In the cortex, there are up to 15 and more billion neurocytes, some authors allow up to 50 billion.

NERVOUS SYSTEM

Assoc.prof. Kharchenko S.V.
Department of Histology and Embryology
|Medical Academy. S.I. Georgievsky

NERVOUS SYSTEM CONSISTS OF TWO DEPARTMENTS:

- CENTRAL NERVOUS SYSTEM (brain and spinal cord)

- PERIPHERAL NERVOUS SYSTEM (ganglia, peripheral nerves)

 

The brain and spinal cord are composed of gray and white matter.

The main difference between them: gray matter is formed by bodies of neurons, nerve fibers and glia, and white - only by nerve fibers and glia!

The spinal cord (SM) consists of 2 symmetrical halves, separated in front by a deep fissure, and behind by a commissure.

On the cross section, gray and white matter is clearly visible. The gray matter in the section has the shape of a butterfly or the letter "H" and has horns - posterior, lateral and anterior horns.

The abundance of neurocytes determines the gray color of the gray matter. According to morphology, neurocytes of spinal cord are multipolar. The neurocytes in the gray matter are surrounded by nerve fibers tangled up like felt. Axons in nerve fibers are weakly myelinated, and dendrites are not myelinated at all. Similar in size, fine structure and function neurocytes are arranged in groups and form nuclei.

Among the neurocytes of spinal cord the following types are distinguished:

1. Radicular neurocytes - are located in the nuclei of the anterior horns, are motor in function; axons of radicular neurocytes in the structure of the anterior roots leave the SM, conduct motor impulses to the skeletal muscle.

2. Internal cells — the processes of these cells do not leave the gray matter; they terminate within a given segment or an adjacent segment, that is, by function

3. Cells of bundles- the processes of these cells form nerve bundles of white matter and are sent to neighboring segments or overlying sections of the NS, ie by function are also associative.

 

The posterior horns of spinal cord are shorter, narrower and contain the following types of neurocytes:

a) bundle neurocytes - are diffusely located, receive sensitive impulses from the neurocytes of the spinal ganglia and pass along the ascending paths of white matter to the overlying sections of the NS (in the cerebellum, in the cerebral cortex);

b) internal neurocytes - transmit sensitive impulses from the spinal ganglia to the motor neurocytes of the anterior horns and to neighboring segments.

There are 4 structures in the posterior horns of Spinal cord:

1. Spongy substance - consists of small bundle neurocytes and gliocytes.

2. Substancia Gelatinousa - contains a large number of gliocytes, almost no neurocytes.

3. Nucleus proper - consists of bundle neurocytes that transmit impulses to the cerebellum and optic tubercle.

4. Clark's nucleus (Thoracicus nucleus) - consists of bundle neurocytes, the axons of which as part of the lateral cords are sent to the cerebellum.

In the lateral horns (intermediate zone) there are 2 medial intermediate nuclei and a lateral nucleus. Axons of bundle associative neurocytes of the medial intermediate nuclei transmit impulses to the cerebellum. The lateral nucleus of the lateral horns in the thoracic and lumbar spine is the central nucleus of the sympathetic part of the autonomic NS. The axons of the neurocytes of these nuclei go as part of the anterior roots of the spinal cord as preganglionic fibers and end on the neurocytes of the sympathetic trunk (prevertebral and paravertebral sympathetic ganglia). The lateral nucleus in the sacral section of the spinal cord is the central nucleus of the parasympathetic division of the autonomic NS.

Anterior horns contain a large number of motor neurons (motor neurons), forming 2 groups of nuclei:

1. The medial group of nuclei innervates the muscles of the body.

2. The lateral group of nuclei is well expressed in the cervical and lumbar thickening - innervates the muscles of the limbs.

Axons of motor neurons exit the spinal cord in the structure of the anterior roots, reach the skeletal muscles, end on each muscle fiber with a motor plaque.

The white matter of spinal cord consists of longitudinally oriented mainly myelin nerve fibers that form the posterior (ascending), anterior (descending) and lateral (and ascending and descending) cords, as well as glial elements.

The cerebellum is the central organ of balance and coordination of movements.

There are gray and white matter of the cerebellum.

The gray matter is located on the surface of the organ and is represented by the cerebellar cortex and the cerebellar nuclei, which are located in the white matter.

