CNS PART 2

Question 1

• Diencephalon - structure, subdivision and functional organization*
• Thalamus - nuclei, afferent and efferent connections of main nuclei, their function 391*

Hypothalamus - subdivisions, connections and function 402

Anatomical background of hypothalamohypophyseal regulation

Basal ganglia, their connections and function, parkinsonism 334

• Main functional areas of cerebral cortex*
• White matter of hemispheres - association and commissural fibers, internal capsule (draw scheme of tracts in internal capsule)*

Ventricular system of brain (draw scheme), circulation of liquor, hydrocephalus

Brain vessels and blood-brain barrier, brain dysfunctions related to inadequate blood supply via particular blood vessels brain damage due to vascular occlusion

Corticospinal (pyramidal) and corticonuclear tract

Auditory pathway

Visual pathway and visual cortical areas

Olfactory and gustatory pathway, olfactory nerve

Limbic system - connections and function (cortical areas, hippocampal formation, amygdalar complex)

Neurotransmitters in the CNS, main brain chemical systems

Answer 1

list

Question 2

Diencephalon - structure, subdivision and functional organization

Answer 2

Subdivisions of the Cerebrum

• Largest part of the brain
• In anterior and middle cranial fossae of the skull
• Occupying the whole concavity of the vault of the skull.
• Two parts:
  
  • Diencephalon, which forms the central core,
  • Telencephalon, which forms the cerebral hemispheres.

General: diencephalon

• Midline structure with symmetrical right and left halves.

1- Inferior surface/floor

• Only area exposed to the surface
• From anterior to posterior:
  
  • Optic chiasma, with the optic tract on either side
  • Infundibulum, with the tuber cinereum
  • Mammillary bodies

2- Superior surface/roof

• Concealed by the fornix
• Formed by the thin tela choroidea,
  • Combination of two membranes:
    
    • the ependyma and pia mater.
• Within the tela choroidea are two plexuses of blood vessels (one on either side of the middle line) that bulge downwards into the cavity of the third ventricle.
  
  • These are the choroid plexuses of the third ventricle which functions as a point of production of the cerebrospinal fluid (CSF).

3- Lateral surface

• Bounded by the internal capsule of white matter

4- Medial surface

• i.e., the lateral wall of the third ventricle
• Superior part: by the medial surface of the thalamus
• Inferior part: hypothalamus
• These two areas are separated from one another by hypothalamic sulcus.
• Stria medullaris thalami
  
  • Forms a ridge along the superior margin of the medial surface
  • A bundle of nerve fibers, which are afferent fibers to the habenular nucleus

Divided into four major parts:

(1) thalamus
(2) subthalamus
(3) epithalamus
(4) the hypothalamus
(1) Thalamus
* Interconnection of AF PT to cortex
(2) Subthalamus
* Between the thalamus and the tegmentum of the midbrain

• Motor and emotional neural patterns?
  
  • important connections with the corpus striatum

(3) Hypothalamus

• Control center for autonomic and endocrine
  
  • Mamillary bodies
  • Tuber cinerum
  • Infindibulum

(4) Epithalamus/hypophysis
* Habenular nuclei and their connections and the pineal gland
(5) Metathalmus
* Containg ncl of visual and auditory tract

(~) Optic thalamus

Development:

• Once the neural tube has closed, the three primary vesicles complete their development
  
  • The forebrain vesicle (prosencephalon)
  • The midbrain vesicle (mesencephalon)
  • Hindbrain vesicle (rhombencephalon)
• By the fifth week, the forebrain (and hindbrain) divide into two secondary vesicles
  • Telencephalon, with its primitive cerebral hemispheres
    
    • Cerebral hemisphere, basal ganglia,

hippocampus

* **_Diencephalon_**, develops **optic vesicles** (optic vesicle and stalk ultimately will form the retina and optic nerve.)
    * **Thalamus, hypothalamus, pineal body,**

infundibulum

• From diencephalic vesicle, continuation of the plates of the neural tube
  
  • Canalis centralis → 3rd ventricle
  • Alar plate→ thalamus (sensory structure), and subthalamus
    
    • above hypothalamic sulcus
  • Basal plate→ hypothalamus (motoe structure)
    
    • below
    • viseral motor acitivity
    • (control of somatic motor activity: from HYPO-T: internal capsule: BG: Midbrain)

Blood supply

• The diencephalon is richly supplied by several blood vessels:
• Posterior cerebral artery
  
  • ​thalamogeniculate branches
  • thalamoperforating branches
• Posterior communicating artery.
  
  • ​thalamoperforating branches

Epithalamus

• Habenular nuclei and their connections and the pineal gland.
• Habenular Nucleus
  
  • Small group of neurons
  • Medial to the posterior surface of the thalamus.
  • Believed to be a center for integration of olfactory, visceral, and somatic afferent pathways.
  • Afferent fibers:
    
    • Amygdaloid nucleus through the stria medullaris thalami;
    • Hippocampal formation through the fornix.
    • Some of the fibers of the stria medullaris thalami cross the midline and reach the habenular nucleus of the opposite side; these latter fibers form the habenular commissure
  • EF:
    
    • Interpeduncular nucleus in the roof of the interpeduncular fossa,
    • Tectum
    • Thalamus
    • Reticular formation of the midbrain.

Ephysisis

• Behind upper posterior end of 3rd ventricle
• Part of epithalamus
• Rudimentary endocrine gland with supressive efect on sexual glands pubertas praecox
• Dorsally extends above brain stem (above lamina quadrigemina of mid brain)
• melatonin  change of level during day
• acervulus cerebri (= calcium concrements in adults) – CT, MRI

Pineal Gland (Body)

• Small structure
• Attached by the pineal stalk to the diencephalon.
• It projects backward so that it lies posterior to the midbrain
  
  • The superior part of the base of the stalk contains the habenular commissure;
  • The inferior part of the base of the stalk contains the posterior commissure.
• Two types of cells are found in the gland, the
  
  • Pinealocytes
  • Glial cells.
• Functions of the Pineal Gland
  
  • important endocrine gland influencing
    
    • activities of the pituitary gland,
    • the islets of Langerhans of the pancreas,
    • the parathyroids,
    • the adrenal cortex and the
    • adrenal medulla,
    • the gonads.
  • Their actions are mainly inhibitory ( directly/ indirectly) inhibit the secretion of releasing factors by the hypothalamus.
    
    • It is interesting to note that the pineal gland does not possess a blood-brain barrier.

Subthalamus

• Positioned below thalamus – separated by Forels field H1
• Externally to hypothalamus – w/o visible border
• Zona incerta
  
  • The incerta zone is a strip of gray matter below the thalamus
  • Composition resembles RF
  • Integration of inputs from cortex and stem
  • GABA inhibits ncll. intralaminares and association nuclei of thalamus (similarly to ncll. reticulares thalami)
• Nucleus subthalamicus (= corpus Luysi)
  
  • Connected to basal ganglia system (Glu into globus pallidus) excitatory effect
  • Lesion: hemibalismus (rough non coordinated movements of contralateral cingulum muscles) after CMP, non ketonic hyperglycemia
• Forels fields = campi perizonales = H zone (Haubenfelder)
• CONNECTIONS??????

Question 3

Thalamus - nuclei, afferent and efferent connections of main nuclei, their function

→

391

Answer 3

General

• “Secretary of brain” all except for smell
• Consists of several nuclei that are connected to the cerebral cortex and functions as the main conductor of sensory information
  
  • Nuclei parcellated according to position orconnection

Topography

• Laterally: internal capsule
• Ventrally: subthalamus/ hypothalamus
• Basally: midbrain
• Medialy: third ventricle
• The posterior end is expanded to form the pulvinar, which overhangs the superior colliculus

External features: ?

• stria medularis thalami:
• taenia choroidea:
• Choroideus plexsus
• Lamina affixa thalami
• stria terminalis: containing fobers from amygdeloid body to hypothalmus
• taenia thalami: attachment of the 3 ventrical roof

General Appearances of the Thalamus

• Large, egg-shaped mass of gray matter that forms the major part of the diencephalon.
• There are two thalami, one in each side of the third ventricle
• The anterior end
  
  • Narrow and rounded and forms the posterior boundary of the interventricular foramen.
• The posterior end:
  
  • Is expanded to form the pulvinar, which overhangs the superior colliculus
• The inferior surface
  
  • Continuous with the tegmentum of the midbrain.
• The medial surface
  
  • Forms part of the lateral wall of the 3 ventricle and
  • Connected to the opposite thalamus by a band of gray matter the interthalamic connection (interthalamic adhesion).

Subdivisions of the Thalamus

• Covered on its superior surface by a thin layer of white matter, called the stratum zonale
• Lateral surface by another layer, the external medullary lamina
• Internal medullary lamina:
  
  • Vertical sheet of white matter which divides the gray matter of the thalamus into medial and lateral halves
  • Anterosuperiorly, the internal medullary lamina splits, resembling a Y shape.
• The thalamus thus is subdivided into three main parts;
  
  • Anterior part: lies between the limbs of the Y,
  • Medial parts: sides of the stem of the Y
  • Lateral parts: sides of the stem of the Y
• Each of the three parts of the thalamus contains a group of thalamic nuclei

Ventral group - anterior, lateral, posterior medial, posterior lateral nuclei

Medial group - median, medial dorsal, medial nuclei

Geniculate bodies - medial, lateral nuclei

Anterior and reticular nuclei

Anterior part:

• AF:
  
  • Mammillothalamic tract from the mammillary nuclei.
  • Reciprocal connections with the cingulate gyrus and hypothalamus.
• Function: specific non sensory
  
  • Closely associated with that of the limbic system
  • Concerned with emotional tone and the mechanisms of recent memory.

Medial Part

• Large dorsomedial nucleus
• Several smaller nuclei
• The dorsomedial nucleus has
  
  • two-way connections with the whole prefrontal cortex of the frontal lobe of the cerebral hemisphere.
  • It also has similar connections with the hypothalamic nuclei.
  • It is interconnected with all other groups of thalamic nuclei. The medial part of the thalamus is responsible for the integration of a large variety of sensory information, including somatic, visceral, and olfactory information, and the relation of this information to one’s emotional feelings and subjective states.

Olfactory and limbic brainncl. MD (mediodors.) prefrontal cortex (thinking, reasoning, mood, mind state – integration with sensory inputs)

Nuclei:

• Non specific NCL:
  
  • To areas of cortex and BG, part of activating system. transmits impulses mainly from RF
    
    • Intralaminar
    • Mediani
• Specific Sensory:
  
  • sensory pathways, transmits to enclosed careas of cortex
    
    • Ventral posterior medialis
    • Ventral posterior lateralis
    • Medial Geniculate body
    • Lateral geniculate body
• Specific non sensory:
  
  • Transmits to enclosed careas of cortex
  • Ventral lateral ncl.
  • Ventral anterior ncl.
    
    • AF →Basal GGL
    • EF →premotor and motor cortex
  • Anterior and medial ncll.
    
    • AF →amygdala, hippocampus, hypothalamus
    • EF → limbic system
• Assosiation:
  
  • recieve impulses from relay NCL anf pass to various careas of cortex, coordinators og thalamic NCL- integrating impulses
    
    • Lateralis
    • posteriores

Question 4

Basal ganglia, their connections and function, parkinsonism

334

Answer 4

General:

• Apart of the gray matter of the terminal brain outside the thalamus .
• Developmentally old structures.
• Used in the creation and control of movement, they also participate in the cognitive functions and functions of the limbic system

Morphology

• Caudate nucleus
• Putamen
• Globus pallidus - we divide it into:
  
  • globus pallidus medialis (pallidum internum) - output basal ganglion;
  • globus pallidus lateralis (pallidum externum) - intrinsic basal ganglion.
• Nucleus caudatus + Putamen= Corpus striatum, neostriatum
• Putamen + Globus pallidus=Nucleus lentiformis
• Developmentally, the basal ganglia also include the corpus amygdaloideum but it is functionally classified as a limbic system

Caudate ncl:

• Head, body, tail- terminates at amygdaloid body
• AF: association cortex, caput mostly from prefrontal cortex (cognitive function) putamen (shell)
• Function:
  
  • Controls speed and accuracy of directed movments
  • Involved in executive function
    
    • decision making processes related to focus and attention
  • Reward and reinforcement
  • Assosiative learning
  • Emotions: attraction
  • Procedural learning: tie shoes
  • Inhibition of action based on pervious experience

Putamen

• Connected with ncl. caudatus via
  
  • striae(verticallyviacapsulainterna)
  • ncl.accumbens(septi)(ventrobazally)????
• Seperated from
  
  • Globus pallicidus medially by external meduallry lamina
  • Caulstrum by external capsule
  • Thalamus by internal capsule
• ​AF: motor cortex
• Function:
  
  • Regulation of movments
  • Stores information about learnt movments

– Irritation leads to hedony (similar to heroin users) = plenty of dopamin from area ventralis Tsai

Globus Pallicidus

• Paleostriatum
• Functions as EF portion

Additional:

• Substantia innominata Reicherti -
  
  • A group of structures basally from the basal ganglia consisting of
    
    • Nucleus accumbens, Striatum ventrale
      
      • the ventral part of the striatum
      • pleasure center
      • reward and reinforcement
      • linked to impulse control dissorders
    • Pallidum ventrale
      
      • the ventral parts of the globus pallidus ;
    • Rostral (medial and central) nuclei of the corpus amygdaloideum
    • Nucleus basalis Meynerti -
      
      • a dispersed gray matter formed by acetylcholine-producing neurons;
• Nucleus subthalamicus (corpus Luysi) -
  
  • Part of diencephalon
  • Basally from the zona incerta
  • numerous connections to GP
  • Connected as a so-called intrinsic (intervening) nucleus into the basal ganglia circuit;
  • Function: suppersion of unwated movments
• Substantia nigra
  
  • In midbrain, inferior to corpus striatum- many connections
  • Dark nucleus
  • Function: send signals to BG to increase/decrease movment, modulatory structure
  • We distinguish:
    
    • Pars compacta -
      
      • monoaminergic nucleus producing dopamine for the corpus striatum (A9 in the system of monoaminergic nuclei);
    • Pars reticularis - output basal ganglion.

