What are the ascending and descending tracts of the spinal cord. Particular histology nervous system
The spinal cord is located in the spinal canal and has the appearance of a rounded cord in cross section, expanded in the cervical and lumbar regions. It consists of two symmetrical halves, separated anteriorly by the median fissure, posteriorly by the median groove, and is characterized by a segmental structure. Each segment is associated with a pair of anterior (ventral) and a pair of posterior (dorsal) roots. The spinal cord consists of centrally located gray matter and surrounding white matter. The gray matter in the section has the shape of a butterfly. The projections of gray matter that run along the spinal cord are called columns. There are rear, side and front pillars. The pillars in cross section are called horns. Gray matter consists of groups of multipolar neurons and neurogliocytes, unmyelinated and thin myelinated fibers.
Clusters of neurons that share a common morphology and function are called nuclei . In the posterior horns there are:
· marginal Lissauer zone - the place of branching of the fibers of the dorsal roots when they enter the spinal cord;
· spongy substance , represented by a large-loop glial skeleton with large neurons;
· gelatinous (jelly-like) substances o, formed by neuroglia with small nerve cells;
· dorsal horn nucleus , consisting of tuft cells, the processes of which, passing through the anterior commissure into the lateral cord of the opposite side of the spinal cord, reach the cerebellum as part of the anterior spinocerebellar tract;
· Clarke core , also consisting of tuft cells, the axons of which, passing as part of the posterior spinocerebellar tract, are connected to the cerebellum.
The intermediate zone of gray matter surrounds the spinal canal, which is lined with ependymoglia. In the intermediate zone there are nuclei:
· medial, consisting of tuft cells, the neurons of which join the anterior spinocerebellar tract;
· lateral, located in the lateral horns, consisting of a group of association cells, which are the first neuron of the efferent sympathetic pathway.
The largest nerve cells lie in the anterior horns, as part of the posterior and anterior medial nuclei, formed by motor (root) neurons, the axons of which exit the spinal cord as part of the anterior roots and innervate the muscles of the trunk. The posterior and anterior lateral nuclei are also formed by motor neurons that innervate the muscles of the upper and lower extremities.
The white matter is represented by longitudinally running pulpy nerve fibers, collected in bundles, making up the conductive tracts of the spinal cord. The white matter is divided into: posterior, lateral and anterior cord.
The bundles are divided into two groups: some connect only separate sections of the spinal cord and lie in the anterior and lateral cords directly next to the gray matter, forming their own pathways of the spinal cord. Another group of bundles connects the spinal cord and brain.
There are ascending and descending paths. The ascending tracts form the posterior cord and ascend into the medulla oblongata.
Distinguish gentle Gaulle bun, formed by the axons of sensory cells, the receptors of which lie in the lower half of the body and wedge-shaped bundle of Burdach , the receptors of which perceive excitation in the upper half of the body. These bundles end in the nuclei of the medulla oblongata. These are the paths of tactile, pain, and temperature sensitivity.
The lateral cord consists of the ascending tracts of the spinocerebellar anterior and spinocerebellar posterior. Stimulation along these pathways reaches the anterior part of the cerebellum and switches to the motor pathways running from the cerebellum to the red nucleus.
Descending paths include:
1. Pathways connecting the spinal cord with the cerebral cortex: pyramidal, corticospinal way and anterior corticospinal path lying in the anterior funiculus. These pathways are of great importance for the implementation of conscious coordinated movements of the body. All motor impulses of these movements are transmitted through the pyramidal tracts. Bulbospinal the path also carries impulses from the cerebral cortex.
2. Communication with the medulla oblongata is carried out by vestibulospinal path (deuterospinal), which is of great importance for maintaining and correct orientation of the body in space, since to the cells of the nucleus Deiters the processes of neurons that have receptor apparatuses in the semicircles of the vestibular apparatus are suitable.
3. Connects with the cerebellum and midbrain rubrospinal tract coming from the cells of the red nuclei of the spinal cord. Impulses traveling along this path control all automatic movements.
4. No less important is the connection between the spinal cord and the quadrigeminal midbrain, which is carried out tectospinal And reticulospinal ways. The quadrigeminal region receives fibers from the optic nerve and from the occipital region of the cortex, and impulses traveling along this path to the motor neurons provide clarification and direction of movements.
The spinal cord consists of two symmetrical halves, delimited from each other in front by the deep median fissure, and behind by the median sulcus. The spinal cord is characterized by a segmental (metameric) structure (31-33 segments); each segment is associated with a pair of anterior (ventral) and a pair of posterior (dorsal) roots.
