal fluid is according to the following scheme (flow from top to bottom)

  1. 1st and 2nd ventricle (lateral ventricle)
  2. Interventricular foramina
  3. 3rd ventricle
  4. Cerebral aquaeduct
  5. 4th ventricle
  6. Lateral aperture and median aperture of 4th ventricle
  7. Subarachnoid space
  8. Arachnoid villi
  9. Superior sagittal sinuses of dura mater

Subarachnoid cisterns:

  • Posterior cerebellomedullary cistern (cisterna magna)
  • Lateral cerebellomedullary cistern
  • Cistern of lateral cerebral fossa
  • Chiasmatic cistern
  • Interpeduncular cistern
  • Cisterna ambiens or ambient cistern
  • Pericallosal cistern
  • Paontocerebellar cistern
  • Cistern of lamina terminalis
  • Quadrigeminal cistern or cistern of great cerebral vein
  • Lumbar cistern

The circumventriclar organs are formed by neurons and specialized glia cells abutting fenestrated capillaries which are close to the ventricular system.

The circumventriclar organs:

  1. Median eminence is a small swelling shows by tuber cinereum immediately behind the infundibulum
  2. Neurohypophysis
  3. Vascular organ of the lamina terminalis
  4. Subfornical organ
  5. Subcommisural organ
  6. Pineal gland synthesizes melatonin which implicated in the sleep-wake cycle

Area postrema in the roof of the 4th ventricle at the level of the obex. It is the chemoreceptor trigger zone or vomiting (emetic) centre. It serves a protective function by reflex eliciting emesis via connections with hypothalamus and reticular formation. It contains neurons sensitive to a wide range of toxic substances.

Vascular organ of the lamina terminalis and subfornical organ complete a positive feedback loop and they are stimulated by the kidney secrets rennin in condition of the lowered blood volume which, on convertion to angiotensin II. They sent axons into the supraoptic and paraventricular nuclei of the hypothalamus and facilitate depolarization of neurons secreting ADH. 

Circumventricular organs.

Basal nuclei and related structures

Basal nuclei (BN) of the brain (nuclei basales) or basal ganglia (BG) are formed by grey matter of the telencephalon located below the cortex. The related structures of the BG are formed by the subthalamic nucleus (part of the diencephalon) and substantia nigra (part of the midbrain). BN are involved in the control of movement and they are involved in cognitive and emotional circuit. They form structures which are functionally closely related and they belong to the extrapyramidal system.

Traditional concepts of the basal ganglia.

The claustrum (claustrum) is a thin sheet of a grey matter between the external capsule and the extreme capsule (see below). Medially bordered by the putamen and laterally by the insula. It is connected with the cortex.

The caudate nucleus (nucleus caudatus) – is an arcuate shape mass of a grey matter between the lateral ventricle and internal capsule.

It consists of:

Head of caudate nucleus (caput nuclei caudati) is located anteriorly, it forms the lateral wall of the lateral ventricle and bordered its anterior horn.

Body of caudate nucleus (corpus nuclei caudati) is lying above thalamus and it  is located  in the inferior wall of the central part of the lateral ventricle.

Tail of caudate nucleus (cauda nuclei caudati) in the inferior horn of the lateral ventricle, laterally to the lateral geniculate body.

The lentiform nucleus (nucleus lentiformis) is shaped like the superior half of a biconvex lens. It arises partly from forebrain and partly from interbrain.

  • Anteriorly it is connected with:
    • Head of the caudate nucleus
    • Anterior perforate substance
  • Posteriorly it is connected with:
    • White substance and formes the peduncular loop (ansa peduncularis)
    • Amygdaloid body
    • Innominate substance
    • Nucleus basalis Meynerti – cholinergic neurons

nucleus basalis Meynerti – cholinergic neurons

The lentiform nucleus consists of:

  • medial portion called globus pallidus (globus pallidus) is connected with the internal capsule.
  • lateral portion called putamen (putamen)laterally bordered by the external capsule.

The lentiform nucleus is separated by the two bundles of the white matter:

  • External medullary lamina (lamina medullaris lateralis) separates the globus pallidus and putamen.
  • Internal medullary lamina (lamina medullaris medialis) separates the medial and lateral parts of the globus pallidus.

The putamen + the caudate nucleus = the striatum (striatum).

Relations of the basal ganglia and capsules: A. – Putamen, B.- Globus pallidus.

The capsules is a broad band of white fibres, which separates basal nuclei.

There are three following capsules:

The Internal Capsule (IC) (capsula interna) on the horizontal section looks like the mathematical symbol showing greater than (>) for the left hemisphere, or less than (<) for the right one. The internal capsule extends between cortex (corona radiata) and cerebral crus.

The internal capsule is composed of three parts:

The Anterior limb of IC (crus anterius capsulae internae) divides the head of the caudate nucleus (anteriorly) and the lentiform nucleus. It is visible on the transverse section, on the level f thalamus.

It contains:

  • Anterior thalamic radiation
  • Frontopontine fibres (Arnolds fascicle)

The Genu of IC (genu capsulae internae) separates the thalamus and head of caudate nucleus and the lentiform nucleus.

It contains the corticonuclear tract.

Posterior limb of IC (crus posterius capsulae internae) divides the thalamus, hypothalamus (inferiorly) and lentiform nucleus (laterally).

It contains:

  • Central thalamic radiations (corticothalamic and thalamocortical fibres)
  • Corticoreticular fibres
  • Corticorubral fibres
  • Corticospinal fibres
  • Corticothalamic fibres
  • Parietopontine and occipitopontine fibres
  • Thalamoparietal fibres

The pathway of the internal capsule.

The internal capsule accommodates to the medial surface of the lentiform nucleus. It consists of:

the retrolentiform part (pars retrolentiformis) is situated posterior to the lentiform nucleus.

It consists of the:

Retrolentiform part (pars retrolentiformis) is situated posterior to the lentiform nucleus. It consists of the:

  • Occipitopontine fibres
  • Occipitotectal fibres
  • Optic radiation (the composition of fibres radiating from lateral geniculate body towards the occipital lobe)
  • Posterior thalamic radiation

Sublentiform part (pars sublentiformis) is situated below the lentiform nucleus. It consists of the:

  • Acoustic radiation (the composition of fibres radiating from medial geniculate body towards the transverse temporal gyrus)
  • Corticotectal fibres
  • Temporopontine fibres
  • Corticothalamic fibres
  • Optic radiation

The pyramidal pathway is formed by corticospinal and corticonuclear fibers.

The corticospinal tracts provide fibers from the motor cortex through the corona radiata, posterior limb of IC (the most anteriorly are fibres for neck muscles, posteriorly to the leg and the urinary bllader), the crus cerebri, the pons, the medulla oblongata to the spinal cord. 