There are 3 layers in the cerebellar cortex:

1. External, molecular, layer - consists of basket -like and star -shaped neurocytes, which are associative in function.

The dendrites of these neurons remain within their layer! And axons go down into the ganglion layer and here they fit in the bodies of Purkinje cells, braid them and form baskets of nerve fibers!

Neurons of this layer inhibit Purkinje cells!

2. The middle, ganglionic layer - consists of 1 row of Purkinje flask-shaped cells (just take off the cerebellum's function of coordinating movement and balance)! These are rather large cells - body diameter up to 60 microns. Dendrites rise into the molecular layer and branch out strongly, are located in the 1st plane, and the axons go into the white matter and form the efferent (outgoing) pathways of the cerebellum and, after switching in the nuclei of the cerebellum, send impulses through the rubrospinal pathway to the spinal cord motor neurons.

3. The inner, granular layer - consists of granuk cells, large stellate neurocytes, spindle-shaped horizontal neurocytes (all cells are associative in function).

Granuk cells are small neurons! Their dendrites branch out in the form of a paw of a bird (there are 3-4 of them in quantity) and form synapses with mossy fibers - these structures are called glomeruli of the cerebellum!

The axons of these cells rise into the molecular layer and there branches T-shaped and runs parallel to the surface of the gray matter! In this case, the axon forms a synapse with the dendrite of the Purkinje cell, thus transmitting excitation from mossy fibers to flask-shaped neurons!

The remaining neurons of the granular layer inhibit Purkinje cells!

Afferent cerebellar fibers:

1. Mossy fibers - carry impulses from the bridge and medulla oblongata. Synapses are formed with the dendrites of the granuk cells of the granular layer, and the axons of these cells rise into the molecular layer and transmit impulses to the dendrites of the Purkinje cells directly or through the cells of the molecular layer.

2. Climbing fibers - carry impulses from the spinal cord and from the vestibular apparatus. The climbing fibers do not switch on the cerebellar insertion cells, but pass through the granular and ganglionic layers into the molecular layer and form synapses with dendrites of pear-shaped Purkinje cells there.

Cerebral cortex

The cerebral cortex is represented by a layer of gray matter located on the surface and with a thickness of 3-5 mm. White matter is located under gray!

NERVOUS SYSTEM

Assoc.prof. Kharchenko S.V.
Department of Histology and Embryology
|Medical Academy. S.I. Georgievsky

NERVOUS SYSTEM CONSISTS OF TWO DEPARTMENTS:

- CENTRAL NERVOUS SYSTEM (brain and spinal cord)

- PERIPHERAL NERVOUS SYSTEM (ganglia, peripheral nerves)

 

The brain and spinal cord are composed of gray and white matter.

The main difference between them: gray matter is formed by bodies of neurons, nerve fibers and glia, and white - only by nerve fibers and glia!

The spinal cord (SM) consists of 2 symmetrical halves, separated in front by a deep fissure, and behind by a commissure.

On the cross section, gray and white matter is clearly visible. The gray matter in the section has the shape of a butterfly or the letter "H" and has horns - posterior, lateral and anterior horns.

The abundance of neurocytes determines the gray color of the gray matter. According to morphology, neurocytes of spinal cord are multipolar. The neurocytes in the gray matter are surrounded by nerve fibers tangled up like felt. Axons in nerve fibers are weakly myelinated, and dendrites are not myelinated at all. Similar in size, fine structure and function neurocytes are arranged in groups and form nuclei.

Among the neurocytes of spinal cord the following types are distinguished:

1. Radicular neurocytes - are located in the nuclei of the anterior horns, are motor in function; axons of radicular neurocytes in the structure of the anterior roots leave the SM, conduct motor impulses to the skeletal muscle.

2. Internal cells — the processes of these cells do not leave the gray matter; they terminate within a given segment or an adjacent segment, that is, by function

3. Cells of bundles- the processes of these cells form nerve bundles of white matter and are sent to neighboring segments or overlying sections of the NS, ie by function are also associative.

 

The posterior horns of spinal cord are shorter, narrower and contain the following types of neurocytes:

a) bundle neurocytes - are diffusely located, receive sensitive impulses from the neurocytes of the spinal ganglia and pass along the ascending paths of white matter to the overlying sections of the NS (in the cerebellum, in the cerebral cortex);

b) internal neurocytes - transmit sensitive impulses from the spinal ganglia to the motor neurocytes of the anterior horns and to neighboring segments.

