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.
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”.
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 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.
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.
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.
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.
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
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.
Gross subdivisions of the Nervous System
The Central Nervous System (CNS) consists of two parts:
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:
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.
Developmental relations of the CNS.
The brainstem consists of three following structures:
- Medulla oblongata
- Pons
- Mesencephalon
Phylogeny the cerebral cortex divides into:
Anatomical, clinical & functional division of the nervous system
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 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
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 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
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.
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.
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)
Frontal lobe (lobus frontalis) is the largest of all the lobes. It consists of:
Parietal lobe (lobus parietalis) consists of:
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)
Temporal lobe (lobus temporalis) consists of:
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)
Organization of the cerebral cortex
- Molecular layer or plexiform layer (lamina molecularis)
- External granular layer (lamina granularis externa)
- External pyramidal layer (lamina pyramidalis externa)
- Internal granular layer (lamina granularis interna)
- Internal pyramidal layer (lamina pyramidalis interna)
- Multiform layer (lamina multiformis)
- Stria of molecular layer or stria of plexiform layer (stria laminae molecularis)
- Stria of external granular layer (stria laminae granularis externae)
- Occipital stripe or occipital line (stria occipitalis)
- Stria of internal granular layer (stria laminae granularis internae)
- Stria of internal pyramidal layer (stria laminae pyramidalis internae)
- 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.
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
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.
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
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
The projection fibres originate from pyramidal neuron cell bodies in lamina 5.
The commisures of telencephalon are formed by the:
nervous system.
On the transverse section of the forebrain the fibres pass as:
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:
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.
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 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.
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.
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.
Diencephalon (interbrain)
Thalamencephalon
The thalamus is an egg-shaped mass of grey matter, arranged into nuclei, and divided by two bands of white matter:
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.
The thalamus has four surfaces:
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:
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).
The metathalamus formed posterior part of halamencephalon situated below the pulvinar.
It has the geniculate bodies:
The epithalamus is on the most dorsal part of thalamencephalon. It consists of several anatomical structures:
Hypothalamus
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 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 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:
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.
Brainstem
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
The tectal plate has following parts:
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 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.
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.
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.
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:
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).
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
The Internal Carotid Artery (ICA) (arteria carotis interna) – supplies the greater part of the brain and the contents of the orbit.
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.
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.
Metencephalon
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:
- Superior medullary velum (velum medullare superius) thin sheet of white matter, pia and ependyma.
- Superior cerebellar peduncule (pedunculus cerebellaris superior) joins the cerebellum with the midbrain (red nucleus).
- 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:
Pons has two surfaces:
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 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.
- Vermis (vermis ) – central part of the cerebellum, it includes:
Surface of cerebellar cortex forms cerebellar fissures and folia 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:
- Anterior lobe of cerebellum (lobus cerebelli anterior) extends from the superior medullary velum to the primary fissure
- Posterior lobe of cerebellum (lobus cerebelli posterior) lobe extends from the primary fissure to the posterolateral fissure
- Flocculonodular lobe (lobus flocculonodularis) = nodule + flocculus
Usually the cerebellum is divided into following lobules:
Subdivision of cerebellum (lobules, top to bottom)
| Vermis | Hemispheres of cerebellum |
| Superior surface | |
| Lingula | Vinculum |
| Central lobule | Wing of central lobule |
| Culmen | Quadrangular lobule |
| Primary fissure | |
| Declive | Simple lobule |
| Folium of vermis | Superior semilunar lobule |
| Horizontal fissure | |
| Inferior surface | |
| tuber of vermis | inferior semilunar lobule |
| pyramid of vermis | biventer lobule |
| uvula of vermis | tonsil of cerebellum |
| Posterolateral fissure | |
| Nodule | Flocculus |
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
- Cerebellar cortex
- 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.
Superior cerebellar peduncle:
- Cerebellothalamic fiber: from dentate nucleus, emboliform nucleus and globose nucleus to VPLo, VLc, CL
- Cerebellorubral fibers: to red nucleus in mesencephalon from nucleus interpositus and dentate nucleus ascending portion of Uncinate fasciculus of Russell – dentatorubrothalamic tract (brachium conjunctivum)
- Superior cerebelloreticular tract: to reticular formation in mesencephalon, pons and medulla oblongata
Inferior cerebellar peduncle:
- 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.
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:
- Clarke’s nucleus for the lower limb (dorsal spinocerebellar tract).
- Accessory cuneate nucleus for the upper limb (cuneocerebellar tract).
It has reciprocal (mutual or joint) connections with:
- reticular formation to control axial musculature.
- contralateral primary motor cortex (areas controlling axial musculature) to control on-going motor activities.
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.
- 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).