The corticonuclear tracts provide fibers from the cortex (inferior part of the precentral gyrus) to the nuclei of the cranial nerves. They pass through the corona radiata to the genu of IC.

The most anteriorly are fibers to the:

  • Eyeball muscle – CN III, IV, VI,
  • Laryngeal and palatine muscles – CN IX, X,
  • Masseter muscles – CN V,
  • Tongue muscles – CN XII,
  • Facial muscles – CN VII,
  • Neck muscles – CN VII, XI.

Anterior limb of IC:

  • Proximal and distal medial striate arteries (ACA).
  • Proximal and distal lateral striate branches of lenticulostriate arteries (anterolateral central) branche off MCA – globus pallidus, putamen, head and tail of caudate nucleus, genu and posterior part of anterior limb of IC.

Genu of IC:

  • Branches to genus of internal capsule of anterior choroidal artery (ICA).

Posterior limb of IC:

  • Branches to posterior limb of internal capsule of anterior choroidal artery branch of ICA.
  • Branches to retrolentiform part of internal capsule.

Clinical comments

The lenticulostriate arteries are the end arteries. The regions that they supply do not have significant collateral blood vessels. They occlusion give a stroke syndromes. The hemorrhage of these arteries may remain localized to putamen, involve the IC or may rupture into the ventricular system. Lacunar infarcts may have a serious functional consequences:

  • contralateral weakness.
  • contralateral loss of the pain & temperature sensation.
  • contralateral hemiparesis & presented of the Babinski’s sign (dorsiflexion of great toe).
The branches of the anterior choroidal artery.

The external capsule (capsula externa) is located laterally and it separates  the putamen from the claustrum.

The extreme capsule (capsula extrema) is situated laterally to the internal and external capsules and it divides the claustrum and insula.

The striatum gets fibres from the:

  • Thalamus (centromedian nucleus) and forms the thalamostriatal tract.
  • Cortex (motor area) forms the corticostriatal tract.
  • Substantia nigra (fibres with neurotransmitter – dopamine) formes the nigrostriatal tract.

It sends fibres to the:

  • Globus pallidus.
  • Substantia nigra (fibres with neurotransmitter – GABA).
The connections of the striatum.

Clinical comments

Corpus striatum lesions gives: Sydenham’s chorea, and/or Hungtinton’s chorea (caudate nucleus).

Hyperkinetic disorders:

Hemibalizm is the effect of the subthalamic nucleus lesion usually as the results of the cerebrovascular accident in this region. It gives the following clinical feature:

  • Violent, involuntary movement of wide excursion confined to one half of the body.

Corpus striatum lesions gives:

  • Sydenham’s chorea
  • Hungtinton’s chorea (caudate nucleus)

The globus pallidus (GP) gets fibres from striatum and subthalamic nucleus. The GP sends fibres to:

  • Thalamus (anterior ventral nuclei) and forms ansa lenticularis and fasciculus lenticularis which gives fasciculus thalamicus – the medial part of GP.
  • Subthalamic nucleus forms the fasciculus subthalamicus – the lateral part of GP.
  • Substantia nigra and forms the pallidonigral tract.
  • Habenula and forms the pallidohabenular tract.
The connections of the globus pallidus.

From the lateral portion of globus pallidus (GP) under the internal capsule goes the leticular loop, Its fibers sweep ventromedially and rostrally around the posterior limb of the internal capsule & enters Forel’s field H.

The Field H split into:

Field H1 formed by the thalamic fascicule and include:

  • Pallidothalamic tract
  • Dentatothalamic tract
  • Medial lemniscus

Field H2 formed by the lenticular fascicule. It goes from medial part of GP and  

perforate internal capsule enters Forel’s field H2.

The connections of the substantia nigra.

The lesion of the nigrostriatal tract and the degeneration of dopamine neurons primarily in substantia nigra increases level of dopamine and gives Parkinson’s disease.

Parkinson’s disease manifests by the disturbances in the motor system and it gives the following clinical features:

Positive symptoms:

  • Resting tremor (“pill-rolling”)
  • Muscular rigidity, cogwheel rigidity
  • Involuntary movements
  • Absence of spontaneous gesturing

Negative symptoms:

  • Hypokinesia (akinesia)
  • Bradykinesia, slowness of movement esp. difficulties in initiation and cessation of movement
  • Postural disturbances, Parkinson’s posture
  • Cognitive impairments
  • Mask-like facies

Clinical comments

The dopamine takes a great role in the following neuropsychiatric disorders:

  • Parkinsons disease
  • Attention deficit hyperactivity disorder (ADHD)
  • Schizophrenia
  • Paranoid psychosis

The surgical treatment of Parkinson’s disease is the lesion of the GP, lenticular loop or ventral nuclei of the thalamus. The dopamine deficiency sometimes can affects the non-motor functions as apathy, depression, schizophrenia (disorder modulation of prefrontal circuits). The dopamine deficiencies sometimes can affects the non-motor functions as apathy, depression, and schizophrenia (disorder modulation of prefrontal circuits).

The schizophrenia is connected with the hypersensitive receptors of dopamine in the limbic system.

The positive syndromes of schizophrenia are as follow:

  • Hallucinations
  • Delusion

The negative symptoms are the:

  • Flattend affect
  • Cognitive deficit

Clinical comments

Amphetamine and cocaine enhance dopamine transmission and can produce paranoid psychosis.

Effective blocking of the effects of dopamine are the mechanism of some of the most effective anti-schizofrenic drugs. The large dose of amphetamines, which cause over-release of dopamine, could potentially cause schizophrenia.

Amygdaloid body

The amygdaloid body (corpus amygdaloideum) – located between the temporal pole and the inferior horn of lateral ventricle. It is connected with some autonomic functions.

Amygdaloid body consists of two parts:

  • Corticomedial part consists of medial amygdaloid nucleus, central amygdaloid nucleus and cortical amygdaloid nucleus.
  • Basolateral part consists of basomedial and basolateral amygdaloid nuclei and lateral amygdaloid nucleus.

Amygdaloid body connects with:

  • Olfactory bulb
  • Hypothalamus and pre-optic area (through stria terminalis)
  • Thalamus
  • Reticular formation
  • Hippocampus
  • Cortex of frontal and temporal lobes

Dysfunction of amygdala results in autism.


Rhinencephalon (rhinencephalon) and olfactory pathways are the oldest parts of the grey matter of the forebrain. It controls human behaviour.

The olfactory lobe or brain (lobus olfactorius) or peripheral rhinencephalon contains:

Olfactory bulb (bulbus olfactorius) is an enlargement of the arising of the olfactory tract, in the anterior part of the olfactory sulcus.

Olfactory tract (tractus olfactorius) which is a connection between olfactory bulb and olfactory trigone.

Olfactory trigone (trigonum olfactorium) which is the widened triangular end of the olfactory tract.