In the spinal cord there are gray matter, located in the central part, and white matter, lying on the periphery.
The outer boundary of the white matter of the spinal cord is formed by limiting glial membrane, consisting of fused flattened processes of astrocytes. This membrane is pierced by the nerve fibers that make up the anterior and posterior roots.
Throughout the entire spinal cord, in the center of the gray matter there passes the central canal of the spinal cord, which communicates with the ventricles of the brain.
Gray matter in cross section has the appearance of a butterfly and includes front, or ventral, rear, or dorsal, and lateral, or lateral, horns. The gray matter contains the bodies, dendrites and (partially) axons of neurons, as well as glial cells. The main component of gray matter, distinguishing it from white matter, are multipolar neurons. Between the cell bodies of neurons is neuropil- a network formed by nerve fibers and processes of glial cells.
Among all the neurons of the spinal cord, three types of cells can be distinguished:
radicular,
· internal,
· bundled.
Axons radicular cells leave the spinal cord as part of its anterior roots; these are cells of the lateral and anterior horns. Processes internal cells end with synapses within the gray matter of the spinal cord (mainly neurons of the dorsal horns). Axons tuft cells pass through the white matter in separate bundles of fibers that carry nerve impulses from certain nuclei of the spinal cord to its other segments or to the corresponding parts of the brain, forming pathways.
During the development of the spinal cord from the neural tube, neurons are isogenetically grouped into 10 layers, or Rexed plates. In this case, I-V plates correspond to the posterior horns, VI-VII plates - the intermediate zone, VIII-IX plates - the anterior horns, X plate - the zone near the central canal. On transverse sections, nuclear groups of neurons are more clearly visible, and on sagittal sections, the lamellar structure is better visible, where neurons are grouped into Rexed columns.
Cells similar in size, structure and functional significance lie in the gray matter in groups called cores.
IN hind horns distinguish the spongy layer, gelatinous substance, nucleus of the dorsal horn and Clark's thoracic nucleus, Roland's nucleus with inhibitory neurons, Lissauer's area.
Neurons spongy zone and gelatinous substance They communicate between the sensory cells of the spinal ganglia and the motor cells of the anterior horns, closing local reflex arcs.
Neurons Clarke kernels receive information from receptors of muscles, tendons and joints (proprioceptive sensitivity) along the thickest radicular fibers and transmit it to the cerebellum; these are large multipolar neurons.
Neurons own core dorsal horn are intercalary small multipolar cells, the axons of which end within the gray matter of the spinal cord on the same side (associative cells) or the opposite side (commissural cells).
Between the posterior and lateral horns, the gray matter protrudes into the white matter in strands, as a result of which its network-like loosening is formed, called the reticular formation, or the reticular formation of the spinal cord.
In the intermediate zone (lateral horns) the centers of the autonomic (autonomic) nervous system are located - preganglionic cholinergic neurons of its sympathetic and parasympathetic divisions.
IN front horns The largest neurons of the spinal cord are located. These are radicular cells because their axons make up the bulk of the fibers of the anterior roots. In the anterior horns there are 3 types of neurons, forming 5 groups of nuclei that are significant in volume (lateral - the anterior and posterior group, medial - the anterior and posterior group and the central or intermediate nucleus).
Alpha motor neurons- large neurons 100-140 microns. By function, they are motor and their axons, as part of the anterior roots, exit the spinal cord and are directed to the striated muscles.
Gamma motor neurons– smaller ones, are cells that control the force and speed of contraction.
Renshaw cells - inhibitory cells carry out mutual inhibition of flexor and extensor motor neurons, and also carry out reciprocal inhibition.
White matter The horns of the brain are divided into columns: anterior (descending), middle (mixed) and posterior (ascending). The white matter of the spinal cord is a collection of longitudinally oriented predominantly myelinated nerve fibers. The bundles of nerve fibers that communicate between different parts of the nervous system are called tracts, or pathways, of the spinal cord.
4. Reflex apparatus of the spinal cord (somatic reflex arcs)
The elementary reflex arc of the spinal cord's own apparatus is represented by two neurons. The body of the first afferent neuron located in the spinal ganglion. Its dendrite is directed to the periphery and ends with a receptor. The axon of an afferent neuron as part of the dorsal roots enters the spinal cord, its dorsal horns, and transits to the cells of the anterior horns of the spinal cord. The anterior horns contain bodies motor efferent cells– large alpha motor neurons, on which the axon of the sensitive cell ends with an axosomatic synapse. The axon of the efferent neuron leaves the spinal cord, enters the ventral roots, then enters the spinal nerve, plexus, and finally reaches the somatic nerve. effector organ(muscles, glands).
