2020-07-01
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Among them, stellate, pyramidal, spindle-shaped and horizontal cells are distinguished in shape. Pyramidal neurocytes have a triangular or pyramidal body shape, body diameter of 10-150 microns (small, medium, large and giant). The axon departing from the base of the pyramid cell is involved in the formation of descending pyramidal pathways, associative and commissural bundles, i.e. pyramidal cells are efferent cortical neurocytes. Long dendrites extend from the apex and lateral surfaces of the triangular body of the neurocytes. Dendrites have spines - places of synaptic contacts. One cell of such spines can have up to 4-6 thousand.
Stellate neurocytes are star-shaped; dendrites extend from the body in all directions, short and without spines. Stellate cells are the main sensory sensory elements of the cortex and their bulk is located in the 2nd and 4th layer of the cerebral cortex.
The cerebral cortical neurocytes are characterized by a regular layered arrangement, which forms the cytoarchitecture of the cortex.
There are 6 layers in the cortex:
1. Molecular layer (the most superficial) - consists mainly of tangential nerve fibers, there is a small number of fusiform associative neurocytes.
2. The external granular layer is a layer of small stellate cells. Their dendrites are in the molecular layer, part of the axons are directed to white matter, the other part of the axons rises to the molecular layer.
3. The pyramidal layer - consists of small and medium sized pyramidal cells. Axons go into white matter and in the form of associative bundles are sent to other convolutions of the hemisphere or in the form of commissural bundles in the opposite hemisphere.
4. The inner granular layer - consists of sensory stellate neurocytes having associative connections with neurocytes of the upper and lower layers.
5. Ganglionic layer - consists of giant pyramidal cells of BETs! The dendrite, which moves away from the top of the pyramidal neuron, rises into the molecular layer of the cortex. Dendrites extending from the lateral surface of these neurons remain within their layer! And the axon of the cell goes into white matter and forms descending projection pyramidal paths, also commissural bundles in the opposite hemisphere.
6. Layer of polymorphic cells - formed by neurocytes of the most various shapes (hence the name). Axons of neurocytes are involved in the formation of descending projection paths. Dendrites penetrate the entire thickness of the cortex and reach the molecular layer.
The structural and functional unit of the cerebral cortex is a module or column.
A module is a collection of neurocytes of all 6 layers located on one perpendicular space and closely interconnected with each other and subcortical formations.
In space, the module can be represented as a cylinder penetrating all 6 layers of the cortex, oriented with its long axis perpendicular to the surface of the cortex and having a diameter of about 300 microns. In the cerebral cortex of a person, there are about 3 million modules. Each module contains up to 2 thousand neurocytes. In addition to participating in the formation of projection pyramidal paths, each module establishes links with 2-3 modules of this and the opposite hemisphere.
White matter consists of the following nerve fibers that cause myeloarchitectonics of the cerebral cortex:
associative (connect the gyrus of one hemisphere),
commissural (connect the gyrus of the opposite hemispheres)
projection (connect the cortex to the underlying departments of the National Assembly)
The cerebral cortex also contains a powerful neuroglial apparatus that performs trophic, protective, and mechanical support functions. Glia contains all known elements - astrocytes, oligodendrogliocytes and brainmacrophages.
DORSAL ROOT GANGLION (sensory)
are located along the posterior roots of the spinal cord.
Outside, the dorsal root ganglion is covered with a connective tissue capsule; septa containing blood vessels extend from the capsule inward.
Under the capsule groups of neurocyte bodies are located.
The neurocytes are large, round in shape, the diameter of the bodies is up to 120 microns. The nuclei of the neurocytes are large, with clear nucleoli, located in the center of the cell.
The neurons of the spinal node are pseudo-unipolar in structure - the axon and dendrite depart from the body of the cell together as one process, then diverge in a T-shape. But in the process of embryogenesis, the neurons were laid as bipolar, and later the axon and dendrite merged together, forming a pseudo-unipolar neuron!
Dendrite goes to the periphery and forms in the skin, in the thickness of the tendons and muscles, in the internal organs sensitive receptor endings that perceive pain, temperature, tactile stimuli, i.e. Neurons of DR ganglion are sensitive in function. Axons along the back root enter the spinal cord and transmit impulses to the associative neurocytes of the spinal cord.
The bodies of neurocytes are surrounded by satellite cells or mantle cells - a type of oligodendrogliocyte.
In the central part of the spinal node, it consists of parallel processes of nerve cell processes coated with neurolemmocytes.
Autonomic nervous system (ANS)
innervates internal organs, blood vessels, glands and regulates the processes of blood circulation, respiration, digestion, metabolism, thermoregulation, etc., i.e. prepares and provides somatic effects with appropriate metabolic processes. The ANS is independent of consciousness, but this autonomy is relative, since all aspects of its activity are controlled by the cerebral cortex (a vivid example of this is fakirs, yogis who can control the work of internal organs).