Medial and lateral olfactory striae (striae olfactoriae medialis et lateralis) which are  diverging bundles /fibres/ of the olfactory tracts radiating fanlike at the olfactory trigone.

Anterior perforated substance (substantia perforata anterior) – is a perforated area behind the olfactory trigone. It is the place for the small cerebral vessels.

Semilunar gyrus (gyrus semilunaris) and ambiens gyrus (gyrus ambiens) formed the primary olfactory cortex. Central rhinencephalon or limbic lobe (see below).

The limbic lobe (lobus limbicus) is located around diencephalons. It has two portions:

Externals portion contains:

Subcallosal area (area subcallosa) is a field below the rostrum and genu of the corpus callosum located at the medial surface of the frontal lobe.

The cingulate gyrus (gyrus cinguli) is a convolution between sulcus of corpus callosum and cingulate sulcus. It receives inputs from the anterior thalami nuclei and gives fibers to parahippocampal gyrus.

The cingulate gyrus has:

  • isthmus of cingulate gyrus (isthmus gyrus cinguli) which is a reduction at the passage of the cingulate gyrus into the parahippocampal gyrus.

The cingulate sulcus (sulcus cinguli) which is located at the anterior and superior portion of the cingulate gyrus.

The parahippocampal gyrus (gyrus parahippocampalis) is a convolution of the parahippocampal sulcus with its termination:

  • uncus (uncus) hook-shaped ending of the parahippocampal gyrus.

The parahippocampal sulcus (sulcus parahippocampalis) which is located between parahippocampal gyrus and dentate gyri. It meets the uncus.

The septal region includes the paraterminal and subcallosal gyrus and their nuclei: dorsal, lateral and medial septal nuclei.

External portion of the rhinencephalon.

The internal portion contains the hippocampus (see below).

Hippocampus (hippocampus) – “Neptune’s sea-horse” was the name given to it by  the anatomists of the Middle Ages (ancient Greeks described it in mythology as sea-horses without the heads).

The Hippocampus is described as grey matter of the lateral part of the parahippocampal gyrus (without the fornix). It forms a curved elevation extending through the floor of the inferior horn of the lateral ventricle.

It contains:

  • Pes of hippocampus (pes hippocampi) – a paw-like termination of the hippocampus.
  • Fimbria of hippocampus (fimbria hippocampi) is a continuation of the crus of the fornix.
  • Subiculum (subiculum) from the parahippocampal gyrus.
  • Alveus of hippocampus (alveus hippocampi) is slender white matter of the hippocampus.
  • Indusium griseum (indusium griseum) which is a thin layer of the grey matter around the superior surface of the corpus callosum.
  • Gyrus fasciolaris (gyrus fasciolaris) which forms a junction between the longitudinal striae and dentate gyrus and the indusium griseum dentate gyrus (gyrus dentatus) which is a convolution of palium.

It is believed that structures like septum pellucidum, fornix and amygdaloid body belong to limbic lobe too. The limbic lobe connects with the parts of hypothalamus, thalamus and olfactory lobe.

The new concept of the limbic system.

Diencephalic Areas of Limbic System are formed by:

Thalamus – the thalamic nucleus projects to cingulates gyrus

  •  Anterior nuclei,
  • Mediodorsal or dorsomedial nucleus of the thalamus – projects to the frontal cortex (orbital and medial part),
  • Midline nuclei.
  • Preoptic region – preoptic periventricular nucleus, medial preoptic nucleus
  • Supraoptic region – suprachiasmatic nucleus
  • Anterior nucleus of hypothalamus (receives input from the mammillary nuclei)
    • Supraoptic nucleus
    • Paraventricular nucleus
    • Tuberal region – dorsomedian nucleus
    • Ventromedial nucleus
    • Infundibular (arcuate) nucleus

Epithalamus – medial and lateral habenular nucleus

Mammilary region – lateral, medial and intermidiate mammilary nucleus. Mammilary nuclei gets fibers from the hyppocampal formation (subiculum) through fornix and also from tegsmental and raphe nuclei.

The limbic midbrain area consists of the:

  • Median raphe nucleus called also as the superior central nucleus
  • Ventral tegmental area
  • Dorsal tegmental area
  • Periaquedactal gray matter

The septal region, the hypothalamus and the limbic midbrain area form the septo-hypothalamo-mesencephalic continuum. It is connected with emotions and their expression.

The hippocampal rudiments if formed by the:

  • Fasciolar gyrus (gyrus fasciolaris)
  • Indusium griseum

The hippocampal formation is formed by hippocampus proper with its 4 areas, dentate gyrus and subiculum. The hippocampal formation has 3 layers of archicortex.

The hippocampus proper is formed by:

  • Molecular layer
  • Pyramidal layer
  • Multiform or polymorphiclayer

Dentate gyrus has the following layers:

  • Molecular layer
  • Granular layer
  • Multiform or polymorphic layer

The subiculum is a transitional structure between the archicortex and the entorhinal cortex. The entorhinal cortex belongs to the paleocortex.

The structures of the hippocampal formation.
  • The hippocampus proper forms the Cornu Ammoni (CA). The CA has 4 different areas because of the differences in cell morphology (CA1, CA2, CA3, CA4).
  • The CA1 area is the most sensitive for insufficientia and it is called as the Sommer area.
  • The CA4 area is called as the area dentate.  
The areas of the cornu ammoni.
The structures of the limbic systems S – septal region, PO – preoptic region, LMA – limbic midbrain area.

Tracts of limbic lobe consist of internal and external pathways.

Internal tracts connect parts of the limbic lobe. Fibers extend from hippocampus and form fornix (crus, commissure of fornix and body of fornix). They divide into precommissural fibres (pass to septum pellucidum) and postcommissural fibers  (pass to mammilary bodies, nuclei of hypothalamus, hypophysis, anterior and medial nuclei of thalamus, tegmentum and   reticular formation in pons and medulla oblongata. 

External tracts connect the limbic lobe with the diencephalons and nuclei of the reticular formation. They mainly  pass to the medial nucleus of the thalamus, anteroventral nucleus of thalamus, intralaminar nuclei of thalamus, habenular nuclei and nuclei of hypothalamus. The limbic lobe has some connections with the frontal lobe. 

The olfactory  lobe deals with the sense of smell.

Papez (1930) hypothesized that enthorinal cortex, hippocampal formation, cingulated gyrus, mammilary body and thalamus are interconnecting and form a loop called as the Papez circuit. It controls emotions. Lesion of any part of the Papez circuit gives disorders of to this affect. 

Clinical comments

The Alzhaimer Disease is induce by hippocampal neurons lesion mainly in the CA1 area, subiculum and II, IV layer of the enthorinal cortex. Its manifestation is causes problems with short-term memory.

The Epilepsy is induced by the lesion of the hippocampus and the amygdaloid body.

Papes’ circuit

The mammilothalamic fibres run from the mammilary body to the anterior nuclei of the thalamus.