There are 4 structures in the posterior horns of Spinal cord:

1. Spongy substance - consists of small bundle neurocytes and gliocytes.

2. Substancia Gelatinousa - contains a large number of gliocytes, almost no neurocytes.

3. Nucleus proper - consists of bundle neurocytes that transmit impulses to the cerebellum and optic tubercle.

4. Clark's nucleus (Thoracicus nucleus) - consists of bundle neurocytes, the axons of which as part of the lateral cords are sent to the cerebellum.

In the lateral horns (intermediate zone) there are 2 medial intermediate nuclei and a lateral nucleus. Axons of bundle associative neurocytes of the medial intermediate nuclei transmit impulses to the cerebellum. The lateral nucleus of the lateral horns in the thoracic and lumbar spine is the central nucleus of the sympathetic part of the autonomic NS. The axons of the neurocytes of these nuclei go as part of the anterior roots of the spinal cord as preganglionic fibers and end on the neurocytes of the sympathetic trunk (prevertebral and paravertebral sympathetic ganglia). The lateral nucleus in the sacral section of the spinal cord is the central nucleus of the parasympathetic division of the autonomic NS.

Anterior horns contain a large number of motor neurons (motor neurons), forming 2 groups of nuclei:

1. The medial group of nuclei innervates the muscles of the body.

2. The lateral group of nuclei is well expressed in the cervical and lumbar thickening - innervates the muscles of the limbs.

Axons of motor neurons exit the spinal cord in the structure of the anterior roots, reach the skeletal muscles, end on each muscle fiber with a motor plaque.

The white matter of spinal cord consists of longitudinally oriented mainly myelin nerve fibers that form the posterior (ascending), anterior (descending) and lateral (and ascending and descending) cords, as well as glial elements.

The cerebellum is the central organ of balance and coordination of movements.

There are gray and white matter of the cerebellum.

The gray matter is located on the surface of the organ and is represented by the cerebellar cortex and the cerebellar nuclei, which are located in the white matter.

There are 3 layers in the cerebellar cortex:

1. External, molecular, layer - consists of basket -like and star -shaped neurocytes, which are associative in function.

The dendrites of these neurons remain within their layer! And axons go down into the ganglion layer and here they fit in the bodies of Purkinje cells, braid them and form baskets of nerve fibers!

Neurons of this layer inhibit Purkinje cells!

2. The middle, ganglionic layer - consists of 1 row of Purkinje flask-shaped cells (just take off the cerebellum's function of coordinating movement and balance)! These are rather large cells - body diameter up to 60 microns. Dendrites rise into the molecular layer and branch out strongly, are located in the 1st plane, and the axons go into the white matter and form the efferent (outgoing) pathways of the cerebellum and, after switching in the nuclei of the cerebellum, send impulses through the rubrospinal pathway to the spinal cord motor neurons.

3. The inner, granular layer - consists of granuk cells, large stellate neurocytes, spindle-shaped horizontal neurocytes (all cells are associative in function).

Granuk cells are small neurons! Their dendrites branch out in the form of a paw of a bird (there are 3-4 of them in quantity) and form synapses with mossy fibers - these structures are called glomeruli of the cerebellum!

The axons of these cells rise into the molecular layer and there branches T-shaped and runs parallel to the surface of the gray matter! In this case, the axon forms a synapse with the dendrite of the Purkinje cell, thus transmitting excitation from mossy fibers to flask-shaped neurons!

The remaining neurons of the granular layer inhibit Purkinje cells!

Afferent cerebellar fibers:

1. Mossy fibers - carry impulses from the bridge and medulla oblongata. Synapses are formed with the dendrites of the granuk cells of the granular layer, and the axons of these cells rise into the molecular layer and transmit impulses to the dendrites of the Purkinje cells directly or through the cells of the molecular layer.

2. Climbing fibers - carry impulses from the spinal cord and from the vestibular apparatus. The climbing fibers do not switch on the cerebellar insertion cells, but pass through the granular and ganglionic layers into the molecular layer and form synapses with dendrites of pear-shaped Purkinje cells there.

Cerebral cortex

The cerebral cortex is represented by a layer of gray matter located on the surface and with a thickness of 3-5 mm. White matter is located under gray!

In the cortex, there are up to 15 and more billion neurocytes, some authors allow up to 50 billion.