BG connectionsL

The general scheme is:

Cortex → input basal ganglion → exit basal ganglion → thalamus → cortex

• Input basal ganglia
  
  • Receive information from the cerebral cortex;
  • their neurons are inhibitory (mediator of GABA );
  • corpus striatum (ncl. caudatus, putamen, striatum ventrale = ncl. accumbens septi);
• Output BG
  
  • Send information through the thalamus to the cerebral cortex or directly to the brainstem ( reticular formation)
  • Neurons are also inhibitory (GABA);
  • globus pallidus medialis, pallidum ventrale (→ cortex)
  • substantia nigra, pars reticularis (→ strain?);
• Intrinsic basal ganglia:
  
  • Transfer information between input and output cores in indirect pathways
  • Globus pallidus lateralis (inhibitory neurons - GABA);
  • Ncl. subthalamicus (excitatory neurons - glutamate );
  • they modulate the activity of the corpus striatum and direct / indirect pathways via dopamine - pars compacta substantiae nigrae.?
    
    • pars compacta substantiae nigrae
    • • area tegmentalis ventralis (ncl. subbrachialis)

Direct circuit

• Disinhibition of the thalamus, which is equivalent to the excitation of the motor cortex
• Cortex
  
  • Excites (Glu)→
• Striatum (caudate nucleus and putamen).
  
  • inhibitory neurons (GABA)
• 1- Internal globus pallidus.
  
  • inhibitory neurons (GABA)​
• 2- Substantia nigra, Pars reticularis
  
  • ​disinhibition of the thalamus
• Thalamus
  
  • Excitatory
• Cortex
  
  • (prefrontal, premotor and supplementary cortex)
  • Affect the planning of the movement by synapsing with the neurons of the corticospinal and corticobulbar tracts.

Indirect circuit

• Cortex
  
  • Excites (Glu)→
• Striatum (caudate nucleus and putamen).
  
  • inhibitory neurons (GABA)
• External globus pallidus.
  
  • ​disinhibition of the subthalamic ncl
  • default setting is to send inhibition signals, but when its itself is inhibited then it “activates subthalamus”
• _​_Subthalamic ncl
  
  • ​Excitatory
• Internal globus pallidus
  
  • ​increase inhibitory neurons (GABA)
• Thalamus
  
  • inhibitory
• Cortex

So functionally the striatum inhibits the external globus pallidus, and that causes a disinhibition of the subthalamus. For that reason, the neurons of the subthalamus become more active, and they excite the internal segment of the globus pallidus. So finally this loop inhibits the thalamic nuclei. The final result of this pathways is a decreased activity of the cortical motor neurons, and consequential suppression of the extemporaneous movement.

Cortex →

• primary motor (4),
• premotor and supplementary motor (6),
• somatosensitive (3, 1, 2)

→Input BG → (inhibitory, GABA)

• Striatum: putamen

→Output BG → (inhibitory, GABA)

• Globus pallidus medialis,
• Substantia nigra - pars ret.
• *disinhibition of the thalamus: when striatum inhibits output BG, it cancels the inhibitory affect of them on thalamus, allowing it to relase stimulatory impulses to cortex

→Thalamus →

• ncl. anterior ventrales (VA)
• ncl. lateral ventrales (VL)

→Cortex/

• primary motor (4),
• premotor and supplementary motor (6),

Function→???

• Processing inctruction for exicution of movment of extremities and trunk
• Execution:
  
  • Cortico spinal tr.
  • Reticulo spinal tr.

Indirect circuit:

→Cortex →

• primary motor (4),
• premotor and supplementary motor (6),
• somatosensitive (3, 1, 2)

→Input BG →

• Globus pallidus lateralis→
• Subthalamic ncl

→Output BG →

→Thalamus →

→Cortex/Function→

→Cortex →

→Input BG →

→Output BG →

→Thalamus →

→Cortex/Function→

Question 5

Main functional areas of cerebral cortex

308

Answer 5

• Folds/gyri which are separated from each other by sulci or fissures increase the surface area of the cerebral cortex maximally
• Division into lobes
  
  • frontal, parietal, temporal, and occipital lobes
  • The central and parieto-occipital sulci and the lateral and calcarine sulci are boundaries used for the division of the cerebral hemisphere into lobes

Main Sulci

• The central sulcus
  
  • anterior:
  • posterior: general sensory cortex
  • It runs downward and forward across the lateral aspect of the hemisphere
  • • The lateral sulcus
  • Mainly on the inferior and lateral surfaces of the cerebral hemisphere.
  • An area of cortex called the insula lies at the bottom of the deep lateral sulcus and cannot be seen from the surface unless the lips of the sulcus are separated

The cerebral cortex is organized into vertical units or columns of functional activity

A functional unit extends through all six layers

Each unit possesses afferent fibers, internuncial neurons, and efferent fibers.

. The horizontal cells of Cajal permit activation of vertical units that lie some distance away from the incoming afferent fiber

Frontal Lobe

Histologically: almost complete absence of the granular layers and the prominence of the pyramidal nerve cells.

The giant pyramidal cells of Betz, which can measure as much as 120 μm long and 60 μm wide, are concentrated

most highly in the superior part of the precentral gyrus and the paracentral lobule; their numbers diminish as one passes anteriorly in the precentral gyrus or inferiorly toward the lateral fissure.

Primary motor cortex

• (Brodmann area 4)
• Precentral gyrus on the frontal lobe
• Primary motor control of the corticospinal tract
  • carry out the individual movements of different parts of the body.
• Motor homunculus
  
  • Body parts of higher sensitivity or fine motor skills are represented in larger areas than others
  • Arranged medially to laterally as follows:
    
    • toes, ankle, knee, hip, trunk, shoulder, elbow, wrist, hand, little finger to thumb, eye, facial expression, mouth, chin, tongue, swallowing
    • Movements of the anal and vesical sphincters are also located in the paracentral lobule.
• Effect of lesion
  
  • Contralateral upper motor neuron dysfunction (e.g., contralateral movement paralysis)
  • Lesions in the paracentral lobule can cause urinary incontinence

Premotor cortex

• (Brodmann area 6)
• Anterior to the precentral gyrus on the frontal lobe
• Contributes to the corticospinal tract
  • Aids in control of axial and proximal muscles
  • Informs the primary motor cortex before execution of movements
  • Stronger stimulation is necessary to produce the same degree of movement as in M I
• Has no giant pyramidal cells of Betz.

Frontal eye field

• (Brodmann area 8)
• Posterior part of the middle frontal gyrus
• Controls voluntary saccadic eye movements
• Stimulation causes contralateral conjugate deviation of the eyes
• Effect of lesion
  
  • Transient ipsilateral conjugate deviation of the eyes

Prefrontal cortex

• (prefrontal association area)
• Connected to the mediodorsal nucleus of the thalamus
• Contain Brodmann areas 8–14, 24, 25, 32, and 45–47
• Concerned with the makeup of the individual’s personality, also exerts its influence in determining the initiative and judgment of an individual
• Lesions (e.g., frontotemporal dementia) cause
  
  • frontal lobe syndrome
  • Personality changes
  • Social and sexual disinhibition
  • Aggression

Broca area

• (Brodmann area 44 and 45)
• Speech area
• Connected to Wernicke areavia thearcuate fasciculus
• The Broca speech area brings about the formation of words by its connections with the adjacent primary motor areas; the muscles of the larynx, mouth, tongue, soft palate, and the respiratory muscles are appropriately stimulated.
• Lesions
  
  • Broca aphasia
  • Nonfluent, telegraphic, and grammatically incorrect speech
  • Intact comprehension of simple language

The great majority of the corticospinal and corticobulbar fibers originate from the small pyramidal cells in this area.

The precentral area may be divided into posterior and anterior regions.

The posterior region: motor area: primary motor area,

• Brodmann area 4, occupies the precentral gyrus extending over the superior border into the paracentral lobule

The anterior region: premotor area, secondary motor area,

• Brodmann area 6 and parts of areas 8, 44, and 45.
• It occupies the anterior part of the precentral gyrus and the posterior parts of the superior, middle, and inferior frontal gyri.

The primary motor area, if electrically stimulated, produces isolated movements on the opposite side of the body as well as contraction of muscle groups concerned with the performance of a specific movement. Although isolated ipsilateral movements do not occur, bilateral movements of the extraocular muscles, the muscles of the upper part of the face, the tongue, and the mandible, and the larynx and the pharynx do occur

Cells are present in the cerebral cortex:

(1) pyramidal cells

• 10 to 50 μm long
• giant pyramidal cells/Betz cells: cell bodies measure as much as 120 μm
• these are found in the motor precentral gyrus of the frontal lobe.
• Apices oriented toward the pial surface of the cortex.
  
  • From the apex of each cell, a thick apical dendrite extends upward toward the pia, giving off collateral branches.
• From the basal angles, several basal dendrites pass laterally into the surrounding neuropil.
  
  • Each dendrite possesses numerous dendritic spines for synaptic junctions with axons of other neurons
• The axon arises from the base of the cell body and either terminates in the deeper cortical layers or, more commonly, enters the white matter of the cerebral hemisphere as a projection, association, or commissural fiber.
  (2) stellate cells/ granule cells
• polygonal in shape, and their cell bodies measure about 8 μm in diameter
• Multiple branching dendrites and a relatively short axon, which terminates on a nearby neuron.
  (3) fusiform cells
• Long axis vertical to the surface and are concentrated mainly in the deepest cortical layers
• Dendrites arise from each pole of the cell body.
  • The inferior dendrite branches within the same cellular layer,
  • while the superficial dendrite ascends toward the surface of the cortex and branches in the superficial layers.
• The axon arises from the inferior part of the cell body and enters the white matter as a projection, association, or commissural fiber.
  (4) horizontal cells of Cajal
• small, fusiform, horizontally oriented cells found in the most superficial layers of the cortex
• dendrite emerges from each end of the cell, and an axon runs parallel to the surface of the cortex, making contact with the dendrites of pyramidal cells.

(5) cells of Martinotti

• Small, multipolar cells that are present throughout the levels of the cortex
• Short dendrites, but the axon is directed toward the pial surface of the cortex, where it ends in a more superficial layer, commonly the most superficial layer.
• The axon gives origin to a few short collateral branches en route.

Molecular layer (plexiform layer). This is the most superficial layer; it consists mainly of a dense network of tangentially oriented

nerve fibers (Figs. 8-1 and 8-3). These fibers are derived from the apical dendrites of the pyramidal cells and fusiform cells, the axons of

the stellate cells, and the cells of M artinotti. Afferent fibers originating in the thalamus and in association with commissural fibers also

are present. Scattered among these nerve fibers are occasional horizontal cells of Cajal. This most superficial layer of the cortex

clearly is where large numbers of synapses between different neurons occur.

2. External granular layer. This layer contains large numbers of small pyramidal cells and stellate cells (Figs. 8-1 and 8-3). The dendrites of

these cells terminate in the molecular layer, and the axons enter deeper layers, where they terminate or pass on to enter the white

matter of the cerebral hemisphere.

3. External pyramidal layer. This layer is composed of pyramidal cells, whose cell body size increases from the superficial to the deeper

borders of the layer (Figs. 8-1 and 8-3). The apical dendrites pass into the molecular layer, and the axons enter the white matter as

projection, association, or commissural fibers.

4. Internal granular layer. This layer is composed of closely packed stellate cells (Figs. 8-1 and 8-3). There is a high concentration of

horizontally arranged fibers known collectively as the external band of Baillarger.