It was discovered that there are pleasure centers (cingulate gyrus, hipoccampus, septum pellucidum, amygdaloid body) and punishment centers (hypothalamus, thalamus and tegmentum) in the limbic lobe.

The limbic system deals with the experience of moods, emotions, and consolidation of working, short-term (seconds) into the long-term (hours to decades) memory through intermediate term (minutes) memory.

There are different types of the memory:

  • Declarative memory (remembering facts)
  • Spatial memory (remembering location)
  • Procedural memory (remembering how to do the things)
  • Motor memory (motor skills)

It is a dopaminergic neural pathway. The loop starts in the prefrontal cortex (inferior part), next it passes through the nucleus accumbens (the anterior part of the striatum) and pallidum (ventral part), It returns to the prefrontal cortex through the mediodorsal nucleus of the thalamus.

Function: It is responsible for emotions as the part of the motor expression – gesteruring posture like smiling, submissing or even aggressive.

Dysfunction: Its lesion gives the symptoms characteristic for Parkinsons disease or dementia. It is a lack of spontaneous gesturing and face looks like mask without any expression.

Loop between the limbic system and basal ganglia.

Spinal Cord

The spinal cord (medulla spinalis) is located in the vertebral canal and it is extended between the pyramid decussation and the conus medullaris with filum terminale.

The spinal cord connects with the medulla oblongata of the brainstem near the superior border of the atlas, just below the foramen magnum.

The conical caudal end of  the spinal cord is known as the conus medullaris (conus medullaris). It is at the level of the inferior border of the first lumbar vertebra and superior border of the second lumbar vertebra.

The spinal cord has 31 pairs of spinal nerves, each of which is associated with a successive region of the spinal cord by the dorsal and ventral roots. The abbreviations C, T, L and S indicate segments of the spinal cords. Because of the differential growth of the vertebral column and spinal cord during development, the more caudal segments are located higher in comparison to parts of  vertebral column,  (e.g. twelfth thoracic segment lies opposite the tenth thoracic vertebra).

The dorsal and ventral roots of the lower lumbar, sacral and coccygeal nerves are long and are named cauda equina (cauda equina) – a horse tail.

The spinal cord contains five parts:

  • Cervical segments C1 – C8
  • Thoracic segments Th1 -Th12
  • Lumbar segments L1 – L5
  • Sacral segments S1 – S5 
  • Coccygeal segments Co1
The Central Nervous System and the morphology of the spinal cord.

The spinal cord has two enlargements:

  • Cervical
  • Lumbar or lumbosacral

The funiculus is a longitudinally organized structure of the external white matter of the spinal cord and divides into three regions (columns):

Anterior funiculus – between the anterior median fissure and the anterolateral sulcus called Anterior Root Entry Zone – AREZ.

Lateral funiculus – between the anterolateral sulcus and the posterolateral sulcus.

Posterior funiculus – between the posterolateral sulcus called Posterior Root Entry Zone – PREZ and the posterior median sulcus.

It contains (in the cervical part):

  • Gracile  fasciculus (fasciculus gracilis) located medially
  • Posterior intermediate sulcus (between gracile fasciculus and cuneate fasciculus is located)
  • Cuneate  fasciculus (fasciculus cuneatus) located laterally

Columns are longitudinally organized structures of the internal part of the spinal cord (grey matter) which divide into three parts:

  • Anterior column
  • Lateral column (only C8-L2, L3)
  • Posterior column

There are two ways of describing grey matter in spinal cord . We can recognize nuclei and spinal laminae.

On the cross section the grey matter can be divided into (H-shaped area of grey matter like a butterfly):

Anterior horn with motor overflow contains nuclei which contain motor neurons (spinal laminae VII – IX):

  • Anteromedial and posteromedial nuclei – they supply muscles of trunk.
  • Anterolateral, posterolateral  and retroposterior lateral nuclei – they supply muscles of limbs.
  • Central nucleus – it is seen in cervical part and contains nucleus of phrenic nerve.
  • Nucleus of accessory nerve – in the cervical part.

Posterior horn with sensory processing  (spinal laminae I – VI) contains (going centrally) apex, head, neck and base of posterior horn. Between apex and external surface there are marginal zona and gelatinous substance – both are important in conducting pain stimuli. Posterior horn contains nucleus proprius. Axons of this nucleus form afferent pathways (somatosensory). Besides posterior horn contains thoracic nucleus which form dorsal spinocerebellar tract.

Intermediate grey matter, which consist of central and lateral intermediate grey substance. Lateral grey matter is especially developed in thoracic part and form lateral horn. There are present nuclei (spinal laminae VII):

  • Intermediolateral nucleus (sympathetic C8 – L2, L3)
  • Intermediomedial nucleus (parasympathetic S2 – S4)

Central canal

Central canal is a part of ventricular system which is present in the spinal cord. It is surrounded by grey matter (anterior and posterior grey commisures) and white commisure.

Conus medullaris contains terminal ventricle.

The roots of the spinal nerves are:

  • Anterior – in the anterolateral sulcus
  • Posterior – in the posterolateral sulcus
Internal and external structures of the spinal cord.

Spinal meninges

The spinal cord is enveloped by three meninges. These membranes are continuous with the cranial meninges. The meninges of the spinal cord are described from the outside-in direction:

The spinal  dura  mater  is  separated  from  vertebral  periosteum  by extradural (epidural) space.

The spinal arachnoid mater  lines  the  spinal  dura  mater. It has:

  • Arachnoid trabecule – linking to the pia mater.
  • Denticulate ligament (ligamentum denticulatum) anchors the spinal cord to arachnoid and through it to the dura mater.

The spinal pia mater – covers the whole of the spinal cord and lines its anterior median fissure.

The subarachnoid space is located between arachnoid and the pia mater and surrounds the spinal cord and brain.

Clinical comments

At the end of spinal cord L1 – L2 there is the subarachnoid cistern – the lumbar cistern. This is the most favourable place for sampling of cerebrospinal fluid.

The spinal cord is supplied by:

Anterior spinal artery arises from each the vertebral artery within the skull and then two anterior spinal arteries join and form one blood vessel It passes into the ventral median fissure and there receives segmental branches from the ascending cervical artery, posterior intercostal artery, lateral lumbar arteries (these branches are called radicular arteries) and also from branches of the vertebral artery.

It gives off:

  • Sulcal arteries which supply the spinal cord segmentally.

Posterior spinal artery is branch of vertebral artery and supplies the dorsal part of the spinal cord. Posterior spinal arteries don’t form one blood vessel.

It also receives segmental support from the many segmental branches (radicular arteries).

Radicular arteries divide into two branches: anterior (connecting with ventral spinal artery) and posterior (connecting with dorsal spinal artery). These arteries accompany the roots of the spinal nerves.