When irritation is applied (prick of a finger), the receptor apparatus (skin noceceptors) is irritated and a nerve impulse is generated, which is carried centripetally through the dendrite, the body of the afferent neuron and its axon through a synaptic connection to the body of the second efferent neuron. From there, the nerve impulse centrifugally leaves the spinal cord, anterior root, and nerve through the cell axon and causes excitation in the effector organ (biceps brachii muscle), which, in turn, leads to the expected effect - withdrawal of the hand.
The principle of the structure and operation of vegetative reflex arcs is understood independently.
Represents flattened cord, located in the spinal canal, about 45 cm long in men and 42 cm in women. At the points where the nerves exit to the upper and lower extremities, the spinal cord has two thickenings: cervical and lumbar.
The spinal cord consists of two types of fabric: outer white matter (bundles of nerve fibers) and inner gray matter (nerve cell bodies, dendrites and synapses). In the center of the gray matter, a narrow canal containing cerebrospinal fluid runs along the entire brain. The spinal cord has segmental structure(31-33 segments), each section is associated with a specific part of the body, 31 pairs of spinal cords depart from the segments of the spinal cord nerves: 8 pairs of cervical (Ci-Cviii), 12 pairs of thoracic (Thi-Thxii), 5 pairs of lumbar (Li-Lv), 5 pairs of sacral (Si-Sv) and a pair of coccygeal (Coi-Coiii).
Each nerve as it leaves the brain is divided into anterior and posterior roots. Posterior roots– afferent pathways, anterior roots efferent pathways. Afferent impulses from the skin, motor system, and internal organs enter the spinal cord along the dorsal roots of the spinal nerves. The anterior roots are formed by motor nerve fibers and transmit efferent impulses to the working organs. Sensory nerves predominate over motor nerves, therefore, a primary analysis of incoming afferent signals occurs and the formation of reactions that are most important for the body at the moment (transmission of numerous afferent impulses to a limited number of efferent neurons is called convergence).
Total quantity spinal cord neurons is about 13 million. They are divided: 1) according to the department of the nervous system - neurons of the somatic and autonomic nervous system; 2) by purpose – efferent, afferent, intercalary; 3) by influence - exciting and inhibitory.
Functions of spinal cord neurons.
Efferent neurons belong to the somatic nervous system and innervate skeletal muscles - motor neurons. There are alpha and gamma motor neurons. A motor neurons transmit signals from the spinal cord to skeletal muscles. The axons of each motor neuron divide multiple times, so each of them spans many muscle fibers, forming a motor motor unit. G motor neurons innervate the muscle fibers of the muscle spindle. They have a high impulse frequency and receive information about the state of the muscle spindle through intermediate neurons (interneurons). Generate pulses with a frequency of up to 1000 per second. These are phonoactive neurons with up to 500 synapses on their dendrites.
Afferent neurons somatic NS are localized in the spinal ganglia and ganglia of the cranial nerves. Their processes carry out impulses from muscle, tendon, and skin receptors, enter the corresponding segments of the spinal cord and connect by synapses with intercalary or alpha motor neurons.
Function interneurons consists of organizing connections between the structures of the spinal cord.
Neurons of the autonomic nervous system are intercalary . Sympathetic neurons located in the lateral horns of the thoracic spinal cord, they have a rare impulse frequency. Some of them are involved in maintaining vascular tone, others in the regulation of the smooth muscles of the digestive system.
A collection of neurons forms nerve centers.
The spinal cord contains regulatory centers most internal organs and skeletal muscles. Centers skeletal muscle control are located in all parts of the spinal cord and innervate, according to a segmental principle, the skeletal muscles of the neck (Ci-Civ), diaphragm (Ciii-Cv), upper extremities (Cv-Thii), trunk (Thiii-Li), lower extremities (Lii-Sv). When certain segments of the spinal cord or its pathways are damaged, specific motor and sensory disorders develop.
Functions of the spinal cord:
A) provides two-way communication between the spinal nerves and the brain - conduction function;
B) carries out complex motor and autonomic reflexes - reflex function.