5. Ganglionic layer (internal pyramidal layer). This layer contains very large and medium-size pyramidal cells (Figs. 8-1 and 8-3). Scattered

among the pyramidal cells are stellate cells and cells of M artinotti. In addition, there are a large number of horizontally arranged fibers

that form the inner band of Baillarger (Fig. 8-3). In the motor cortex of the precentral gyrus, the pyramidal cells of this layer are very

large and are known as Betz cells. These cells account for about 3% of the projection fibers of the corticospinal or pyramidal tract.

Figure 8-2 Neuronal connections of the cerebral cortex. Note the presence of the afferent and efferent fibers.

6. Multiform layer (layer of polymorphic cells). Although the majority of the cells are fusiform, many of the cells are modified pyramidal

cells, whose cell bodies are triangular or ovoid (Figs. 8-1 and 8-3). The cells of M artinotti also are conspicuous in this layer. M any nerve

fibers are present that are entering or are leaving the underlying white matter.

Variations in

Multiform layer (layer of polymorphic cells). Although the majority of the cells are fusiform, many of the cells are modified pyramidal

cells, whose cell bodies are triangular or ovoid (Figs. 8-1 and 8-3). The cells of M artinotti also are conspicuous in this layer. M any nerve

fibers are present that are entering or are leaving the underlying white matter.

Question 6

White matter of hemispheres - association and commissural fibers, internal capsule (draw scheme of tracts in internal capsule)

Answer 6

The white matter is composed of myelinated nerve fibers of different diameters supported by neuroglia.

Classiffication into three groups according to their connections:

(1) commissural fibers
(2) association fibers
(3) projection fibers

1- Commissure Fibers

• Connect corresponding regions of the two hemispheres.
• Corpus callosum
  
  • Bottom of the longitudinal fissure
  • Parts:
    
    • Rostrum: anterior
      • Continuous with the upper

end of the lamina terminalis

    * Genu
    * Body
    * Splenium
        * Thickened posterior portion
    * Traced laterally, the fibers of the **genu** curve forward into the **frontal lobes** and form the **forceps minor** and the fibers in the **splenium** arch backward into the **occipital lobe** and form the **forceps major**

• Anterior commissure: small bundle of nerve fibers that crosses the midline in the lamina terminalis
• Posterior commissure
  
  • Bundle of nerve fibers that crosses the midline immediately above the opening of the cerebral aqueduct into the third ventricle
  • Related to the inferior part of the stalk of the pineal gland.
• Fornix
  
  • Efferent system of the hippocampus that passes to the mammillary bodies of the hypothalamus.
  • The nerve fibers first form the alveus which is a thin layer of white matter covering the ventricular surface of the hippocampus, and then converge to form the fimbria.
  • The fimbriae of the two sides increase in thickness and, on reaching the posterior end of the hippocampus, arch forward above the thalamus and below the corpus callosum to form the posterior columns of the fornix.
  • The two columns then come together in the midline to form the body of the fornix
  • The function of the commissure of the fornix is to connect the hippocampal formations of the two sides.
• Habenular commissure
  
  • Crosses the midline in the superior part of the root of the pineal stalk
  • Associated with the habenular nuclei
  • Habenular ncl recieve afferents from the amygdaloid nuclei and the hippocampus.
    
    • These afferent fibers pass to the habenular nuclei in the stria medullaris thalami.
    • Some of the fibers cross the midline to reach the contralateral nucleus through the habenular commissure.

2- Association Fibers

• Connect various cortical regions within the same hemisphere
• Short and long groups
• The short association fibers
  
  • lie immediately beneath the cortex and connect adjacent gyri; these fibers run transversely to the long axis of the sulci
• The long association fibers
  
  • Collected into named bundles that can be dissected in a formalin-hardened brain.
  • Uncinate fasciculus
    
    • Connects the first motor speech area and the gyri on the inferior surface of the frontal lobe with the cortex of the pole of the temporal lobe.
  • Cingulum
    
    • is a long, curved fasciculus lying within the white matter of the cingulate gyrus
    • It connects the frontal and parietal lobes with parahippocampal and adjacent temporal cortical regions.
  • Superior longitudinal fasciculus
    
    • Largest bundle of nerve fibers.
    • Connects the anterior part of the frontal lobe to the occipital and temporal lobes.
  • Inferior longitudinal fasciculus
    
    • Runs anteriorly from the occipital lobe, passing lateral to the optic radiation, and is distributed to the temporal lobe.
  • Fronto-occipital fasciculus
    
    • Connects the frontal lobe to the occipital and temporal lobes.
    • It is situated deep within the cerebral hemisphere and is related to the lateral border of the caudate nucleus.

3- Projection Fibers

• Afferent and efferent nerve fibers passing to and from the brainstem to the entire cerebral cortex must travel between large nuclear masses of gray matter within the cerebral hemisphere.
• At the upper part of the brainstem, these fibers form a compact band known as the internal capsule:
  
  • which is flanked medially by the caudate nucleus and the thalamus
  • laterally by the lentiform nucleus
• Parts:
  
  • anterior limb
  • genu
  • posterior limb
• Once the nerve fibers have emerged superiorly from between the nuclear masses, they radiate in all directions to the cerebral cortex.
  
  • These radiating projection fibers are known as the corona radiata
  • The nerve fibers lying within the most posterior part of the posterior limb of the internal capsule radiate toward the calcarine sulcus and are known as the optic radiation

The internal capsule is frequently involved in vascular disorders of the brain.

• Common cause of arterial hemorrhage is atheromatous degeneration in an artery in a patient with high blood pressure.
• Because of the high concentration of important nerve fibers within the internal capsule, even a small hemorrhage can cause widespread effects on the contralateral side of the body. Not only is the immediate neural tissue destroyed by the blood, which later clots, but also neighboring nerve fibers may be compressed or be edematous.

description of the fornix is given on page 310.

Question 7

Ventricular system of brain (draw scheme), circulation of liquor, hydrocephalus

467

Answer 7

General:

• There are four ventricles that are interconnected to each other.
• The ventricles are developmentally derived from the cavity of the neural tube.
• The ventricles are lined throughout with ependyma (thin membrane of glial cells) and are filled with cerebrospinal fluid.
  
  • Cerebrospinal fluid (CSF), which serves as a fluid cushion and immunological reservoir

Lateral ventricles

• Paired (right and left)
• Located in the cerebral hemispheres
• C chape
  
  • Body: occupies the parietal lobe
    • Anterior horn: extend into the frontal lobes
    • Posterior horn: extend into the occipital lobes
    • Inferior horn: extend into the temporal lobe
• Drain into the 3rd ventricle via right and left interventricular foramina (of Monro)
• Body Topography:
  
  • Roof: corpus callosum
  • Floor: body caudate nucleus, lateral margin of the thalamus.
  • Medial wall:
    
    • is formed by the septum pellucidum anteriorly
    • The choroid plexus (irregular lateral edge of the tela choroidea) of the ventricle projects into the body of the ventricle through the slitlike gap known as choroidal fissure;
      
      • through it blood vessels of the plexus invaginate the pia mater of the tela choroidea and the ependyma of the lateral ventricle.

Third ventricle

• Single midline ventricle
  
  • ​Derived from the forebrain vesicle, is a slitlike cleft between the two thalami
• Located in the diencephalon
• Drains into the 4th ventricle via cerebral aqueduct (of Sylvius) (passes through the midbrain)
• The third ventricle has anterior, posterior, lateral, superior, and inferior walls and is lined with ependyma.
• Anterior wall:
  
  • Thin sheet of gray matter, the lamina terminalis, across which runs the anterior commissure
    
    • The anterior commissure is a round bundle of nerve fibers that are situated anterior to the anterior columns of the fornix; they connect the right and left temporal lobes.
• Posterior wall:
  
  • Formed by the opening into the cerebral aqueduct
  • Superior to this opening is the small posterior commissure.
    
    • Superior to the commissure is the pineal recess, which projects into the stalk of the pineal body. Superior to the pineal recess is the small habenular commissure.
• The lateral wall
  
  • Formed by the medial surface of the thalamus superiorly and the hypothalamus inferiorly
    
    • Separated by the hypothalamic sulcus.
    • The lateral wall is limited superiorly by the stria medullaris thalami.
  • The lateral walls are joined by the interthalamic connection.
• Superior wall/ Roof is
  
  • Layer of ependyma that is continuous with the lining of the ventricle.
  • Superior to this layer is a two-layered fold of pia mater
    
    • ​called the tela choroidea of the third ventricle.
    • The vascular tela choroidea projects downward on each side of the midline, invaginating the ependymal roof to form the choroid plexuses of the third ventricle.
      
      • Within the tela choroidea lie the internal cerebral veins.
  • Superiorly, the roof of the ventricle is related to the fornix and the corpus callosum.
• Inferior wall/ Floor
  
  • Formed by the optic chiasma, the tuber cinereum, the infundibulum, with its funnel-shaped recess, and the mammillary bodies
  • The hypophysis is attached to the infundibulum.
  • Posterior to these structures lies the tegmentum of the cerebral peduncles.

Fourth ventricle

• Single midline ventricle
• Located dorsal to the pons and upper medulla
• Drains into the subarachnoid space via
  
  • Laterally via lateral apertures (foramina of Luschka)
  • Medially via median aperture (foramen of Magendie)

The central canal in the spinal cord

• Has small dilatation at itsinferior end
• Eeferred to as the terminal ventricle

Cerebrospinal Fluid

• In the ventricles of the brain and in the subarachnoid space around the brain and spinal cord.
• It has a volume of about 150 mL.
• Content and color:
  
  • It is a clear, colorless fluid and possesses, in solution, inorganic salts similar to those in the blood plasma.
  • The glucose content is about half that of blood, and there is only a trace of protein.
  • Only a few cells are present, and these are lymphocytes.
• In the lateral recumbent position, the pressure, as measured by spinal tap, is about 60 to 150 mm of water.
  
  • This pressure may be raised by straining, coughing, or compressing the internal jugular veins in the neck
• Function:

1. Cushions and protects the central nervous system from trauma

2. Provides mechanical buoyancy and support for the brain
3. Serves as a reservoir and assists in the regulation of the contents of the skull
4. Nourishes the central nervous system
5. Removes metabolites from the central nervous system
6. Serves as a pathway for pineal secretions to reach the pituitary gland

• Formation
  
  • Mainly in the choroid plexuses of the lateral, third, and fourth ventricles;
  • Some originates from the ependymal cells lining the ventricles: through the perivascular spaces.
  • Produced continuously at a rate of about 0.5 mL per minute and with a total volume of about 150 mL;
  • Production is not pressure regulated (as in the case of blood pressure),
    
    • and it continues to be produced even if the reabsorption mechanisms are obstructed.

Circulation of CSF

• Begins with its secretion from the choroid plexuses in the ventricles.
  
  • From the lateral ventricles
  • Interventricular foramina
  • Into the third ventricle
  • Cerebral aqueduct
  • Fourth ventricle
• The circulation is aided by the arterial pulsations of the choroid plexuses and by the cilia on the ependymal cells lining the ventricles.
  
  • Median aperture and the lateral foramina of the lateral recesses
  • Enters the subarachnoid space
  • Moves through the cerebellomedullary cistern and pontine cisterns
  • Flows superiorly through the tentorial notch of the tentorium cerebelli to reach the inferior surface of the cerebrum
  • Moves superiorly over the lateral aspect of each cerebral hemisphere, assisted by the pulsations of the cerebral arteries.
  • Some of the cerebrospinal fluid moves inferiorly in the subarachnoid space around the spinal cord and cauda equina.
  • Fluid is at a dead end
• Further circulation relies on the pulsations of the spinal arteries and the movements of the vertebral column, respiration, coughing, and the changing of the positions of the body

Absorption

Main sites

• Arachnoid villi that project into the dural venous sinuses
  
  • especially superior sagittal sinus
  • form elevations known as arachnoid granulations.
  • = a diverticulum of the subarachnoid space that pierces the dura mater.
    
    • Capped by a thin cellular layer
    • And covered by the endothelium of the venous sinus.
    • increase in number and size with age and tend to become calcified with advanced age.
• When and how and where does absorption occur?
  
  • When the cerebrospinal fluid pressure exceeds the venous pressure in the sinus.
  • Compression of the tips of the villi closes the tubules and prevents the reflux of blood into the subarachnoid space.???
  • The arachnoid villi thus serve as valves.
  • Where
    
    • Directly into the veins in the subarachnoid space
    • Escapes through the perineural lymph vessels of the cranial and spinal nerves.
• Because the production of cerebrospinal fluid from the choroid plexuses is constant, the rate of absorption of cerebrospinal fluid through the arachnoid villi controls the cerebrospinal fluid pressure.