Vasocorona artery  connects segmentally the anterior spinal  artery with posterior spinal artery.

All veins accompany corresponding arteries of the spinal cord.

Anterior spinal vein located at the anterior fissure. It receives blood from the segmental veins – sulcal veins which receive from anteromedial part of the spinal cord.

Posterior spinal vein situated at the posterior fissure.

Posterolateral spinal veins located on the posterior surface laterally to the posterior spinal vein which drains the posterior funiculus and posterior horns.

Venous vasocorona which connects segmentally the anterior spinal vein with the posterolateral spinal veins and the posterior spinal vein.

Pathways of the Central Nervous System

Information entering the CNS is employed in the reflex, autonomic and unconscious ways, only a small amount reaches consciousness.

The pathways of the CNS are arranged so that each cerebral hemisphere controls muscles of the opposite or same half of the body and receives information from the opposite or same side.

Organisation of the Pathways of the CNS

Axons run for variable distances within the spinal cord and the brain. Most axons are short intrasegmental or intersegmental tracts, but many run for long distances joining the brain and the spinal segments.

Short intrasegmental & intersegmental fibres which lie close to the grey matter of the spinal cord (fasciculus proprius).They are present in all funiculi and form anterior, posterior and lateral proper fasciculi.

The jerks are examples of proper spinal cord activity. They contain at least 2 or more neurons. There are examples of jerks: knee jerk, ankle jerk, biceps jerk, elbow jerk, supinator jerk.

Ascending fibres which lie in the posterior column and the periphery of the lateral column of the spinal cord

Descending fibres which lie in the anterior column and the intermediate part of the lateral column of the spinal cord.

The efferent pathways form the motor pathways. They are called as:

The pyramidal pathways are connected with the voluntary movement. They have 2 neurons: the upper & lower motor neurons. 

The pyramidal pathways are divided into the:

  • Lies in the lateral funiculus.
  • Is crossed on the level of pyramidal decussation.
  • Terminates in interneurons of anterior horn L VII.
  • Includes fibers controlling the trunk and muscle and proximal joints.
  • Lies in the anterior funiculus.
  • Is uncrossed or cross at segmental level.
  • Terminates mostly in laminae VII.
  • Includes fibers controlling the trunk and muscle and proximal joints.
Anterior and lateral corticospinal tracts.

Origin: Cerebral Cortex, the pyramidal cells (mostly), fibers arise from the UMN, the 1st neuron pass through:

  1. Corona radiata
  2. Posterior limb of internal capsule
  3. Crus cerebri (middle portion)
  4. Longitudinal pontine fiber
  5. Pyramidal decussation of pyramid (the most of the fibers decussate just below the junction the medulla)
  6. Lateral corticospinal tract
  7. Pyramid
  8. Anterior corticospinal tract

Termination: grey matter of spinal cord – anterior horn (spinal laminae VII -IX).

The corticospinal tract

The corticobulbar fibers projecting to cranial motor nuclei in the lower brainstem:

  • GSE – hypoglossal (XII), abducens (VI), trochlear (IV) and oculomotor (III) nucleus
  • SVE – ambiguus (IX, X, XI), facial motor (VII), trigeminal motor (V) nucleus
  • Nucleus gracilis and cuneatus
  • Trigeminal sensory nucleus
  • Solitary tract nucleus

Reticular formation (corticoreticular fiber).

Largely bilateral fibers, which go into:

  • laryngeal, pharyngeal, palatal and upper facial muscles
  • muscles of mastication and extraocular muscles

Unilateral fibers, which go into:

  • lower facial muscle (facial palsy) and muscles of tongue

The sternocleidomastoid (SCM) and trapezius (uncrossed) – spinal accessory

The pseudobulbar Palsy – syndrome of bilateral UMN lesion

Clinical comments

LMN syndrome (LMNS) – involves direct damage to motor neurons that innervate muscles as clinical examples – poliomyelitis. Demonstrates “LOWER” “activity” as HYPOtonia.

UMN syndrome (UMNS) – damage to any descending pathway of the motor system. Demonstrates “INCREASED” “activity” as HYPERtonia.

Definitions of most common terms:

  • Atonia – lack of tone.
  • Dystonia – diskinetic (distorted/impaired) movement due to disordered tonicity of muscle.
  • Hypotonia (flaccidity) – greatly reduced tone.
  • Hypertonia (rigidity or spasticity) – greatly increased tone.
  • Paralysis – inability to effect voluntary movement.
  • Paresis – incomplete or partial paralysis.
  • Fibrillations – spontaneous contractions of single muscle fibers.
  • Fasciculations – spontaneous contractions of groups (fasicles) of muscle fibers.


LMN vs. UMN lesion effects

In a LMN lesion, everything goes down: strength, tone, reflexes, muscle mass, and the big toe down in plantar reflex – STORM Baby tells you effects:

  • Strength
  • Tone
  • Other
  • Reflexes
  • Muscle mass
  • Babinski’s sign (Babinski’s sign is big toe up: toe up = UMNL)
Pyramidal pathway and associated circuits.

The extrapyramidal system deals as assistant for pyramidal system and it is responsible for maintaining of body balance, tone of muscles and automatic movements. Besides it cooperates with autonomic nervous system and somatosensory part of cortex.

This system has obvious cerebellar connections too. Extrapyramidal system is the name given to the groups of fibres passing:


  • motor cortex (posterior parts of frontal gyri: the superior –  centre of complex trunk movements, middle – centre of coordination for head and eyeballs movements and inferior – (motor speech area)


  • Subcortical nuclei (which are found the basal nuclei)
  • Striatum (centre of muscle tone and automatic movments)
  • Subthalamus of the forebrainsubthalamic nucleus (responsible for balancing movements of limb)
  • Substantia nigra (responsible for coordination of fast involuntary movements)
  • Red nucleus (responsible for coordination of centres of extrapyramidal system with cortex, cerebellum and vestibular nuclei)
  • Nuclei of the reticular formation and vestibular nuclei


  • Lower motor neurons.

Tracts of extrapyramidal system are multineuronal pathways. There are following efferent and afferent fibres between different structures:

  • afferent fibres – from cortex, substantia nigra and thalamus
  • efferent fibres – to globus pallidus and substantia nigra
  • afferent fibres – from striatum and subthalamic nucleus
  • efferent fibres – to thalamus, subthalamic nucleus, reticular formation (tegmentum), olivary nuclei
  • afferent fibres – from striatum, putamen and frontal cortex
  • efferent fibres – to striatum and thalamus
  • afferent fibres – from contralateral dentate nucleus,  ipsilateral and contralateral superior  colliculus, globus pallidus and ipsilateral frontal cortex
  • efferent cortex – rubro-spinal, rubro-reticular and rubro-olivary tracts

The most important efferent tract of extrapyramidal system is central tegmental tract which passes to olivary nucleus and consists of rubro-olivary, rubroreticulary tract and pallidoolivary tract. Then fibres pass to cerebellar cortex through olivocerebellar tract. Fibres from parts of extrapyramidal system pass to spinal cord and influence motor activity. The main descending pathways are the rubroreticulospinal and vestibulospinal tracts.