The spinal cord is characterized by a pronounced segmental structure, reflecting the segmental structure of the body of vertebrates. Two pairs of ventral and dorsal roots arise from each spinal segment. The dorsal roots form the afferent inputs of the spinal cord. They are formed by the central processes of the fibers of primary afferent neurons, the bodies of which are brought to the periphery and are located in the spinal ganglia. The ventral roots form the efferent exits of the spinal cord. The axons of a and g motor neurons, as well as preganglionic neurons of the autonomic nervous system, pass through them. This distribution of afferent and efferent fibers was established at the beginning of the last century and was called the Bell-Magendie law. After cutting the anterior roots on one side, a complete shutdown of motor reactions is observed; but the sensitivity of this side of the body remains. Transection of the dorsal roots turns off sensitivity, but does not lead to loss of motor reactions of the muscles.
1 - white matter;
2 - gray matter;
3 - posterior (sensitive) root;
4 - spinal nerves;
5 - anterior (motor) root;
6 - spinal ganglion
Neurons of the spinal ganglia belong to simple unipolar, or pseudounipolar, neurons. The name “pseudounipolar” is explained by the fact that in the embryonic period the primary afferent neurons arise from bipolar cells, the processes of which then merge. Neurons of the spinal ganglia can be divided into small and large cells. The body of large neurons has a diameter of about 60–120 μm, while in small neurons it ranges from 14 to 30 μm.
Large neurons give rise to thick myelinated fibers. Both thin myelinated and unmyelinated fibers begin from small ones. After bifurcation, both processes are directed in opposite directions: the central one enters the dorsal root and, as part of it, into the spinal cord, the peripheral one into various somatic and visceral nerves, approaching the receptor formations of the skin, muscles and internal organs.
Sometimes the central processes of primary afferent neurons enter the ventral root. This occurs when the axon of the primary afferent neuron trifurcates, as a result of which its processes are projected into the spinal cord and through the dorsal and ventral roots.
Of the entire population of dorsal ganglion cells, approximately 60–70% are small neurons. This corresponds to the fact that the number of unmyelinated fibers in the dorsal root exceeds the number of myelinated fibers.
The cell bodies of dorsal ganglia neurons do not have dendritic processes and do not receive synaptic inputs. Their excitation occurs as a result of the arrival of an action potential along the peripheral process in contact with the receptors.
Cells of the dorsal ganglia contain high concentrations of glutamic acid, one of the putative mediators. Their surface membrane contains receptors specifically sensitive to g-aminobutyric acid, which coincides with the high sensitivity to g-aminobutyric acid of the central endings of primary afferent fibers. Small ganglion neurons contain substance P or somatostatin. Both of these polypeptides are also likely transmitters released from the terminals of primary afferent fibers.
Each pair of roots corresponds to one of the vertebrae and leaves the spinal canal through the foramen between them. Therefore, segments of the spinal cord are usually designated by the vertebra near which the corresponding roots emerge from the spinal cord. The spinal cord is also usually divided into several sections: cervical, thoracic, lumbar and sacral, each of which contains several segments. In connection with the development of the limbs, the neural apparatus of those segments of the spinal cord that innervate them has received the greatest development. This was reflected in the formation of cervical and lumbar thickenings. In the area of thickening of the spinal cord, the roots contain the greatest number of fibers and have the greatest thickness.
On a cross section of the spinal cord, the centrally located gray matter, formed by a cluster of nerve cells, and the surrounding white matter, formed by nerve fibers, are clearly visible. In the gray matter, there are ventral and dorsal horns, between which lies an intermediate zone. In addition, in the thoracic segments there are also lateral protrusions of gray matter - the lateral horns.
All neural elements of the spinal cord can be divided into 4 main groups: efferent neurons, interneurons, neurons of the ascending tracts and intraspinal fibers of sensory afferent neurons. Motor neurons are concentrated in the anterior horns, where they form specific nuclei, all of whose cells send their axons to a specific muscle. Each motor nucleus usually extends into several segments. Therefore, the axons of motor neurons innervating the same muscle leave the spinal cord as part of several ventral roots.
In addition to the motor nuclei located in the ventral horns, large accumulations of nerve cells are distinguished in the intermediate zone of the gray matter. This is the main nucleus of interneurons of the spinal cord. The axons of interneurons extend both within a segment and into the nearest neighboring segments.
A characteristic cluster of nerve cells also occupies the dorsal part of the dorsal horn. These cells form dense weaves, and this zone is called the gelatinous substance of Roland.
The most accurate and systematic idea of the topography of the nerve cells of the gray matter of the spinal cord is provided by dividing it into successive layers, or plates, in each of which mainly neurons of the same type are grouped.