Hydrocephalus

• Abnormal increase in the volume of the cerebrospinal fluid within the skull.
• Varieties
  
  • Noncommunicating
    
    • raised pressure of the cerebrospinal fluid is due to blockage at some point between its formation at the choroid plexuses and its exit through the foramina in the roof of the fourth ventricle.
  • Communicating
    
    • no obstruction within or to the outflow from the ventricular system;
• Causes
  
  • Excessive Formation of Cerebrospinal Fluid
    
    • Rare ,may occur when there is a tumor of the choroid plexuses.
  • Blockage of the Circulation of Cerebrospinal Fluid
    
    • An obstruction of the interventricular foramen by a tumor will block the drainage of the lateral ventricle on that side.
    • An obstruction in the cerebral aqueduct may be congenital or may result from inflammation or pressure from a tumor.
    • Obstruction of the median aperture (foramen of Magendie) in the roof of the fourth ventricle and the two lateral apertures (foramina of Luschka) in the lateral recesses of the fourth ventricle
  • Diminished Absorption of Cerebrospinal Fluid

Question 8

Brain vessels and blood-brain barrier, brain dysfunctions related to inadequate blood supply via particular blood vessels brain damage due to vascular occlusion

452

484

Answer 8

Blood-Brain and Blood– Cerebrospinal Fluid Barriers

• The central nervous system requires a very stable environment in order to function normally.
• This stability is provided by isolating the nervous system from the blood Blood-Brain Barrier
• The permeability of the blood-brain barrier
  
  • is inversely related to the size of the molecules
  • directly related to their lipid solubility.
  • Gases and water pass readily through the barrier, whereas glucose and electrolytes pass more slowly.
  • The barrier is almost impermeable to plasma proteins and other large organic molecules.
• Structure
  
  • (1) the endothelial cells in the wall of the capillary,
  • (2) a continuous basement membrane surrounding the capillary outside the endothelial cells
  • (3) the foot processes of the astrocytes that adhere to the outer surface of the capillary wall
  • In molecular terms, the blood-brain barrier is thus a continuous lipid bilayer that encircles the endothelial cells and isolates the brain tissue from the blood.
    
    • This explains how lipophilic molecules can readily diffuse through the barrier, whereas hydrophilic molecules are excluded.
    • BBB exists in the newborn, but it is more permeable to certain substances than it is in the adult.
  • Not identical in all regions
    
    • Areas where the blood-brain barrier appears to be absent, the capillary endothelium contains fenestrations across which proteins and small organic molecules may pass from the blood to the nervous tissue

Blood–Cerebrospinal Fluid Barrier:

• There is free passage of water, gases, and lipid-soluble substances from the blood to the cerebrospinal fluid.
• Macromolecules such as proteins are unable to enter the cerebrospinal fluid.
• Structure
  
  • (1) the endothelial cells, which are fenestrated and have very thin walls (the fenestrations are not true perforations but are filled by a thin diaphragm);
  • (2) a continuous basement membrane surrounding the capillary outside the endothelial cells;
  • (3) scattered pale cells with flattened processes; and
  • (4) a continuous basement membrane, on which rest
  • (5) the choroidal epithelial cells )

Blood supply to brain

Circle of Willis

• Union of anterior and posterior circulation
• In the subarachnoid space, in the interpeduncular cistern
• Surrounds optic chiasm and infundibulum
• Anterior circulation: Internal corotid A
  
  • Posterior comminucating A
    
    • Occlusion- little clinical impact if both circulations are working
    • symptoms: occulomotor palsy (close to CN)
      
      • dialliated pupil, ipsilateral
  • Anterior choroidal A
    
    • Supply: BG, internal capsule
    • Occlusion: controlateral hemiplegia
      
      • absense movment and sensory oppotite of lesion
  • Middle cerebral A (MCA)
  • Anterior cerebral A (ACA)
    
    • motor, sensory, will and behaivior areas, LL and pelvis
    • Anterior comminicating A
• Posterior circulation (vertebral A)
  
  • (Anterior spinal A)
  • Posterior inferior CRBL aa
  • Basilar A
    
    • Anterior inferior CRBL A (AICA)
      
      • Facial paralysis and sensory loss (trigeminal N)
    • Laybrinthine A/ auditory A
      
      • accompanies vistibularcochlear N and supplies inner ear
    • Pontine AA
    • Superior CRBL A
    • Posterior CRBL A (PCA)
      
      • inferior and bacl side of brain
      • occipital and inferior temporal cortex
      • deep brain structure

1- Anterior circulation

• Internal carotid arteries (enter skull through carotid canal)
• Anterior cerebral arteries
  
  • Passes above optic chiasm into medial longitudinal fissure
  • Anterior communicating artery
    
    • ​closing circle of willis anteriorlly
  • Medial frontobasal A
  • Polar frontal A
  • Pericallosal A (continuation of Anterior cerebral A)
    
    • Precuneal rr
    • Callosomarginal A
      
      • Cingular branchs
      • Paracentral A
• Middle cerebral arteries
  
  • ​Superior terminal branch
    
    • ​Lateral frontobasal A
    • Prefrontal Sulcus A
    • Precentral sulcus A
    • A of central sulcus/ Rolandic A
  • Inferior terminal branch
    
    • ​Anterior temporal A
    • Medial temporal A
    • Posterior temporal A
    • Branch to angular gyrus
    • Anterior parietal A
    • Posterior parietal A
  • Frontal branchs of middle cerebral A
• Posterior communicating arteries

2- Posterior circuit

• Vertebral arteries
  
  • Basilar artery
    
    • Posterior cerebral arteries
      
      • Medial occipital A
        
        • Calcarine branch
        • Parieto-occipital A
        • Dorsal branch of corpus callosum
• Basilar arteries other ranches:
  
  • pontine branches (pontine arteries)
  • Anterior inferior cerebellar,
    
    • ​inferior surface of the cerebellar hemisphere​
  • Superior cerebellar,
    
    • supplies the pons, midbrain and superior surface of the cerebellum.
  • Internal auditory (Labyrinthine).
  • Becomes the posterior cerebral artery

​

Cerebral Artery Syndromes

• Anterior Cerebral Artery Occlusion
• Contralateral plegia of lower limb​
  
  • Proximal to the anterior communicating artery
    
    • the collateral circulation is usually adequate to preserve the circulation.
  • Occlusion distal to the communicating artery

1. Contralateral hemiparesis and hemisensory loss involving mainly the leg and foot (paracentral lobule of cortex)
2. Inability to identify objects correctly, apathy, and personality changes (frontal and parietal lobes)

• Middle Cerebral Artery Occlusion
• Contralateral hemiplegia more expressed on upper limbs and face, can be aphasia
  
  • Clinical picture will vary according to the site of occlusion

1. Contralateral hemiparesis and hemisensory loss involving mainly the face and arm (precentral and postcentral gyri)
2. Aphasia if the left hemisphere is affected (rarely if the right hemisphere is affected)
3. Contralateral homonymous hemianopia (damage to the optic radiation)
4. Anosognosia if the right hemisphere is affected (rarely if the left hemisphere is affected)

• Posterior Cerebral Artery Occlusion
• Visual field defect: Contralateral homonymous hemianopsy

1. Contralateral homonymous hemianopia

loose same half of visual field from both eyes

2. Visual agnosia (ischemia of the left occipital lobe)

inability to interpret sensations and hence to recognize things

3. Impairment of memory (possible damage to the medial aspect of the temporal lobe)

Internal Carotid Artery Occlusion

1. The symptoms and signs are those of middle cerebral artery occlusion
2. There is partial or complete loss of sight on the same side, but permanent loss is rare
   * (emboli dislodged from the internal carotid artery reach the retina through the ophthalmic artery).

Vertebrobasilar Artery Occlusion

1. Ipsilateral pain and temperature sensory loss of the face and contralateral pain and temperature sensory loss of the body
2. Attacks of hemianopia or complete cortical blindness
3. Ipsilateral loss of the gag reflex, dysphagia, and hoarseness as the result of lesions of the nuclei of the glossopharyngeal and vagus nerves
4. Vertigo, nystagmus, nausea, and vomiting
5. Ipsilateral Horner syndrome
6. Ipsilateral ataxia and other cerebellar signs
7. Unilateral or bilateral hemiparesis
8. Coma

Question 9

Lemniscal system (dorsal column tract), proprioceptive and tactile sensation, sensory loss in spinal cord lesions

Answer 9

The lemniscal system= tr. Spino-bulbo-thalamo-corticalis

General:

• Three-neuron sensitive spinal tract: Direct pathway
• Its function is to transmit information from the receptors of the skin and musculoskeletal system:
  
  • Touch, discriminative sensation: Meissner bodies
    • Dermis, dermal papilae
  • Vibration: Vater-Pacini bodies
  • Static proprioception (tension, pressure, perception of weight, position and body in space): muscle spindle
• The fibers of the track are somatotopically arranged in all sections arranged in all sections

Cell 1 - pseudounipolar cell of the spinal ganglion (tr. Spinobulbaris)

• It starts as a receptor in the periphery, runs through the sensitive spinal nerve to the posterior spinal root.
• It passes through the spinal ganglion without interruption to reach nuceli of dorsal fasciculus
  
  • The fibers have a somatotopic arrangement according to Kahler’s rule :
    
    • Fasciculus gracilis (medially)
      
      • the fibers of the sacral, lumbar and lower thoracic spinal ganglia rise in the
    • Fasciculus cuneatus (laterally)
      
      • the fibers of the upper thoracic and cervical ganglia

*Zones in nuceli:

• Zona glomerularis
  
  • primary fibers: TACTILE SENSATION
• Zona Reticularis
  
  • Secondary fibers, collaterals: STATIC PROPRIOCEPTION
  • part of neurons project in dessending fibers back to spinal cord as bulpospinal tract

Cell 2 - cell in ncl. gracilis a ncl. cuneatus (tr. bulbothalamicus)

• Fibers from glomerular zone:
  
  • Axons of neurons from ncl. gracilis a ncl. cuneatus continue as internal arcuate fibers
  • They decusate at the level of MO, (decussatio lemniscorum) and form the medial lemisinsucs
  • Fibers continue though:
    
    • Pons
    • Midbrain: lateral to ncl ruber
    • into forel field H, then H1 (enter thalamus)
  • The thalamus ends in ncl. ventralis posterolateralis.
• ​Fibers from Reticularis zone:
  
  • ​Posterior thalamic ncl
  • Collaterals:
    
    • Zona incerta, tectum, red ncl, inf olive
    • Bulbo ceerebellar tract: CRBL

Cell 3 -

• Fibers from glomerular zone:
  
  • _​_cell in ncl. ventralis posterolateralis thalamu (tr. thalamocorticalis)
  • The axons of these cells pass through the posterior arm of the internal capsule (radiatio thalami centralis)
  • End in the primary sensitive cortical area (gyrus postcentralis area 3, 1 and 2).
  • S II: 40
• ​Fibers from Reticularis zone:
  
  • ​Posterior thalamic ncl
  • _​_S II: 40
  • Assosiation: 5, 7, 21, 22, 18, 19

This pathway sends collaterals at the level of the second neuron to the cerebellum ( tr. Bulbocerebellaris ), tecta and ncl. ruber

Damage to leminiscal system

• Tactile disturbance (the patient is not able to distinguish the size, shape and surface of the held object)
• Discriminative sensation disorder (inability to distinguish the distance between two points on the skin surface)
• Vibration sensory disorder (the patient does not feel the tuner vibrations on the skin)
• Ataxia (the patient has impaired muscular control, and the movements are jerky or ataxic
• Perceived pain and warmth

Sensory loss in spinal cord lesions

• Central cord syndrome (most common)
  
  • Injury to the central region of the spinal cord (central corticospinal tracts and decussating fibers of the lateral spinothalamic tract)
  • Clinical features
    
    • Bilateral motor paresis​
      
      • the impairment of the extremities is disproportionate since motor fibers supplying the arms are closer to the central part of the corticospinal tract. The leg fibers run more laterally.
    • Variable sensory impairment
      
      • Sometimes burning pain in the arms
      • Sometimes loss of pain and temperature in the arms

Complete Cord Transection Syndrome

• Results in complete loss of all sensibility and voluntary movement below the level of the lesion.
• Fracture dislocation of the vertebral column, by a bullet or stab wound, or by an expanding tumor.

Anterior Cord Syndrome

• Can be caused by:
  
  • Cord contusion during vertebral fracture or dislocation
  • from injury to the anterior spinal artery or its feeder arteries with resultant ischemia of the cord,
  • or by a herniated intervertebral disc.
• Clinical features
  
  • Bilateral:
    • lower motor neuron and muscular atrophy.
    • spastic paralysis below the level of the lesion
    • loss of pain, temperature, and light touch sensations below the level of the lesion
      
      • interruption of the anterior and lateral spinothalamic tracts on both sides.
  • Tactile discrimination and vibratory and proprioceptive sensations are preserved because the posterior white columns on both sides are undamaged.