- Coordination of half-automatic movement of walking and posture maintenance – posture, gaits (asynergy – loss of coordination).
- Adjustment of muscle tone
- Motor leaning – motor skills
- 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:
- Anterior median fissure (fissura mediana anterior) iscontinuous with the spinal cord. Anterior median fissures of the medulla oblongata and spinal cord are separated by:
- The pyramidal decussation (decussatio pyramidum) – the crossing of the majority of the corticospinal tracts.
- Pyramid (pyramis) which is the elevation of the pyramidal tract with laterally located anterior lateral sulcus (sulcus anterolateralis) for exit of CN XII.
- 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.
There are two parts on the horizontal cross-section:
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:
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)
- Medial eminence but it is divided by the striae medullaris into:
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:
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:
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)
- 1st and 2nd ventricle (lateral ventricle)
- Interventricular foramina
- 3rd ventricle
- Cerebral aquaeduct
- 4th ventricle
- Lateral aperture and median aperture of 4th ventricle
- Subarachnoid space
- Arachnoid villi
- 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:
- Median eminence is a small swelling shows by tuber cinereum immediately behind the infundibulum
- Neurohypophysis
- Vascular organ of the lamina terminalis
- Subfornical organ
- Subcommisural organ
- 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.
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.
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:
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).
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 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:
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 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).
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.
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 lesion of the nigrostriatal tract and the degeneration of dopamine neurons primarily in substantia nigra increases level of dopamine and gives Parkinson’s disease.
Amygdaloid body
Rhinencephalon
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:
The limbic lobe (lobus limbicus) is located around diencephalons. It has two portions:
Externals portion contains:
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.
Diencephalic Areas of Limbic System are formed by:
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 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.
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.
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.
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 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):
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):
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
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 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.
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:
Origin: Cerebral Cortex, the pyramidal cells (mostly), fibers arise from the UMN, the 1st neuron pass through:
- Corona radiata
- Posterior limb of internal capsule
- Crus cerebri (middle portion)
- Longitudinal pontine fiber
- Pyramidal decussation of pyramid (the most of the fibers decussate just below the junction the medulla)
- Lateral corticospinal tract
- Pyramid
- Anterior corticospinal tract
Termination: grey matter of spinal cord – anterior horn (spinal laminae VII -IX).
The corticobulbar fibers projecting to cranial motor nuclei in the lower brainstem:
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.
Mnemonic
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)
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:
from:
- 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)
via:
- Subcortical nuclei (which are found the basal nuclei)
- Striatum (centre of muscle tone and automatic movments)
- Subthalamus of the forebrain – subthalamic 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
to:
- Lower motor neurons.
Upper motor neurons (UMNs) are located in the cortex:
- Primary Motor Area
- Premotor Area
- Paracentral Lobule
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:
There are present some more pathways in spinal cord which belong to pyramidal and extrapyramidal tracts.
Pathways of the spinal cord – setting:
- 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.
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.
- 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:
- Branches of the 1st neuron may ascend in the posterior column of the spinal cord to:
- The lateral cuneate nucleus of the medulla – the 2nd neuron
- 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
- Impulses run from receptor cells.
- In spinal nerve the first neuron of cell bodies in the dorsal root ganglion to:
- 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:
- The thalamus – specifically the ventral nucleus – the 3rd neuron.
- The axons of the ventral nuclei ascend through the internal capsule to the postcentral gyrus.
- Impulses run from receptor cells.
- 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.
- 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:
- The thalamus – venteroposterior nucleus – the 3rd neurons.
- The axons of the ventral nuclei ascend through the internal capsule.
- Termination: postcentral gyrus
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.
Mnemonic
Reticular formation
Nuclei of the Cranial Nerves
Afferent Pathways of Special Senses
There are five afferent pathways of SPECIAL SENSATION:
- Olfaction (smell, SVA): olfactory pathway
- Vision (SSA): visual pathway
- Gustatory Sensation (taste, SVA): taste pathway
- Auditory Sensation (Hearing, SSA): auditory pathway
- Vestibular sensation (equilibrium, SSA): vestibular pathway
Visual pathway – visual impulses from the retina pass to:
- Ganglion cells layer – the 1st neuron – branches pass to:
- 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:
- 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).
Olfactory Pathway (olfactory impulses):
- from sensory mucosa in the upper part of each nasal cavity
- pass from mitral cells – 1st neuron – along the olfactory nerves to
- the olfactory bulb – 2nd neuron – their branches pass olfactory tract and olfactory trigone to:
- the piriform area (prepiriform cortex, paraamygdaloid cortex & endorhinal cortex) – the 3rd neuron
Taste impulses carried in the CN VII, IX, X pass to:
- Nucleus tractus solitarius; pass via thalamus to the insular cortex (probably).