Rubrospinal tract originates in the midbrain (red nucleus), next it crosses its fibers in ventral part of tegmental decussation, and goes down anteriorly to the lateral corticospinal tract.

Tectospinal tract originates in the superior colliculus and form the medial longitudinal fasciculus which goes through the medulla. Its fibres cross in the raphe region and next they finished in the cervical segments. It ends as anteromedial part of the anterior funiculus.

Vestibulospinal tract originates in the lateral vestibular nuclei after runs in the anterior part of lateral funiculus.

Reticulospinal tracts origin in pons & medulla, they go ipsilaterally in anterior funiculus.

Autonomic systems: diffuse projections of tegmental nuclei containing mostly aminergic transmitters (raphe ncl.: serotonin, locus coeruleus: norepinephrin); visceral nuclei in the medulla project to sympathetic and parasympathetic nuclei of the spinal cord.

Nuclei: raphe nuclei

Location: midline continuous column

5-HT path

  • Some fibers terminate in substantia gelatinosa (part of central pain control system)
  • Some fibers terminate in intermediolateral cell column
  • Ascending fibers involved in sleep-wake cycles (­ activity when awake)
  • Ascending fibers involved in affective behavior (depression)
  • Cause vasoconstriction of cerebral blood vessels (drugs blocking this – migrane)

Nuclei: locus ceruleus

Location: pontine & medullary reticular formation

NE path

  • role in sleep wake cycle, increased attention/vigilence

Nuclei: substantia nigra (pars compacta) & ventral tegmental area

Location: Midbrain

DA path

  • output to striatum (caudate and putamen) nigrostriatal path
  • output to septum, amygdala, frontal lobe

Upper motor neurons (UMNs) are located in the cortex:

  • Primary Motor Area
  • Premotor Area
  • Paracentral Lobule
The motor homunculus of the precentral gyrus.
The motor pathways of spinal cord . The transverse section.

Lower motor neurons (LMNs) are located in:

  • Anterior horn of the spinal cord (cervical, thoracic, lumbar or sacral part). The LMN gives:
    • Axons, the anterior roots which forms the spinal nerve.
    • Terminal axons as the neuromuscular junction.
  • Brain stem whose passes axon to the motor plates of striated muscle.

Locations of the LMN of the pyramidal pathways:

  • Anterior horn cell of the spinal cord
  • General Somatic Efferent (GSE) nuclei
    • Hypoglossal nucleus (CN XII)
    • Abducens nucleus (CN VI)
    • Trochlear nucleus (CN IV)
    • Oculomotor nucleus (CN III)
  • Special Visceral Efferent (SVE) nuclei
    • Ambiguus nucleus (CN IX, X, XI)
    • Facial (motor) nucleus (CN VII)
    • Trigeminal motor nucleus (CN V)
Pyramidal and extrapyramidal pathways connections.

  1. Corticospinal tract carries information for voluntary, discrete and skilled movement.
  2. Tectospinal tract fibres mediate reflexive head and neck movements in response to visual & vestibular stimuli.
  3. Rubrospinal tract control of tone muscle in distal part of flexor groups.
  4. Vestibulospinal tract have facilitatory effects on anti-gravity extensor muscles (reflex activity and muscle tone).
  5. Reticulospinal tracts act mostly on axial muscles of the neck and trunk for postural reflexes.

Lesion results in:

  • Paresis (e.g. paralysis) associated with (I)
  • Initial loss of muscle tone succeded by gradual increase of muscle tone in antigravity muscles, (II)
  • Hyperactive deep tendon myoctatic reflexes), (III)
  • Loss of superficial abdominal [cremaster] reflexes and (IV) the appearance of an extensor toe response (Babinski sign).

Centrally generated motor commands can alter the transmission of spinal reflexes; damage to the CNS produces characteristic alterations in reflex responses and muscle tone.

  • Interruption of descending pathways of the spinal cord frequently produces spasticity.
  • Transection of the spinal cord in humans leads to a period of spinal shock followed by hyperreflexia.
  • Injury to motor roots affects muscles including weakness, wasting, fasciculation, and loss of tendon reflexes.
  • Injury of descending tracts produce weakness, increased tendon reflexes, and spasticity in segments below the lesion.
  • Sensory symptoms:
    • Unilateral lesions (hemisection) result in anterolateral signs including loss of pain and temperature sensation on opposite side and loss of discriminative touch, vibration sense and position sense ipsilaterally below the affected segment – Brown-Séquard syndrome.
    • Polyneuropathy affects multiple peripheral nerves and involves predominantly cutaneous sensation loss in hands and feet. It is attributed to impaired axonal transport.
    • Basal ganglia (extrapyramidal) organize input from eyes, motor cortex and cerebellum.  Produce what we call “grace” and “skill”.

There are present some more pathways in spinal cord which belong to pyramidal and extrapyramidal tracts.

Pathways of the spinal cord – setting:

