THE HISTOPHYSIOLOGY OF THE BRAIN AND CEREBELLUM

Plan of the lecture. 1. Brain. The main principles of the brain steam and cortex organization. 2. Nuclear centers of the brain steam. 3. Cortex. 4. Cyto- and myeloarchitechtonics. 5. Morphofunctional unit. 6. Cerebellar cortex. 7. The morphofunctional features of the cerebellar neurons and interneuron relationships.

DEVELOPMENT OF THE NEURAL TUBE

DEVELOPMENT Anterior part of the nerve tube constrictions 3 vesicles division 5 vesicles (my-, met-, curvatures mes-, di-, telencephalon)

BRAIN STEAM MANTIA (CORTEX) myelencephalon diencephalon metncephalon mesencephalon The gray matter - numerous NUCLEI sensory associative motor

The types of the nerve centers 1. Nuclear (the nucleus is the number of neurons. NB! Similar structure and functions). Macro- (caudate, red, s. nigra, dentate) and micro- (cranial nerves, hypothalamic). 2. Projecting centres.

NB! Evolution of the analyzers. Rising of the neuron number. Extensive and intensive variants.

White matter of the brain steam. Comissural Projecting Associative Short Ascending Long descending

Reticular formation. Neurons: multipolar, grouped and the numerous nuclei. Organization: diffuse meshwork at the caudal parts of the brain steam, more compact - cranially. Relationships – ascending (activating the cortex), descending (oppressing motoneurons of the spinal cord). Neurotransmitters: Ach, NA, SER, DOPamine. Functions:

Cortex 1. 2. 3. 4. Projecting center Square – 1500 – 2500 sm 2 Thickness – 3 -5 mm 30%- external surface, 70% - inside the fissures 5. 10 -15 billions of neurons and more then 100 billlions of gliocytes Myeloarchitechtonics Cytoarchitechtonics– 52 fields

21 weeks 30 weeks 24 weeks 26 weeks 28 weeks 34 weeks 40 weeks

Molecular layer External granular Pyramidal Internal granular Ganglionic Polymorph layer Tangentional fibers Bechterev strip Radial fibers External strip (Bajarge) Internal strip (Bajarge)

By the shape and the placement: Ø pyramidal (up to 50%) – small, middle, big and large or giant (so called Betz cells). ; Ø stellate; Ø Horizontal Cajal cells (fusiform and horizontal pericaryons); Ø Martinotti cells; Ø Fusiform (polar dendrites).

horizontal neroglioform stellate pyramidal basket Martinotti fusiform 1. Molecular layer: small stellate, mainly – horizontal neurons. 2. External granular: stellate, small pyramidal. 3. Pyramidal layer: small (external part) and middle in size (internal part) pyramidal, stellate. 4. Internal granular: stellate neurons 5. Ganglionar layer: middle in size, big and large (giant) pyramidal neurons. 6. Polymorph layer: stellate, fusiform and pyramid neurons. NB! Martinitti cells are at each lauer excluding molecular one.

The types of the cortex Granular – sensory part. The 2 and 4 layers are most developed. Agranular – motor part. The 3, 5 and 6 layers are most developed. The main source of the efferent tracts.

Vertical columns 300 mkm in diameter. Each one consists of 4 -5 thousands neurons (approximately 2 -2. 5 thousands – pyramidal). There are 3. 000 modules at the cortex. Each one well related with the 10 and more other modules. As the morphofunctional unit the module has got al components of the reflex arch (afferent entrance, associative neurons, efferent exit). Afferent entrance – specific thalamocortical fibers, bringing specific impulses; integrative fibers (cortico-cortical: associative or comissural (corpus callosum, cerebral comissures)), which are axons of small or middle pyramidal neurons. Efferent exit – descending tracts: axons of giant and big pyramidal neurons. Module

Module The system of the local relationships – intermediate neurons (17 types). Most important: Axo-axonal cells – 2 -3 layers. Axons are orientated horizontally and form oppressing synapses at axons of pyramidal neurons at the same layers (Bechterev strip ). Fusiform neurons.