Central cord syndrome

• Can be caused by:
  
  • hyperextension of the cervical region of the spine
  • The cord is pressed on anteriorly by the vertebral bodies and posteriorly by the bulging of the ligamentum flavum, causing damage to the central region of the spinal cord.
• Clinical features
  
  • Bilateral
    
    • lower motor neuron paralysis in the segment of the lesion and muscular atrophy.
    • spastic paralysis below the level of the lesion with characteristic sacral “sparing.”
    • loss of pain, temperature, light touch, and pressure sensations below the level of the lesion with characteristic sacral “sparing.”

Brown-Séquard Syndrome or Hemisection of the Cord

• paralysis of one side of the body
• Clinical features
  
  • Motor: Ipsilateral
    
    • lower motor neuron paralysis in the segment of the lesion and muscular atrophy.
    • spastic paralysis below the level of the lesion.
  • Sensory
    
    • Ipsilateral band of cutaneous anesthesia in the segment of the lesion.
    • Ipsilateral loss of tactile discriminationand ofvibratoryandproprioceptive sensationsbelow the level of the lesion.
      
      • Destruction of the ascending tracts in the posterior white column on the same side of the lesion.
    • Contralateral loss of pain and temperature sensations below the level of the lesion.
      
      • This is due to destruction of the crossed lateral spinothalamic tracts on the same side of the lesion. Because the tracts cross obliquely, the sensory loss occurs two or three segments below the lesion distally.
    • Contralateral but not complete loss of tactile sensation below the level of the lesion.

Syringomyelia

• Caused by:
  
  • Developmental abnormality in the formation of the central canal
• Clinical features
  
  • Loss of pain and temperature sensations in dermatomes on both sides of the body related to the affected segments of the cord.
  • This loss commonly has a shawllike distribution caused by the interruption of the lateral spinothalamic tracts as they cross the midline in the anterior gray and white commissures.
  • Tactile discrimination, vibratory sense, and proprioceptive sense are normal.

LATERAL MEDULAARY SYNDROME

Poliomyelitis

• acute viral infection of the neurons of the anterior gray columns of the spinal cord and the motor nuclei of the cranial nerves.
• Following death of the motor nerve cells, there is paralysis and wasting of the muscles.
• The muscles of the lower limb are more often affected than the muscles of the upper limb.
• The muscles of the face, pharynx, larynx, and tongue may also be paralyzed.

Question 10

Anterolateral system of sensitive spinal tracts - (spinothalamic, spinoreticular and spinotectal tracts), pain pathways

Answer 10

General:

• Includes three pathways leading to touch, heat and pain from the body
  
  • tr. spinothalamicus
  • tr. spinoreticularis
  • tr. spinotectalis
• They run through the spinal cord in the lateral and anterior spinal cords

1-Tr. spinothalamicus

Fast pain: sharp, penetrating and cutting pain from contralateral side of body

• Anterior: Pressure, Crude touch
• Lateral: Pain, Temperature

Aδ fibers

• Neospinothalamic pathway “young”
  
  • most to thalamus
  • Afferent: pain (e.g., thermal, mechanical-touch, pressure )
    
    • Free nerve endings
    • Responsible for the withdrawal response to pain (e.g., rapidly moving the hand when burned)
• Secondary spinothalamic fibers- C fibers:
  
  • slow pain- least mylinated
    
    • Afferent: pain (e.g., chemical, thermal, mechanical)
    • dull hard to localize pain, from larger body areas
    • more synapses
  • paliospinothalamic pathway “old”
    
    • 80% terminate in RF
    • rest go to thalamus, non specific ncl

The first neuron has a body in ggl. spinal.

The second neuron

• Enter the spinal cord, they either descend or ascend a few vertebral levels.
• This is achieved by travelling via Lissauer’s tract-
  
  • which is a collection of descending and ascending collaterals of the primary neurons.
• Next the neurons will synapse with the secondary neurons in one of two areas of the spinal cord:
• The substantia gelatinosa or the nucleus proprius
  
  • Rexed lamina IV. and V.
  • The axons of the second neuron intersect in the respective spinal cord segment,
    
    • therefore they have the opposite somatotopic arrangement than the previous pathway - the fibers in the neck are the most medial.
  • The strain passes laterally from the medial lemniscus
  • Forel field H1- into thalamus

Third neuron (ncl-> internal capsule-> corona radiata)

• Ncl . ventralis posterolateralis thalami
  
  • S I, S II
• Posterior thalamic ncl
  
  • S II, assosiation: occipital, temporal, parietal
• Intralaminares ncl
  
  • Frontal cortex

2-Spinoreticular tract

• Mainly leads to “slow pain”.
• Responsible for increasing our level of arousal/alertness in response to the pain or temperature.
• It phylogenetic older than the previous path, dominated by unmyelinated C fiber
• The first neuron
  
  • is a pseudounipolar spinal ganglion neuron.
• The second neuron
  
  • is located in the posterior spinal cord
  • some of its axons intersect and run in the anterior and lateral spinal cords.
• Terminates in medial nuclei of the reticular formation
  
  • link to reticulo-hypothalamic pathway:
    
    • lateral hypothalmus (MFB), terminating in middle and posterior hypothalamus
    • and from this path continues to ARAS - ascending activating system of the reticular formation.
  • link to reticulo thalamic pathway:
    
    • around red ncl, cia filed H1
    • Thalamus: to post ncll, intralaminar ncl, mediani ncl
      
      • intralaminar ncll to frontal lobe and whole cortex via assoaiation connections
        
        • activating system

​3-Spinoreticular tract

• Enables us to orient our eyes and move our head toward the relevant stimulus.
  
  • Conducts stimuli from the skin to the tecta, where they integrate with visual and auditory information in the superior and inferior colliculus .
• The fibres ascend to synapse in the superior colliculi of the midbrain.
  
  • functional parts of superior colliculus
    
    • upper layers: visual
    • lower: somatic (incoming projections from spinal cords, cortical FEF…)

Clinical

Lateral Spinothalamic Tract

• Destruction of this tract produces contralateral loss of pain and thermal sensibilities below the level of the lesion.
• The patient will not, therefore, respond to pinprick or recognize hot and cold objects placed in contact with the skin.

Anterior Spinothalamic Tract

• Destruction of this tract produces contralateral loss of light touch and pressure sensibilities below the level of the lesion.
• Remember that discriminative touch will still be present, because this information is conducted through the fasciculus gracilis and fasciculus cuneatus.
• The patient will not feel the light touch of a piece of cotton placed against the skin or feel pressure from a blunt object placed against the skin.

Pain

Types of pain

• Nociceptive pain: pain that is triggered by chemical, mechanical, or thermal stimuli
  
  • Somatic pain (musculoskeletal pain)
    
    • Localized, sharp pain
    • Variable in duration and quality
  • Visceral pain
    
    • Dull, deep, diffuse pain
• Neuropathic pain: pain caused by abnormal neural activity that arises secondary to injury, disease, or dysfunction of the nervous system
  
  • Central pain: caused by CNS dysfunction (e.g., from lesions produced by an ischemic stroke, phantom limb pain)
  • Peripheral pain: caused by damage to peripheral nerves (e.g., diabetic neuropathy, postherpetic neuralgia)
  • Sympathetically mediated pain: caused by damage to autonomic nerves (e.g., complex regional pain syndrome)
• Referred pain
  
  • Definition: pain that is perceived at a location other than that of the causative stimulus; projection of pain usually onto a specific dermatome or myotome of the corresponding segment of the spinal cord

Pain

• All types of pain reception take place in free nerve endings.
  
  • Fast pain is experienced by mechanical or thermal types of stimui
    
    • Aδ fibers
    • The fast pain impulses reach consciousness first to alert the individual to danger so that a suitable protective response may take place.
  • Slow pain may be elicited by mechanical, thermal, and chemical stimuli.
    
    • C fibers
    • Slow pain is appreciated later and lasts much longer.
• Chemical substance that excite free nerve endings.
  
  • serotonin;
  • histamine;
  • bradykinin; acids, such as lactic acid; and K ions.
• The threshold for pain endings can be lowered by prostaglandins and substance P, but they cannot stimulate the endings directly by themselves.

The individual should be aware of the existence of stimuli that, if allowed to persist, will bring about tissue destruction; pain receptors have little or no adaptation.

• The cingulate gyrus is involved with the interpretation of the emotional aspect of pain,
• Insular gyrus is concerned with the interpretation of pain stimuli from the internal organs of the body and brings about an autonomic response.

Question 11

Corticospinal (pyramidal) and corticonuclear tract

Extrapyramidal trycts
– tr. reticulospinalis – gamma moto-neurons – tr. vestibulospinalis – postural muscles
– tr. rubrospinalis (rudimentary)

Extrapyramidal tracts

– tr. reticulospinalis, vestibulospinalis, tectospinalis, rubrospinalis, interstitiospinalis

– raphaespinalis, caerulospinalis

Answer 11

Direct Motor pathways:

• Corticospinal Tracts:
  
  • Voluntary movement of the contralateral side
• corticonuclear Tr

Corticospinal

• Origin: (V cortical layer)
  
  • Precentral gyrus:
    
    • primary motor cortex (area 4),
    • secondary motor cortex (area 6),
    • area 4,6
  • Postcentral gyrus
    
    • parietal lobe (areas 3, 1, and 2)
    • cortical control circuit
  • Homunculus “stands upsidedown ma”
    
    • Topographical arrangment
      
      • Region controlling the face is situated inferiorly,
      • Tegion controlling the lower limb is situated superiorly and on the medial surface of the hemisphere.
  • Majority of the corticospinal fibers are myelinated and are relatively slow-conducting, small fibers.
• Course:
  
  • Descending fibers converge in the corona radiata
  • Pass through the posterior limb of the internal capsule
    
    • Closest to the genu: cervical body,
    • Posteriorly: lower extremity
  • Enter crura cerebri/ Cerebral peduncle?
    
    • Located in middle
      
      • On each side- cortico pontine fibers
    • At upper rim the cortico- nuclear tr fibers break of to relevant ncl
  • Enter basal portion of pons
    
    • tract is broken into many bundles by the transverse pontocerebellar fibers
  • In the medulla oblongata, the bundles become grouped together along the anterior border to the pyramid
    
    • some fibers break of to sensory and CN
  • Junction of the medulla oblongata and the spinal cord,
    
    • 80% cross in pyramidal deccusation
      
      • enter lateral funiculi
      • nck of dorsal funiculi?
    • 20% ventral cortico spinal Tr
      
      • ipsilateral ventral funiculi
• Terminations:
  
  • tr. corticospinalis lat.
    • 80% of the fibers that crossed in the decussation pyramidum
      
      • Crosses in the caudal medulla (pyramidal decussation)
      • Descends in the spinal cord contralaterally
    • ending in the interneurons and α-motoneurons of the anterior spinal horns.
    • These neurons mainly activate the distal limb muscles.
  • tr. corticospinalis ant
    • The remaining 20% ​ uncrossed
    • Crosses at the same level of the spine as it innervates (not at the level of the medulla oblongata)
    • It controls the axial and proximal limb muscles.

Corticonuclerar tract DEGESHIM:

• Ncl. n. trigemini :
  
  • the fibers are uncrossed.
  • Part for free movements of the masticatory muscles.
• Ncl. n. facialis :
  
  • crossed and uncrossed fibers.
  • Free facial expressions of forehead muscles, eye slits, lower facial mimic muscles.
• Ncl. ambiguus (n. glossopharyngeus, n. vagus ).
  
  • Free movements during swallowing and phonation.
• Ncl. N. Accessorii (part of ncl. Ambiguus).
  
  • For free movement of laryngeal muscles.
• Ncl. n. hypoglossi .
  
  • Free movements of the muscles of the tongue.
  • controlled by controlateral cortex
• Nuclei of oculomotor nerves - n. III , n. IV , n. VI .

Clinical:

Types of Paralysis

• Hemiplegia is a paralysis of one side of the body and includes the upper limb, one side of the trunk, and the lower limb.
• Monoplegia is a paralysis of one limb only.
• Diplegia is a paralysis of two corresponding limbs (i.e., arms or legs).
• Paraplegia is a paralysis of the two lower limbs.
• Quadriplegia is a paralysis of all four limbs.

Hemiplegia alternans superior/ Weber syndrome

• Vascular Lesions of the Midbrain
• Commonly produced by occlusion of a branch of the posterior cerebral artery
• Results in the necrosis of brain tissue involving the oculomotor nerve and the crus cerebri
• Pyramidal tract: contralateral hemiparasis
• Palsy of n. III: There is ipsilateral ophthalmoplegia and contralateral paralysis of the lower part of the face, the tongue, and the arm and leg.
  
  • The eyeball is deviated laterally because of the paralysis of the medial rectus muscle; there is drooping (ptosis) of the upper lid, and the pupil is dilated and fixed to light and accommodation.

Benedikt Syndrome

• Similar to Weber syndrome, but the necrosis involves the medial lemniscus and red nucleus,
• producing contralateral hemianesthesia and involuntary movements of the limbs of the opposite side.