Although the layered typography of gray matter was originally identified in the spinal cord of the cat, it has proven to be quite universal and is quite applicable to the spinal cord of both other vertebrates and humans.
According to these data, all gray matter can be divided into 10 plates. The very first dorsal plate contains mainly so-called marginal neurons. Their axons project rostrally, giving rise to the spinothalamic tract. The fibers of the Lissauer tract, which is formed by a mixture of primary afferent fibers and axons of propriospinal neurons, end on the marginal neurons.
The second and third plates form a gelatinous substance. Two main types of neurons are localized here: smaller and relatively larger neurons. Although the cell bodies of neurons in the second lamina are small in diameter, their dendritic arborizations are quite numerous. The axons of neurons in the second plate project to the Lissauer tract and the dorsolateral fasciculus propria of the spinal cord, but many remain within the substantia gelatinosa. On the cells of the second and third plates, the fibers of primary afferent neurons, mainly skin and pain sensitivity, end.
The fourth plate occupies approximately the center of the dorsal horn. The dendrites of layer IV neurons penetrate the substantia gelatinosa, and their axons project to the thalamus and lateral cervical nucleus. They receive synaptic inputs from neurons of the substantia gelatinosa, and their axons project to the thalamus and lateral cervical nucleus. They receive synaptic inputs from neurons of the substantia gelatinosa and primary afferent neurons.
In general, the nerve cells of the first to fourth laminae occupy the entire apex of the dorsal horn and form the primary sensory area of the spinal cord. The fibers of most of the dorsal root afferents from exteroceptors, including skin and pain sensitivity, are projected here. In the same zone, nerve cells are localized, giving rise to several ascending tracts.
The fifth and sixth laminae contain numerous types of interneurons that receive synaptic inputs from dorsal root fibers and descending pathways, especially the corticospinal and rubrospinal tracts.
Propriospinal interneurons are localized in the seventh and eighth plates, giving rise to long axons that reach neurons in distant segments. Afferent fibers from proprioceptors, fibers of the vestibulospinal and reticulospinal tracts, and axons of propriospinal neurons end here.
The ninth plate contains the bodies of a- and g-motoneurons. This area is also reached by the presynaptic endings of primary afferent fibers from muscle stretch receptors, the endings of fibers of the descending tracts, corticospinal fibers, and the axon terminals of excitatory and inhibitory interneurons.
The tenth plate surrounds the spinal canal and contains, along with neurons, a significant number of glial cells and commissural fibers.
Neuroglial cells of the spinal cord cover the surface of neurons for a considerable extent, and the processes of the glial cell are directed, on the one hand, to the bodies of neurons, and on the other, often contact with blood capillaries, acting as intermediaries between nerve elements and their sources of nutrition.
The spinal cord transmits signals through the ascending pathways to the suprasegmental levels of the brain, and through the descending pathways it receives commands for action from there. The ascending pathways transmit impulses from proprioceptors along the fibers of the spinobulbar fascicles of Gaulle and Burdach and the spinocerebellar tracts of Govers and Flexigo, from pain and temperature receptors along the lateral spinothalamic tract, from tactile receptors along the ventral spinothalamic tract and partially along the fascicles of Gaulle and Burdach.
The descending tracts are composed of corticospinal, or pyramidal, tracts and extracorticospinal, or extrapyramidal.
The cerebellum is the central organ of balance and coordination of movements. It is formed by two hemispheres with a large number of grooves and convolutions, and a narrow middle part - the vermis.
The bulk of the gray matter in the cerebellum is located on the surface and forms its cortex. A smaller portion of the gray matter lies deep in the white matter in the form of the central nuclei of the cerebellum.
There are 3 layers in the cerebellar cortex: 1) the outer molecular layer contains relatively few cells, but many fibers. It distinguishes between basket and stellate neurons, which are inhibitory. Stellate - inhibit vertically, basket - send axons over long distances, which end on the bodies of pyriform cells. 2) The middle ganglion layer is formed by one row of large pyriform cells, first described by the Czech scientist Jan Purkinje. The cells have a large body, 2-3 short dendrites extend from the apex, which branch in a small layer. 1 axon extends from the base, which goes into the white matter to the cerebellar nuclei. 3) The inner granular layer is characterized by a large number of densely lying cells. Among the neurons, granule cells, Golgi cells (stellate), and fusiform horizontal neurons are distinguished. Granule cells are small cells that have short dendrites, the latter form excitatory synapses with mossy fibers in the cerebellar glamelura. Granule cells excite mossy fibers, and axons go into the molecular layer and transmit information to piriform cells and all the fibers located there. It is the only excitatory neuron in the cerebellar cortex. Golgi cells lie under the bodies of piriform neurons, axons extend into the glameruli of the cerebellum, and can inhibit impulses from mossy fibers to granule cells.