Module Basket cells – 2, 3, 4 and 5 layers. Horizontal axons end at the perykarions of 2030 pyramidal neurons. Oppress motoneurons at the volume of the 1 column – this is why they were called as “columnar” basket cells. Fusiform neurons - perykarions are at the 2 and 3 layers. Dendrites lead up and down. Axons and axonal collaterals form synapses at pyramidal and nonpyramidal (oppressors) neurons. This is why dual function. Stellate cells of the 2 -nd layer – their axons at the 1 -st layer contact with dendrites of pyramidal neurons and horizontal branches of cortico-cortical fibers.

Cerebellum Functions Anatomy Placement Grey matter (cortex and nuclei) White matter

Cerebellar cortex Molecular, ganglionar, granular layers

Molecular layer: Stellate cells – at the superficial part; small, too many processuses. Basket cells – at the lower third of the layer, more big; axons are parallel to the cortex, send collaterals forming baskets at the Purkinje cells.

Ganglionar layer: Purkinje cells. Big, oval perykarions, dendrites leading to the molecular layer where contact with the axons of the granular cells and afferent climbing fibers; perykarions are covered by axons of the basket cells; axons enter cerebellar nuclei.

Granular layer: Granule cells – most numerous and small; their axons enter molecular layer, where divide themselves (T-shaped division), then leading parallaly and contact with the dendrites of all other cells. Big stellate cells (Golgi). Horizontal cells (fusiform).

Main reflex arches at the cerebellar cortex In between cerebellar neurons there are strong determined relationships. There are 2 types of the impulse conduction and 3 types of it’s correction. The shortest reflex arch Climbing fibers Purkinje cells Cerebellar nuclei Climbing fibers – one of 2 types of the afferent fibers, coming from the spinal cord and vestibular nuclei. At the molecular layer they contact with the dendrites of Purkinje cells, activating them. Purkinje cell’s axons lead to the cerebellar nuclei and oppress them. Result: limiting of the cerebellar nuclei activity (stimulating the spinal cord’s motoneurons).

+ Climbing fibers

Long reflex arch Mossy fibers Granular cells Mossy fibers (afferent) coming from the olivary and pontinal nuclei (middle and lower cerebellar peduncules) and contact with the granule cell’s dendrites (at the granular layer); these synaptic contacts look like light varicosities. T-divided axons of the granule cells contact with the dendrites at the molecular layer. Activate Purkinje cells, which oppress cerebellar nuclei. Purkinje Cells Cerebellar nuclei

+ - +

Correction of the input signal at the cerebellar cortex Correction - limiting of the input signal Mossy fibers Granular cells Golgi cells Granule cells form synaptic contacts with the Golgi cells dendrites, activating them. Golgi cell’s axons produce synapses at the synaptic varicosities of the granular layer and oppress the neurotransmission here. Result: limited amplitude of the incoming impulse (from mossy fibers).

+ Golgi cell Granular cell + Mossy fibers

Correction of the input signal at the cerebellar cortex Purkinje cells Granular cells Cerebellar nuclei Stellate cells Basket cells Granule cells activate the basket cells and stellate one as well (not only the Purkinje and Golgi cells) forming synaptic contacts at their dendrites. Basket cell’s and stellate cell’s axons contact with the Purkinje cell’s, oppressing them. Result: oppressing oppression, rise the activity of the cerebellar nuclei.

Cerebellar cortex Cerebral cortex Purkinje cells. Pyramidal neurons – analogues of Purkinje neurons (main efferent cells as well). Differences: there are concentrated at one layer (diffused); axons lead to the spinal cord or other areas of the cortex (not to the subcortical nuclei); Axons form activating synapses (not oppressing) Granule cells Stellate neurons – analogues of granule neurons (they activate efferent cells also). Like at the cerebellum, the impulse from the afferent fiber can be transmitted to the pyramidal neuron directly or through the stellate cell. Basket and stellate cells Basket cells and axo-axonal neurons – analogues of basket and stellate cerebellar cells. They form oppressing synapses at the bodies and axons of pyramidal neurons and produce correction of the efferent response.

similarities differences As the result of the numerous similarities in between cells of the cerebellum and cerebral cortex, the functioning of the last one not too differ of the cerebellum. Like the cerebellar cortex, the cerebral cortex realize the recognition of the incoming information, it’s analysis and creation of efferent response. The last one can be corrected by the numerous accessory neurons. An analysis happens at the much more square of the cortex, because numerous small pyramidal cell relate by their horizontal processuses different zones of the cortex.