Syndroma medullare mediale Dejerine

• Lesion of a. vertebralis
  
  • paresis contralateralis (tractus pyramidalis)
  • contralateral lesion of fine sensitivity and proprioception (lemniscus medialis – tr. bulbothalamocorticalis)
  • hemiglossoplegia ipsilateralis (n. XII)

Syndroma medullare laterale Wallenbergi

• Lesion of a. cerebelli posterior inferior
  
  • dysphagia + dysarthria ipsilateralis (ncl. ambiguus)
  • analgesia + thermoanaesthesia capitis ipsilateralis (ncl. + tractus spinalis n. V)
  • vertigo, nausea, vomitus, nystagmus (ncll. vestibulares)
  • syndroma Claude Bernard-Horner ispilaterale (descending sympatetic fibers)
  • Ipsilateral lesion of cerebellum
  • analgesia + thermoanaesthesia contralateralis corporis (tractus spinothalamicus – lemniscus spinalis)

Locked-in syndrom

• Awake patient
  
  • Whole kvadrupalsy + palsy of cranial nerves up from n.V
  • Lesion of pars basilaris pontis = closure of a. basilaris
  • Sometimes preserved proprioception and sensitivity from body

Question 12

Motor pathways in spinal cord and motor deficiencies in spinal cord lesions

Answer 12

Corticospinal tracts

• pathways concerned with voluntary, discrete, skilled movements, especially those of the distal parts of the limbs.

Reticulospinal tracts

• facilitate or inhibit the activity of the alpha and gamma motor neurons in the anterior gray columns and may, therefore, facilitate or inhibit voluntary movement or reflex activity.

Tectospinal tract is

• concerned with reflex postural movements in response to visual stimuli.
• Those fibers that are associated with the sympathetic neurons in the lateral gray column are concerned with the pupillodilation reflex in response to darkness.

Rubrospinal tract

• aacts on both the alpha and gamma motor neurons in the anterior gray columns and facilitates the activity of flexor muscles and inhibits the activity of extensor or antigravity muscles.

Vestibulospinal tract

• by acting on the motor neurons in the anterior gray columns, facilitates the activity of the extensor muscles, inhibits the activity of the flexor muscles, and is concerned with the postural activity associated with balance.

Olivospinal tract

• may play a role in muscular activity, but there is doubt that it exists. The descending autonomic fibers are concerned with the control of visceral activity.

Motor function areas

• Primary motor area
  
  • is active in the implementation of the movement itself, it is mainly influenced by the cerebellum
• Premotor area ,
  
  • Triggered by motion planning (and even by mere imagination) and is strongly influenced by the basal ganglia
  • It is said to be used in the implementation of more complex movements and complex movement patterns
• Complementary motor area
  
  • participates in the activation of the axial muscles and the proximal muscles of the limbs (postural muscles), during the realization of bilateral movements
  • It realizes more complex movement patterns.
  • Also affected by the basal ganglia. It is also said to integrate sensitive information, use memory traces, and participate in eye-head alterations.
• There are also specific cortical areas designated for a specific activity, eg Broc’s speech center, frontal eye field, head rotation area, manual skills area

Clinical:

Types of Paralysis

• Hemiplegia is a paralysis of one side of the body and includes the upper limb, one side of the trunk, and the lower limb.
• Monoplegia is a paralysis of one limb only.
• Diplegia is a paralysis of two corresponding limbs (i.e., arms or legs).
• Paraplegia is a paralysis of the two lower limbs.
• Quadriplegia is a paralysis of all four limbs.

Lower motor neuron lesions (poliomyelitis or nerve lesion)

• Muscle tone and stretch and tendon reflexes are reduced or absent (flaccid paralysis)
• Progressive atrophy of muscles occurs
• EMG detects fibrillation potentials caused by isolated contrations of denervated muscles
• In partially denervated muscles, the inervation is being renewed

Upper motor neuron lesions (bleeding in capsula interna or transected spinal cord)

• Muscle tone and stretch and tendon reflexes are increased (spastic paralysis)
• Superficial reflexes (abdominal and cremasteric ones) are extinct
• An abnormal plantar Babinski reflex occurs
• Voluntary movements are reduced or absent

Hemiplegia alternans superior/ Weber syndrome

• Vascular Lesions of the Midbrain
• Commonly produced by occlusion of a branch of the posterior cerebral artery
• Results in the necrosis of brain tissue involving the oculomotor nerve and the crus cerebri
• Pyramidal tract: contralateral hemiparasis
• Palsy of n. III: There is ipsilateral ophthalmoplegia and contralateral paralysis of the lower part of the face, the tongue, and the arm and leg.
  
  • The eyeball is deviated laterally because of the paralysis of the medial rectus muscle; there is drooping (ptosis) of the upper lid, and the pupil is dilated and fixed to light and accommodation.

Hemiplegia alternans media

• Basialr artery

Hemiplegia alternans inferior

• Anterior spinalis

Wallenberg´s sy of lateral medulla oblongata

• Post inf cerebral

Benedikt Syndrome

• Similar to Weber syndrome, but the necrosis involves the medial lemniscus and red nucleus,
• producing contralateral hemianesthesia and involuntary movements of the limbs of the opposite side.

Syndroma medullare mediale Dejerine

• Lesion of a. vertebralis
  
  • paresis contralateralis (tractus pyramidalis)
  • contralateral lesion of fine sensitivity and proprioception (lemniscus medialis – tr. bulbothalamocorticalis)
  • hemiglossoplegia ipsilateralis (n. XII)

Syndroma medullare laterale Wallenbergi

• Lesion of a. cerebelli posterior inferior
  
  • dysphagia + dysarthria ipsilateralis (ncl. ambiguus)
  • analgesia + thermoanaesthesia capitis ipsilateralis (ncl. + tractus spinalis n. V)
  • vertigo, nausea, vomitus, nystagmus (ncll. vestibulares)
  • syndroma Claude Bernard-Horner ispilaterale (descending sympatetic fibers)
  • Ipsilateral lesion of cerebellum
  • analgesia + thermoanaesthesia contralateralis corporis (tractus spinothalamicus – lemniscus spinalis)

Locked-in syndrom

• Awake patient
  
  • Whole kvadrupalsy + palsy of cranial nerves up from n.V
  • Lesion of pars basilaris pontis = closure of a. basilaris
  • Sometimes preserved proprioception and sensitivity from body

The Descending Tracts of the Spinal Cord

The motor neurons situated in the anterior gray columns of the spinal cord send axons to innervate skeletal muscle through the anterior roots of the spinal nerves.

Referred to as the lower motor neurons

These supraspinal neurons and their tracts

Upper motor neurons,

Provide numerous separate pathways that can influence motor activity

Corticonuclerar tract DEGESHIM:

• Ncl. n. trigemini :
  
  • the fibers are uncrossed.
  • Part for free movements of the masticatory muscles.
• Ncl. n. facialis :
  
  • crossed and uncrossed fibers.
  • Free facial expressions of forehead muscles, eye slits, lower facial mimic muscles.
• Ncl. ambiguus (n. glossopharyngeus, n. vagus ).
  
  • Free movements during swallowing and phonation.
• Ncl. N. Accessorii (part of ncl. Ambiguus).
  
  • For free movement of laryngeal muscles.
• Ncl. n. hypoglossi .
  
  • Free movements of the muscles of the tongue.
  • controlled by controlateral cortex
• Nuclei of oculomotor nerves - n. III , n. IV , n. VI .

Question 13

Limbic system - connections and function (cortical areas, hippocampal formation, amygdalar complex)

322

Answer 13

General:

• Collection of neuronal pathways from different anatomical parts of the brain
• Consists of cortical and subcortical structures
  
  • 1- Cortical: medial aspect of hemispheres
  • 2- Subcortical: in BG, diencephalon, brainsptem, RF
• Function:
  
  • Emotions, memory, sextual behavior, social behavior management of homeostasis, memories, attention

1- Limbic cortical area (lobe limbicus)

• Neocortical field - (anterior to posterior)
  
  • Gyrus subcallosus
  • Gyrus cinguli
    
    • Area 23-25,29-31
    • Function:
      
      • Ventral part: emotional reactions
      • Dorsal part: verbal memory and spatial orientation
    • AF: association areas of temporal, parietal and occipital lobe
    • EF: feedbacks to cortex and subcortical areas (striatum, thalamus, cerebellum)
    • Cingulum –
      
      • tract leading to gyrus parahippocampalis
      • Forms part of the Papez circuit
      • Also penetrates into the subcortical structures - mainly into
        
        • the striatum,
        • cerebellum (via the nuclei pontis),
        • thalamus (anterior cingular area into the medial and intralaminar nuclei, posterior to the lateral, anterior and pulvinar nuclei).
  • Gyrus parahippocampalis
    
    • Structures:
      • Area entorhinalis (area 28)
      • Area perirhinalis (area 35, 36)
      • Uncus – rostrally
    • Spatial memory, orientation and ability to distinguish and recognize objects
    • AF: association areas, hippocampal formation, corpus amygdaloideum, thalamus
    • EF: hippocampal formation, corpus amygdaloideum, thalamus (ncl. anteriores)
• Mesocortical or transitional field
  
  • entorhinal cortical area (28)
  • perirhinal cortical area
  • praesubiculum?
• Archicortical field
  
  • Posterior commisural hippocampus has 3 major cortical fields= AKA: hippocampal formation
  • Function: storing of information into long-term memory (consolidation of memory trace)
    
    • Subiculum
      
      • in depth of hapocampal sulcus
      • located on the upper side of the parahippocampalis gyrus,
      • medially from it is the entorhinal cortical area and the praesubiculum (mesocortex),
      • laterally it passes into the hippocampus.
    • Cornu ammonis: “hippocampus proper”
      
      • archs into lateral ventricle
      • the largest volume structure of a hippocampal formation
      • consisting of 4 units (CA1 - CA4).
      • At the upper edge, a bundle of fornix fibers (fimbria fornicis) begins, connecting the hippocampal formation with the rest of the limbic system.
    • Dentate gyrus
      
      • In hippocampal sulcus
      • Seperated from hippocampus via choroid fissure ??
      • Medially from the hippocampus
      • Mostrally gets narrower and terminates as oblique taenia Giacomini
      • Continues as gyrus fasciolaris and further into indusim griseum as striae longitudinales corporis callosi
• Paleocortical field -
  
  • Olfactory cortical area
    
    • ambient gyrus?

2- Subcortical limbic structures

• Amygdala
  
  • = nucleus amgydalae = archistriatum
  • morphologically and developmentally basal ganglion
  • functionally and connected to limbic system
  • Location:
    
    • within temporal lobe
    • rostral to cornu inferius ventriculi lateralis and to cauda ncl. caudati
  • Complex of nuclei
    
    • Younger = baso-lateral part
      
      • connection to cortex
      • 70% of volume
    • Central nuclei -
      
      • are small, deposited dorsally, under the influence of brainstem structures
    • Older = cortico-centromedial part/ncl
      
      • ​connection to olfactory areas, hypothalamus and brainstem
      • on the surface of the uncus
    • Cortex periamygdalaris
  • The amygdala releases two important bundles of predominantly efferent fibers:
    
    • The ventral amygdalofugal system
      
      • From the basolateral part
      • to the thalamus , hypothalamus , brainstem, and cortex;
    • Stria terminalis
      
      • From the corticomedial part
      • Through the nucleus caudatus and thalamus arcuately to the hypothalamus.
  • The amygdala has very rich connections and when it is irritated we can observe a reaction of “increased attention” and vice versa, in bilateral damage, fear and anxiety disappear. It can say that the amygdala are part of a defense mechanism, which is capable of evaluating the “dangerousness” of an approaching object or other organism [3] The amygdala also decides on the positive or negative “breathe” the perception and is considered the “center of epilepsy.”
• Septum verum
• Much of the hypothalamus
• Thalamus nuclei
• Habenula nuclei (epithalamus)
• Some nuclei of reticular formation
• Striatum and ventidal pallidum

Question 14

406 HYPOTH

Question 15

Neurotransmitters in the CNS, main brain chemical systems

Answer 15

Chemical pathways:

• In addition to normal pathways, there are also chemical pathways in the brain.
• Chemical mediators flow through these pathways through neurons, helping and stimulating CNS function .
• Mediators are highly specific substances and often affect specific areas of the brain.