  • Anterior fasciculus proprius (proper tract)
  • Anterior corticospinal tract (pyramidal tract)
  • Lateral and medial vestibulospinal tracts (extrapyramidal tracts)
  • Reticulospinal fibres (extrapyramidal tract)
  • Pontoreticulospinal tract (extrapyramidal tract)
  • Interstitiospinal tract (extrapyramidal tract)
  • Tectospinal tract (extrapyramidal tract)
  • Olivospinal tract (extrapyramidal tract)
  • Anterior spinothalamic tract (somatosensory tract)
  • Posterior fasciculus proprius (proper tract)
  • Gracile fasciculus (somatosensory tract)
  • Cuneate fasciculus (somatosensory tract)
  • Lateral proper fasciculi (proper tract)
  • Fastigiospinal tract (extrapyramidal tract)
  • Lateral corticospinal tract (pyramidal tract)
  • Rubrospinal tract (extrapyramidal tract)
  • Bulboreticulospinal tract (extrapyramidal tract)
  • Olivospinal fibres (extrapyramidal tract)
  • Spinotectal tract (extrapyramidal tract)
  • Lateral spinothalamic tract (somatosensory tract)
  • Anterior and posterior spinocerebellar tracts (somatosensory tracts)
  • Dorsolateral tract
  • Spino-olivary tract (extrapyramidal tract)
  • Spinoreticular tract (extrapyramidal tract)
  • Hypothalamospinal tract (extrapyramidal tract)
  • Spinovestibular tract (extrapyramidal tract)
  • Trigeminospinal tract (somatosensory tract)
  • Impulses run from receptor cells.
  • In spinal nerve as the first neuron of cell bodies located in the dorsal root ganglion.
  • As the ascending branches to the posterior column (fibres from  the lower limb lie medially to those from the trunk, upper limb & neck).
  • To synapse in the gracile or cuneate nuclei of the medulla oblongata – the  2nd neuron
  • As the axons swing round the central grey matter,  cross  the  midline  and then ascend as a medial lemniscus to: 
    • The thalamus – ventral posterolateral nucleus – the 3rd neuron to:
    • The axons of the ventral posterolateral nuclei  ascend  through   the  internal capsule to the postcentral gyrus.
Structure of pathways for touch & pressure
General sensation from face – the trigeminothalamic tracts
  • Impulses run from receptor cells of pain & temperature to the trigeminal nerve.
  • By fibres to the trigeminal ganglion the 1st neuron to:
  • The central branches  entering  the  pons  and  descending  into  the  lower medulla as a spinal tract of the trigeminal nerve their fibres.
  • Synapse in the spinal nucleus of trigeminal nerve the 2nd neuron to:
  • The second set of axons that cross the midline, and join  the  spinal  lemniscus and end in the ventral thalamic nuclei to:
  • The 3rd nuron set of axons project to the lower part of the postcentral gyrus.
  1. Pathways for proprioceptive information may reach a conscious level (cerebral cortex) but most is utilised by the cord and cerebellum and nerve reaches consciousness. Unconscious proprioceptive fibres have their cell bodies in the dorsal root ganglion – the first neuron – and their impulses reach the cerebellum by one of three pathways:
  2. Branches of the 1st neuron may ascend in the posterior column of the spinal cord to:
  3. The lateral cuneate nucleus of the medulla – the 2nd neuron
  4. Fibres arising here pass in the ipsilateral inferior cerebellar peduncle to the vermis and anterior lobe of the cerebellum.
  • Spinothalamic Tracts
    • Anterior Spinothalamic Tract
    • Lateral Spinothalamic Tract
  • Spinoreticular or Spinoreticulothalamic Tract
Pathways for light touch
  1. Impulses run from receptor cells.
  2. In spinal nerve the first neuron of cell bodies in the dorsal root ganglion to:
  3. Synapse in the posterior horn of the spinal cord – the 2nd  neuron crosses  the midline through white commisure  and then ascends as the anterior spinothalamic tract  to:
  4. The thalamus – specifically the ventral nucleus the 3rd neuron.
  5. The axons of the ventral nuclei ascend through the internal capsule to the postcentral gyrus.
The anterior and lateral spinothalamic pathways
  1. Impulses run from receptor cells.
  2. In spinal nerve the 1st neuron – cell bodies in the spinal ganglion . The central fibres enter the spinal cord and  ascend for  the short distance in the dorsolateral tract.
  3. To synaps in the posterior horn of the spinal cord – the  2nd neuron – cross the cord in the  anterior grey commisure and then it forms the lateral spinothalamic tract and as the spinal lemniscus to:
  4. The thalamus – venteroposterior nucleus the 3rd neurons.
  5. The axons of the ventral nuclei ascend through the internal capsule.
  6. Termination: postcentral gyrus

The 1st neuron may synapse in the posterior horn of the gray matter.

2nd neuron – arising here crosses immediately and ascends in the anterior spinocerebellar tract to the vermis and anterior lobe of the cerebellum.

This is mainly crossed pathway.

The 1st neuron may synapse in the thoracic nucleus of the posterior horn of the gray matter.

2nd neuron – Arising here goes the to ipsilateral posterior spinocerebellar tract and thence trough the inferior cerebellar peduncle to the vermis and anterior and posterior lobe of the cerebellum.

This is mainly uncrossed pathway.

The sensory pathways of spinal cord.

Posterior funiculi arise mostly from medial bundle and carry epicritic mechanosensation for the lemniscal system (spinobulbar) and proprioceptive fibres terminating in the dorsal nucleus. The descending fibres form interfascicular fasciculus and septomarginal fasciculus; lower limb is represented in gracile fasciculus; trunc and upper limb in cuneate fasciculus;

The lesions give ataxia.

  1. Anterior spinothalamic tract is complete crossing; terminate in several nuclei of the brain stem tegmentum and the intralaminar nucleus of dorsal thalamus; carry information about “light touch” to glabrous skin and second, slow, burning pain (paeospinthalamic).
  2. Lateral spinothalamic tract terminate in thalamic ventral posterolateral nucleus; fibres are mostly, but not completely crossed; major clinical importance: sharp pricking pain and temperature (neospinothalamic).

Spinotectal tract: Crossed secondary fibres in anterolateral location terminate in deep layers of mesencephalic central gray matter and superior colliculus.

  1. Posterior spinocerebellar tract carries uncrossed fibres arising from the dorsal nucleus of Clarke-Stilling and is located in a posterolateral peripheral location; they form the posterior cerebellar peduncle and terminate in the spinocerebellum. Carry impulses from proprioceptive inputs from muscle spindles, exteroceptive impulses are also present e.g. mechanoreceptors from the foot pad.
  2. Anterior spinocerebellar tract in the periphery of the lateral funiculus originates from contralateral neurons (crossed), and forms the anterior cerebellar peduncle (crossing back).
  1. Spino-olivary tract: component of the spino-cerebellar pathway.
  2. Spinoreticular tract: component of the anterior spinothalamic tract (paleo-) portion.

Reflex Arches

  • Reflex arch (jerk) is the LMN activity through the monosynaptic pathways.
  • Deep tendon reflex (DTR) (knee jerk) is a monosynaptic reflex.
  • Patellar tendon – Stretch receptor to anterior horn cell
  • Quadriceps – Contraction

Increased DTR is characteristic sign of UMN syndrome.


Reflex mnemonic
Levels of jerks

Reticular formation

The reticular formation (formatio reticular) is a net-like mixture of grey and white matter and it is located in  the midbrain, pons, medulla oblongata and spinal cord. Neurons which form this structure have dendrites with few branches and axons of ascending and descending direction. Besides axons have a lot of small branches and they are able to contact with many neurons and conduct impulses to many brain areas.

It was discovered that reticular formation has connections with limbic lobe, autonomic nervous system and hypothalamus.

The RF can be divided into four longitudinal zones (systematic approach). Functionally, the periaqueductal gray is also part of the RF.

  • Spinal cord – intermediate grey substance (central part)
  • Brainstem – nuclei of reticular formation  are divided into the central, medial and lateral ones.
    • Median: raphé nuclei, afferents fibres: FR, hypothalamus, limbic system, prefrontal cortex
    • Medial: nucleus reticularis gigantocellularis, nucleus reticularis pontis, heterogeneous; part of the ascending arousal system
    • Intermediate: locus coeruleus, nucleus ambiguous; afferents fibres: hypothalamus, limbic system, nucleus solitarius, cortex
    • Lateral: nucleus parabrachiales, nucleus tegmenti pedunculopontinus; afferents fibers: limbic system, amygdala, hypothalamus, cortex

Besides there are median nuclei, raphe nuclei of medulla oblongata and pons and central grey substance.