Afferent pathways enter the cerebellar cortex through 2 types of fibers: 1) liana-shaped (climbing) - they rise from the white matter through the granular and ganglion layers. They reach the molecular layer, form synapses with the dendrites of piriform cells and excite them. 2) Bryophytes - from the white matter enter the granular layer. Here they form synapses with the dendrites of granular cells, and the axons of granular cells go into the molecular layer, forming synapses with the dendrites of piriform neurons, which form inhibitory nuclei.
Cerebral cortex. Development, neural composition and layer-by-layer organization. The concept of cyto- and myeloarchitecture. Blood-brain barrier. Structural and functional unit of the cortex.
The cerebral cortex is the highest and most complexly organized nerve center of the screen type, the activity of which ensures the regulation of various body functions and complex forms of behavior. The cortex is formed by a layer of gray matter. Gray matter contains nerve cells, nerve fibers and neuroglial cells.
Among the multipolar neurons of the cortex, pyramidal, stellate, fusiform, arachnid, horizontal, “candelabra” cells, cells with a double bouquet of dendrites and some other types of neurons are distinguished.
Pyramidal neurons constitute the main and most specific form for the cerebral cortex. They have an elongated cone-shaped body, the apex of which faces the surface of the cortex. Dendrites extend from the apex and lateral surfaces of the body. Axons originate from the base of the pyramidal cells.
Pyramidal cells of different layers of the cortex differ in size and have different functional significance. Small cells are interneurons. Axons of large pyramids take part in the formation of motor pyramidal tracts.
The neurons of the cortex are located in vaguely delimited layers, which are designated by Roman numerals and numbered from the outside to the inside. Each layer is characterized by the predominance of one type of cell. There are six main layers in the cerebral cortex:
I - The molecular layer of the cortex contains a small number of small associative horizontal cells of Cajal. Their axons run parallel to the surface of the brain as part of the tangential plexus of nerve fibers of the molecular layer. However, the bulk of the fibers of this plexus are represented by the branching of dendrites of the underlying layers.
II - The outer granular layer is formed by numerous small pyramidal and stellate neurons. The dendrites of these cells rise into the molecular layer, and the axons either go into the white matter or, forming arcs, also enter the tangential plexus of fibers of the molecular layer.
III - The widest layer of the cerebral cortex is the pyramidal layer. It contains pyramidal neurons and spindle cells. The apical dendrites of the pyramids extend into the molecular layer, and the lateral dendrites form synapses with adjacent cells of this layer. The axon of a pyramidal cell always extends from its base. In small cells it remains within the cortex, in large cells it forms a myelin fiber that goes into the white matter of the brain. Axons of small polygonal cells are directed into the molecular layer. The pyramidal layer performs primarily associative functions.
IV - The internal granular layer is very well developed in some cortical fields (for example, in the visual and auditory areas of the cortex), while in others it may be almost absent (for example, in the precentral gyrus). This layer is formed by small stellate neurons. It contains a large number of horizontal fibers.
V - The ganglion layer of the cortex is formed by large pyramids, and the area of the motor cortex (precentral gyrus) contains giant pyramids, which were first described by the Kiev anatomist V. A. Betz. The apical dendrites of the pyramids reach the first layer. The axons of the pyramids project to the motor nuclei of the brain and spinal cord. The longest axons of Betz cells in the pyramidal tracts reach the caudal segments of the spinal cord.
VI - The layer of polymorphic cells is formed by neurons of various shapes (fusiform, stellate). The axons of these cells extend into the white matter as part of the efferent pathways, and the dendrites reach the molecular layer.
Cytoarchitecture – features of the location of neurons in different parts of the cerebral cortex.
Among the nerve fibers of the cerebral cortex, one can distinguish association fibers that connect individual parts of the cortex of one hemisphere, commissural fibers that connect the cortex of different hemispheres, and projection fibers, both afferent and efferent, that connect the cortex with the nuclei of the lower parts of the central nervous system.
Autonomic nervous system. General structural characteristics and main functions. The structure of sympathetic and parasympathetic reflex arcs. Differences between autonomic reflex arcs and somatic ones.