Noradrengeric system

serotonegeris system

Transmitters

• Neurotransmitters: direclty involved in stimulation or inhibition
• Neuromodulators: influence these activites
• Neurohormones:
• Can be monoamines, amino acids, peptides, hypophyseal

Main Chemical systems:

A-Monoaminergic, divided in subsystems accroding to chemical activities of cells

1-Catecholaminergic system

• located on discontinuous line in lateral tegmentum of brain stem, continue rostarly as far as hypothalamus
• A1-10 in brainstem
• A11-15 in hypothalamus ​
• Noradrenaline A1-7, A11-15
  
  • Neurons: in RF of the pontoon and MO
  • Locus coeruleus (A7)
  • Largest and most important
  • located below the base IV. brain chambers.
  • The descending fibers go to the anterior and posterior corners of the spinal cord, to the sensitive nuclei of the cranial nerves and to the cerebellum, where they end at the dendrites of Purkinje cells.
  • The ascending fibers end mainly in the hypothalamus and thalamus (in nc. VPL and nc. VPM). Strong projections also point to the neocortex and hippocampal formation. Noradrenergic fibers do not enter the striatum and pallida.
  • Function:
    
    • innervation of small cerebral vessels and regulation of cerebral circulation
    • Noradrenergic fibers are part of the activating ascending system of the Reticular Formation
• Dopamine A8-10
  
  • Substantia nigra - pars compacta (A9)
    
    • fibers project into the striatum and, to a lesser extent, into the globus pallidus.
  • Area tegmentalis ventralis (A10) (medially from it)
  • Fibers emerging from the area tegmentalis ventralis form the so-called mesolimbic dopaminergic system and terminate in the striatum ventrale, pallidum ventrale, septum verum, amygdala and cerebral cortex, mainly in the prefrontal and primarily motor areas.
• Adrenergic: near A1-3, in C1-3???

2- Serotonergic

• system of „mood and anxiety“
• located amaong nuclei of raphe system, B1-B7 (ncll. raphes)
• B6: ncl raphe dorsalis, B8 ncl linearius caudalis?
• Neurons stored in the raphe nuclei of the reticular formation .
• Their axons reach all cortical areas / all structures of the limbic system, also striatum, thalamus, hypothalamus, brainstem, cerebellum and spinal cord.
• Function:
  
  • activity in the ascending component causes mood swings and behavioral disorders
  • the fibers ending in the posterior corner of the spinal cord affect the transmission of painful signals , their stimulation causes analgesia
    
    • tractus raphespinalis – suppression of pain transmission in posterior horns of spinal cord
  • Decreased serotonin synthesis causes depression, sleep disorders and insomnia

B- Cholinergic system

• Neurons synthesizing acetylcholine.
• Nuclei stored in the hemispheres and in the trunk.
  
  • Septum verum Ch 1-3
    
    • Ch1: to hippocampus and corpus amygdaloideum
    • Ch3: limbic system
  • Nucleus basalis (Meynerti), belonging to the basal ganglia, Ch4
    
    • To cerebral cortex, hippocampus and corpus amygdaloideum
    • Behavior and cognitive function (consciousness, memory, learning)
  • In brainstem, apart of RF
    
    • Ch5: ncl pedunculo-pontinus
    • Ch6: ncl latero-dorsalis
    • Part of ARAS (extrapyramidal motorics and limbic circuits)
• Excitatory effect on neurons and is mainly released at the presynaptic terminals of the neocortex, where it facilitates transmission at excitatory cortical synapses.

C- Histaminergic

• histamine (H)
• Posterior hypothalamus
  
  • transmission of pain, motorics, thermoregulation, biorythms, food and fluids intake
• ncl. tuberomammillaris
  
  • to cortex and medulla
  • vigilance-sleep cycle
  • supply of histamine is crucial for arousal

D- Glutamatergic

• Principal excitatory mediator of CNS
• Majority of tracts and circuits
  
  • ncl. subthalamicus
  • Neurons of cerebral and cerebellar cortex

E- GABAergic

• gama-aminobutyric acid (GABA)
• Principal inhibitory mediator of CNS – glycine in medulla !
• Majority of cortical and subcortical structures

Excitatory neurotransmitters

• Glutamate (Glu)
• Acetylcholine (ACh)
• Histamine
• Dopamine (DA)
• Norepinephrine (NE); also known as noradrenaline (NAd)
• Epinephrine (Epi); also known as adrenaline (Ad)

Inhibitory neurotransmitters

• gamma-Aminobutyric acid (GABA)
• Serotonin (5-HT)
• Dopamine (DA)

Neuromodulators

• Dopamine (DA)
• Serotonin (5-HT)
• Acetylcholine (ACh)
• Histamine
• Norepinephrine (NE)

Neurohormones

• Releasing hormones from hypothalamus
• Oxytocin (Oxt)
• Vasopressin; also known as antidiuretic hormone (ADH)

Question 16

Auditory pathway

Answer 16

Vestibulocochlear Nerve (Cranial Nerve VIII)

• vestibular nerve
• cochlear nerve,
• which are concerned with the transmission of afferent information from the internal ear to the central nervous system

Vestibular Nerve

• Utricle and saccule→ (that provide information concerning the position of the head)
• Semicircular canals → (provide information concerning movements of the head)
• Vestibular ganglion: which is situated in the internal acoustic meatus.

Enter the anterior surface of the brainstem in a groove between the lower border of the pons and the upper part of the medulla oblongata→ vestibular nuclear complex:

• NCL
  
  • (1) the lateral vestibular nucleus,
  • (2) the superior vestibular nucleus,
  • (3) the medial vestibular nucleus,
  • (4) the inferior vestibular nucleus

Four nuclei beneath the floor of the fourth ventricle

• AF
  
  • Vestibular nerve: the utricle and saccule and the semicircular canals
  • Fibers from the cerebellum through the inferior cerebellar peduncle
  • Cerebral cortex, to the vestibular area in the postcentral gyrus just above the lateral fissure.
    
    • These fibers are thought to relay in the ventral posterior nuclei of the thalamus.
    • The cerebral cortex probably serves to orient the individual consciously in space.
• EF
  
  • Cerebellum through the inferior cerebellar peduncle.
  • • bypassing the vestibular nuclei.
  • Vestibulospinal tract: Descend uncrossed to the spinal cord from the lateral vestibular nucleus
  • Medial longitudinal fasciculus: To the nuclei of the oculomotor, trochlear, and abducent nerves

These connections enable the movements of the head and the eyes to be coordinated so that visual fixation on an object can be maintained.

In addition, information received from the internal ear can assist in maintaining balance by influencing the muscle tone of the limbs and trunk.

Cochlear Nerve

The cochlear nerve conducts nerve impulses concerned with sound from the organ of Corti in the cochlea.

The fibers of the cochlear nerve are the central processes of nerve cells located in the spiral ganglion of the cochlea

Enter the anterior surface of the brainstem at the lower border of the pons on the lateral side of the emerging facial nerve and are separated from it by the vestibular nerve

On entering the pons, the nerve fibers divide, with one branch entering the posterior cochlear nucleus and the other branch entering the anterior cochlear nucleus.

Cochlear Nuclei

The anterior and posterior cochlear nuclei

situated on the surface of the inferior cerebellar peduncle

AF

cochlea through the cochlear nerve.

trapezoid body and the olivary nucleus.

The cochlear nuclei send axons (second-order neuron fibers) that run

medially through the pons to end in the trapezoid body and the olivary nucleus.

Here, they are relayed in the posterior nucleus of the

trapezoid body and the superior olivary nucleus on the same or the opposite side. The axons now ascend through the posterior part of

the pons and midbrain and form a tract known as the lateral lemniscus (Fig. 11-14). Each lateral lemniscus, therefore, consists of thirdorder

neurons from both sides. As these fibers ascend, some of them relay in small groups of nerve cells, collectively known as the nucleus

of the lateral lemniscus (Fig. 11-14).

On reaching the midbrain, the fibers of the lateral lemniscus either terminate in the nucleus of the inferior colliculus or are relayed in

the medial geniculate body and pass to the auditory cortex of the cerebral hemisphere through the acoustic radiation of the internal

capsule (Fig. 11-14).

The primary auditory cortex (areas 41 and 42) includes the gyrus of Heschl on the upper surface of the superior temporal gyrus. The

recognition and interpretation of sounds on the basis of past experience take place in the secondary auditory area.

Nerve impulses from the ear are transmitted along auditory pathways on both sides of the brainstem, with more being projected along the

contralateral pathway. M any collateral branches are given off to the reticular activating system of the brainstem (see p. 307). The

tonotopic organization present in the organ of Corti is preserved within the cochlear nuclei, the inferior colliculi, and the primary

auditory area.

Descending Auditory Pathways

Descending fibers originating in the auditory cortex and in other nuclei in the auditory pathway accompany the ascending pathway. These

fibers are bilateral and end on nerve cells at different levels of the auditory pathway and on the hair cells of the organ of Corti. It is

believed that these fibers serve as a feedback mechanism and inhibit the reception of sound. They may also have a role in the process of

auditory sharpening, suppressing some signals and enhancing others.

Question 17

Visual pathway and visual cortical areas

→

227

357

356

378

428

435 visual reflex

​

• oculomotor nucleus pass anteriorly through the red nucleus to emerge on the medial side of the crus cerebri in the interpeduncular fossa. The nucleus of the oculomotor nerve is divisible into a number of cell groups.

Answer 17

Visual pathway:

General

• Sight: Special sense transmitted by cranial nerve II, the optic nerve.
  
  • Leaves the skull via the optic canal,
• A direct structure of the brain, and not technically a distinct cranial nerve like the other 11 pairs.
• Lens is converging: inverts all objects in visual field
  
  • Medial part of retina recieves temportal 1/2 (lateral) of visual field
  • Lateral part of retina recieves nasal 1/2 (medial) of visual field
• 4 neuron tract
  
  • 1- neuron: rods and cones of the retina
  • 2- neuron: bipolar cells of the retina (horizontal cell, amacrine???)
  • 3- neuron: ganglion cells of the retina - n. II - optic chiasma -
  • 4- neuron:lateral geniculate body
• neuron: cells in the lateral geniculate body - tractus geniculocorticalis- inerpolalated??? (= radiatio optica Gratioleti) - lobus ocipitalis, area 17 (around the sulcus calcarinus)
• • Unite together at the optic chiasm that lies superior to the pituitary gland (which lies in the sella turcica).

The peripheral fields/nasal retinal fields cross over at the chiasm. The optic tracts then travel to synapse in the lateral geniculate nucleus of the thalamus, and from there they travel through Meyer’s loop (from inferior retina/superior visual field) and Baum’s loop (from the superior retina/inferior visual field). From there, they go to the primary visual cortex.

Course of visual pathway

Optic part of retina → optic n. → optic chiasma → optic tract → lateral geniculate body: interpolation→ optic ratiation: primary visual area BA17

1-Origin of the Optic Nerve

• Fibers of the optic nerve are the axons of the cells in the ganglionic layer of the retina.
• They converge on the optic disc and exit from the eye, about 3 or 4 mm to the nasal side of its center, as the optic nerve
• The fibers of the optic nerve are myelinated,
  
  • Formed from oligodendrocytes rather than Schwann cells, since the optic nerve is comparable to a tract within the central nervous system.
• The optic nerve leaves the orbital cavity through the optic canal and unites with the optic nerve of the opposite side to form the optic chiasma.

2-Optic Chiasma

• Situated at the junction of the anterior wall and floor of the third ventricle.
• In the chiasma,
  
  • Fibers from the nasal (medial) half of each retina, including the nasal half of the macula,
    
    • Cross the midline and enter the optic tract of the opposite side,
  • Fibers from the temporal (lateral) half of each retina, including the temporal half of the macula,
    
    • pass posteriorly in the optic tract of the same side.

3-Optic Tract

• Emerges from the optic chiasma and passes posterolaterally around the cerebral peduncle.
• Fiber terminations:
  
  • Most: synapsing with nerve cells in the lateral geniculate body
    
    • which is a small projection from the posterior part of the thalamus.
  • Some: collaterals

4-Lateral Geniculate Body

• Small, oval swelling projecting from the pulvinar of the thalamus.
• It consists of six layers of cells, on which synapse the axons of the optic tract.
• The axons of the nerve cells within the geniculate body leave it to form the optic radiation
• Crossed fibers to 1., 4., 6. Uncrossed fibres to 2., 3., 5.

Dorsal pathway: “Magnocellular pathway” , Y

• (the ‘where’ functions)
• Parietal and frontal lobe:
• 10% of fibers
• 1,2 layers of GL
• To: V1 and FEF
  
  • Contrast, rough discrimination,
  • Black and white information.
  • Motion related information
  • Its fibres are thick and have high speed of information transfer.

Ventral pathway: Parvocellular pathway (X)

• (the ‘what’ functions)
• Temporal lobe
• 80% of fibers
• 3-5 layers of GL
• To: V1
  
  • Fine discrimination
  • Colour information and high contrast black and white information.
  • Its nerve fibres are thin and transfer information relatively slowly.