Central reticular nuclei – the most important ones are called tegmental nuclei.

Medial and lateral reticular nuclei – they are located around central group.    
Pons doesn’t contain lateral group.

The most important nuclei of reticular formation are:

  • Gigantocellular nucleus
  • Lateral reticular nucleus (medulla oblongata)
  • Raphe nuclei (medulla oblongata/ pons)
  • Nuclei of locus caeruleus (pons)
  • Interstitial nucleus
  • Pedunculopontine tegmental nucleus (midbrain)
  • Reticular nucleus of thalamus

Proper tracts of reticular formation connect nuclei of this formation. They pass in proper fasciculi of spinal cord. Example of cerebral proper tract is central tegmental tract. Proper pathways are very expanded and join all parts of reticular formation.

Ascending tracts connect reticular formation with all parts of CNS. There are i.e. spinoreticular tract, cerebelloreticular tracts, tectoreticular tracts, corticoreticular tracts and much more.

Descending tracts pass back to many parts of CNS. There are i.e. reticulospinal tracts, reticulothalamic tracts and reticulocerebellar tracts.

The reticular formation is responsible for conscious watch and responding to external stimuli. It participates in mechanisms which determine cycle sleep–waking. Pathways which pass through parts of reticular formation influence action of important life centres which deals with heart work, breathing, arterial pressure. It is known that neurons of reticular formation secrete neurotransmitters which it is believed participate in concrete functions.  

  • It acts as an unspecific mediator between sensory systems and the cortex and controls vital vegetative functions such as respiratory and cardiovascular functions and sleep/waking cycles.
  • control of muscle tone and myotatic reflexes
  • central transmission of sensory impulses
  • cardiovascular functions – solitary tract nucleus sends efferent to RF and recives fibers from baroreceptors in carotid sinus and aortic arch
  • ARAS = Ascending Reticular Activation System – lesion of RF in brainstem may produce coma
  • sleep (nonREM, REM)

Nuclei of the Cranial Nerves

There are the following kinds of fibres inclosing in cranial nerves:

  •  Motor fibres
  • Sensory fibres
  • Parasympathic fibres

These fibres  begin or end in nuclei which are located at the brainstem. There are two groups of motor nuclei, parasympathetic nuclei, and nuclei of sensory functions.

  • Nucleus of abducent nerve (nucleus nervi abducentis) – on the level of the facial colliculus- pons
  • Nucleus of hypoglossal nerve (nucleus hypoglosalis) medulla oblongata
  • Nucleus of trochlear nerve (nucleus nervi trochlearis) tegmentum – midbrain
  • Nucleus of oculomotor nerve (nucleus nervi oculomotorii) tegmentum – midbrain
  • Nucleus ambiguus (nucleus ambiguus) – in the medulla oblongata
  • Facial motor nucleus (nucleus nervi facialis) – in the pons
  • Trigeminal motor nucleus (nucleus motorius nervi trigemini) – in the pons.
  • Nucleus of accessory nerve (nucleus nervi accessorii) – cervical part of spinal cord
  • Superior salivatory nucleus (nucleus salivarius superior) – in the pons for CN VII.
  • Inferior salivatory nucleus (nucleus salivarius inferior) – in the medulla oblongata for CN IX.
  • Dorsal motor nucleus of vagus (nucleus dorsalis nervi vagi) – medulla oblongata.
  • Accessory nucleus of oculomotor nerve (nucleus accessories nervi oculomotorii)  – midbrain.
  • Nuclei of trigeminal nerve – medulla oblongata, pons and midbrain
  • Nuclei of spinal tract (CN V)

Cochlear nuclei (interior and posterior) – pons

Vestibular nuclei ( rostral, caudal, lateral and medial ) pons and medulla oblongata

Nucleus of the solitary tract /for CN VII, IX, X/ (nucleus solitarius) – medulla oblongata

Afferent Pathways of Special Senses

There are five afferent pathways of SPECIAL SENSATION:

  1. Olfaction (smell, SVA): olfactory pathway
  2. Vision (SSA): visual pathway
  3. Gustatory Sensation (taste, SVA): taste pathway
  4. Auditory Sensation (Hearing, SSA): auditory pathway
  5. Vestibular sensation (equilibrium, SSA): vestibular pathway

Visual pathway – visual impulses from the retina pass to:

  1. Ganglion cells  layer –  the  1st neuron – branches pass to:
  2. Optic nerve; to the optic  chiasm,  where  they undergo partial deccusation and enter the optic tract; each  tract  contain ipsilateral temporal fibres and contralateral nasal fibres; the fibres of  the  optic tracts terminate in:
  3. The lateral geniculate nucleus – the 2nd neuron – fibres arrising in the lateral geniculate  body  form  the optic radiation which passes  through  the  posterior  limb  of  the  internal capsule, then the lateral to the posterior horn of the lateral ventricle and reaches the calcarine sulcus on the medial surface  of  the  occipital  lobe (visual cortex). Some fibres, however,  pass  beyond  the  thalamus  to  the superior colliculus (visual reflex pathways).
The neurons of the visual pathway.

Olfactory Pathway (olfactory impulses): 

  1. from sensory mucosa in the upper part  of each nasal cavity
  2. pass from mitral cells – 1st neuron – along the olfactory nerves to
  3. the olfactory bulb – 2nd neuron – their branches pass olfactory tract  and olfactory trigone to:
  4. the piriform area (prepiriform  cortex, paraamygdaloid cortex & endorhinal cortex) – the 3rd neuron

Taste impulses carried in the CN VII, IX, X pass to:

  1. Nucleus tractus solitarius; pass  via thalamus to the  insular cortex  (probably).

Auditory impulses from the spinal organ to:

  1. the bipolar cells – the 1st neuron– to:
  2. The dorsal & ventral cochlear nuclei – the 2nd neuron – fibres cross the midline mostly as a ventrally placed decussating bundle of  the  trapezoid body. Some fibres cross the brain stem  dorsal  to  the trapezoid  body and synapse in the contralateral trapezoid nucleus. The axons from these  nuclear groups form the lateral lemniscus which ascends.
  3. To the medial geniculate body – the 3rd neuron – fibres from neurones of the medial geniculate body pass in the posterior limb of the internal capsule to the superior temporal gyrus.

Vestibular impulses arising in specialised organs of balance pass to:

  • bipolar cells – the  1st  neuron  – and vestibular nerve  to the dorsal vestibular nuclei – the 2nd  neuron – fibres  to  the inferior  cerebellar peduncle to the flocculonodular lobe of the cerebellum –  the  3rd  neuron.
  • Others fibres probably lead  to  the  thalamus  and  thence  to  the  cortex /superior temporal gyrus.