Other: Third type (W)

• Tectum
• 10%
• Collaterals

5-Optic Radiation, Gratioleti (geniculo-cortical tr)

• Axons of the nerve cells of the lateral geniculate body.
• Splits into 2 parts:
  
  • Lower loop (of Meyer Archambault)/ Anterior fasiculus
    
    • Passes though temporal lobe and loops around inf horn of lateral ventricle
    • through the white matter of the temporal lobe to access the inferior bank of the calcarine sulcus of the lingual gyrus.
    • Fibers from lower 1/2 of retina
    • Upper 1/2 of visual field (due to lens inversion)
  • Upper loop (of baum)/ Posterior fasiculus
    
    • Passes straight though parietal lobe into occupital lobe
    • superior bank of the calcarine sulcus of the cuneus, as they pass through the retrolenticular part of the internal capsule.
    • Upper 1/2 of retina
    • Lower 1/2 of visual field
• The tracts corresponding to the macula and fovea are referred to as the geniculostriate fibers and they arise from the center of the lateral geniculate nucleus to access the caudal visual cortex.

Collaterals: Branching off the visual pathway (all branches leave 3rd neuron), to:

• ​Autonomic reflex
  
  • Hypothalamus: suprachiasmatic and paraventricular ncl
  • Transmit information of intensity of daylight, which affects the release of hormones (melatonin)
• Coordination of visual and sensory inputs: Pulvinar TH
• Transfer of visual impulses to motor:
  
  • Superior colliculus
    
    • Is connected to the lateral geniculate body by the superior brachium.
    • It receives afferent fibers from the optic nerve, the visual cortex, and the spinotectal tract.
    • The efferent fibers form the tectospinal and tectobulbar tracts:
      
      • Probably responsible for the reflex movements of the eyes, head, and neck in response to visual stimuli.
  • *Tectal visual circle: Control of eye, head and neck muscles with towards visual impluses
• Pupillary reflexes
  
  • Brachium superior coliculus → superior colliculus → termination in pretectal ncl responsible for pupilary reflex

*Mydriasis: (dilation)

• …optic tract→ pretectal ncl → RF:
  
  • via tractus reticulospinalis -
• → centrum ciliospinale C8-Th1:
  
  • via sympathetic tract in the truncus symphaticus
• → superior cervical sympathetic ganglion → through the internal carotid plexus and ophtalmicus
• → Short ciliary nerves: m. dilatator pupillae

*Miosis (constriction​)

• …optic tract→ pretectal ncl → n. III (EW) (Nucleus accessorius dorsalis)
  
  • ​parasympathetic nuclei
• through third cranial nerve→ cillairy ggl→ nn. short cillary:
• to m. ciliaris and m. sphincter pupillae
• Direct light reflex:
  
  • The constriction of the pupil on which the light is shone
  • Consensual light reflex: constriction of the opposite pupil,
    
    • Even though no light fell on that eye
    • Because the pretectal nucleus sends fibers to the parasympathetic nuclei on both sides of the midbrain

*Convergence:

• → via area pretectalis → nucleus intersticialis /Cajal→ fasciculus longitudinalis medialis → nuclei of n. III., IV. and VI.
  
  • Ncl of extraocular muscles nerves

*Accommodation =When the eyes are directed from a distant to a near object

• The lens thickens to increase its refractive power by contraction of the ciliary muscle
• The pupils constrict to restrict the light waves to the thickest central part of the lens.
• Contraction of the medial recti brings about convergence of the ocular axes
• AF:
  
  • Optic nerve→ optic chiasma →optic tract →lateral geniculate body→ optic radiation→ visual cortex
• EF:
  
  • Vsual cortex → frontal eye field → descend through the internal capsule→ to the oculomotor nuclei in the midbrain→ to the medial recti muscles.
  • Some of the descending cortical fibers synapse with
    
    • → parasympathetic nuclei (Edinger-Westphal nuclei) of the third cranial nerve on both sides: Miosis (constriction​)
  • Same as miosis, but via ncl. interstitialis Cajali and not pretectal ncl​????
• Other: Corneal Reflex*
• Light touching of the cornea or conjunctiva results in blinking of the eyelids.
• Afferent impulses from the cornea or conjunctiva* → through the ophthalmic division of the trigeminal nerve → sensory nucleus of the trigeminal nerve → Internuncial neurons: medial longitudinal fasciculus→ motor nucleus of the facial nerve on both sides
• The facial nerve and its branches supply the orbicularis oculi muscle, which causes closure of the eyelids.*

Binocular Vision

• In binocular vision, the right and left fields of vision are projected on portions of both retinae
• The image of an object in the right field of vision is projected on:
  
  • the nasal half of the right retina
  • the temporal half of the left retina.
• In the optic chiasma,
  
  • the axons from these two retinal halves are combined to form the left optic tract.
• The lateral geniculate body neurons
  
  • now project the complete right field of vision on the visual cortex of the left hemisphere
  • and the left visual field on the visual cortex of the right hemisphere
• The lower retinal quadrants (=upper field of vision)
  
  • project on the lower wall of the calcarine sulcus,
• The upper retinal quadrants (=lower field of vision)
  
  • project on the upper wall of the sulcus.
• Note also that the macula lutea is represented on the posterior part of area 17, and the periphery of the retina is represented anteriorly.

Lesions of the Visual Pathway

Site of lesion

• Optic nerve – blindness
• Optic chiasma – bitemporal hemianopsia
• Partial lesion of the optic chiasma on its lateral side: Nasal Hemianopia
• Optical tract, lateral geniculate body – contralateral hemianopsia
• Meyers loop – contralateral quadrantanopsia
• V1 – contralateral hemianopsia with macular sparing

Occipital Lobe

Primary visual area (Brodmann area 17)

• Occupies the upper and lower lips of the calcarine sulcus on the medial surface of the cerebral hemisphere
  
  • (cuneus and lingual gyrus)
• Microscopically, it is seen to be a granular type of cortex with only a few pyramidal cells present.
• Controls involuntary pursuit and tracking eye movements
• AF: lateral geniculate body.
  
  • The fibers first pass forward in the white matter of the temporal lobe and then turn back to the primary visual cortex in the occipital lobe.
  • The visual cortex receives fibers from the temporal half of the ipsilateral retina and the nasal half of the contralateral retina.
  • The right half of the field of vision, therefore, is represented in the visual cortex of the left cerebral hemisphere and vice versa.
  • It is also important to note that the superior retinal quadrants (inferior field of vision) pass to the superior wall of the calcarine sulcus, while the inferior retinal quadrants (superior field of vision) pass to the inferior wall of the calcarine sulcus.
  • The macula lutea, which is the central area of the retina and the area for most perfect vision, is represented on the cortex in the posterior part of area 17 and accounts for one-third of the visual cortex.

The secondary visual area (Brodmann areas 18 and 19)

• Surrounds the primary visual area on the medial and lateral surfaces of the hemisphere
• This area receives afferent fibers from area 17 and other cortical areas as well as from the thalamus.
• Function:
• Relate the visual information received by the primary visual area to past visual experiences, thus enabling the individual to recognize and appreciate what he or she is seeing.

Occipital eye field

• Thought to exist in the secondary visual area
• Stimulation produces conjugate deviation of the eyes, especially to the opposite side.
• The involuntary following of moving objects by the eyes
• Connected by association fibers to the frontal eye field

Frontal eye field

• Extends forward from the facial area of the precentral gyrus into the middle frontal gyrus (parts of Brodmann areas 6, 8, and 9).
• Conjugate movements of the eyes, especially toward the opposite side.
• Thought to pass to the superior colliculus of the midbrain.
• The superior colliculus is connected to the nuclei of the extraocular muscles by the reticular formation.
• Control voluntary scanning movements of the eye and is independent of visual stimuli.

Visual association cortex

• Located in the angular gyrus
• Integrates visual sensory information for pattern recognition

Question 18

Olfactory and gustatory pathway, olfactory nerve

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353

Answer 18

Olfactory nerve, CN 1

General:

• Special somatic afferent nerve which innervates the olfactory mucosa within the nasal cavity.
• It carries information about smell to the brain.

Pathway:

• 2 neuron tract
• Does nto deccusate

Olfactory region

• Specilized olfactory epithlium on the roof of the nasal cavity and superior part of nasal spetum
• Cell types
  
  • The olfactory receptor cells, supporting cells, and basal (stem) cells.

Olfactory cells and nerve

• The olfactory receptor cells
  
  • Scattered among supporting cells.
  • Small bipolar nerve cell with a coarse peripheral process that passes to the surface of the membrane and a fine central process.
    
    • Coarse peripheral process:
      
      • Olfactory hairs (a number of short cilia arise) project into the mucus covering the surface of the mucous membrane.
      • React to odors in the air and stimulate the olfactory cells.
    • Fine central processes:
      
      • Form the olfactory nerve fibers
      • The olfactory nerve fibers are unmyelinated and are covered with Schwann cells.
      • Bundles of these nerve fibers pass through the openings of the cribriform plate of the ethmoid bone to enter the olfactory bulb. ​

Olfactory bulb

• Main relay station within the olfactory pathway.
• Ovoid structure
• Possesses several types of nerve cells:
  
  • Mitral cell
    
    • The incoming olfactory nerve fibers synapse with the dendrites of the mitral cells
    • Form rounded areas known as synaptic glomeruli.
      
      • Place where incoming receptor cell axons make connections with the dendrites of mitral relay neurons.
  • Tufted cells and granular cells
    
    • Smaller nerve cells,
    • Also synapse with the mitral cells.
  • Axons from the contralateral olfactory bulb through the olfactory tract.

Olfactory tract

• Narrow band of white matter
• Origin: From the posterior end of the olfactory bulb beneath the inferior surface of the frontal lobe of the brain
  
  • It consists of the central axons of the mitral and tufted cells of the bulb and some centrifugal fibers from the opposite olfactory bulb.
• At the anterior perforated substance→
  
  • Divides into medial and lateral olfactory striae.
  • The lateral stria
    
    • Primary olfactory cortex:
      
      • Periamygdaloid and Prepiriform areas
  • The medial olfactory stria
    
    • Carries the fibers that cross the median plane in the anterior commissure to pass to the olfactory bulb of the opposite side.

Additional

• Note that in contrast to all other sensory pathways,
  
  • the olfactory afferent pathway has only two neurons and reaches the cerebral cortex without synapsing in one of the thalamic nuclei.

Olfactory cortex output structures

• Secondary olfactory cortex:
  
  • Receives numerous connections from the primary olfactory cortex
  • The entorhinal area (area 28) of the parahippocampal gyrus
    
    • which is the anterior part of the parahippocampal gyrus, and is involved in the formation of memory.
  • Responsible for the appreciation of olfactory sensations
• Orbitofrontal cortex via the dorsal medial nucleus of the thalamus.
  
  • A part of prefrontal cortex, underside of the frontal lobe and situated over the eye orbit.
    
    • Lesions of this cortical region can result in an inability to distinguish different odors.
• Odor information is also sent to portions of the hypothalamus and brainstem
  
  • Trigger autonomic responses involved in appetite, salivation, and gastric contraction.

Clinical:

• Bilateral anosmia
  
  • Can be caused by disease of the olfactory mucous membrane, such as the common cold or allergic rhinitis.
• Unilateral anosmia
  
  • Can result from disease affecting the olfactory nerves, bulb, or tract.
• A lesion of the olfactory cortex on one side is unlikely to produce complete anosmia, because fibers from each olfactory tract travel to both cerebral hemispheres.
  
  • Fractures of the anterior cranial fossa involving the cribriform plate of the ethmoid could tear the olfactory nerves.
  • Cerebral tumors of the frontal lobes or meningiomas of the anterior cranial fossa can produce anosmia by pressing on the olfactory bulb or tract.

Gustatory pathway:

• 3 neuron tract
• Uncrossed
• Function: preception of taste
  
  • Information processes on the taste buds of the surface of the tounge, phrynx and palate

Neurons:

• 1st order neuron:
  
  • In ganglia of cranial nerves
  • N: VII, IX, X
• 2cd order neuron:
  
  • Ncl. of solitary tract
• 3rd order neuron
  
  • Vental posteromedial ncl of thalamus

Course of path:

1- Dendrite of 1st order neurons synapse with taste receptor cells

• Runs to ganglia of CN depending on location of taste bud
  
  • Ant. 2/3 of tounge → lingual n.→ Chorda tympani n. → geniculate ggl. → facial n.
    
    • Anterior to the sulcus terminalis)
  • Palate → palatine fibers→ n. of pterygoid canal→ Greater petrosal n. → geniculate gl. → facial n.
  • Post. 1/3 of tounge (including vallate papillae)→ sup. and inf. ggl of glossopharyngeal n. (in area of jugular foamen) → n. IX
  • Epiglottis, epiglottic valleculae→ sup. and inf. ggl of vagus n → n. X

2- ​​To ncl of solitary tract:

• Rostal part is termed gustatory ncl
• Collaterals to RF and limbic system
• Join central tegmental tract and run ipsilateral to TH

3- Interpolation in VPM of TH

4- Termination:

• Gustatory area BA 43,
  
  • Inf. part of the poscentral gyrus, parietal lobe
• Insular lobe
  
  • taste information has effect on the control centers of the digestive sysem motility and secratory activity
    *