The structure of the spinal cord. Bundles of associative fibers of the posterior cord of the spinal cord and lateral cord of the spinal cord Basic parameters of white matter

second higher education "psychology" in MBA format

subject: Anatomy and evolution of the human nervous system.
Manual "Anatomy of the central nervous system"

6.2. Internal structure of the spinal cord

6.2.1. Gray matter of the spinal cord
6.2.2. white matter

6.3. Reflex arcs of the spinal cord

6.4. Spinal cord pathways

6.1. General overview of the spinal cord
The spinal cord lies in the spinal canal and is a cord 41 - 45 cm long (in an adult of average height. It begins at the level of the lower edge of the foramen magnum, where the brain is located above. The lower part of the spinal cord narrows in the form of a cone of the spinal cord.

Initially, in the second month of intrauterine life, the spinal cord occupies the entire spinal canal, and then, due to faster growth of the spine, it lags in growth and moves upward. Below the level of the end of the spinal cord is the terminal filum, surrounded by the roots of the spinal nerves and the meninges of the spinal cord (Fig. 6.1).

Rice. 6.1. Location of the spinal cord in the spinal canal of the spine :

The spinal cord has two thickenings: cervical and lumbar. In these thickenings there are clusters of neurons that innervate the limbs, and from these thickenings come the nerves going to the arms and legs. In the lumbar region, the roots run parallel to the filum terminale and form a bundle called the cauda equina.

The anterior median fissure and posterior median groove divide the spinal cord into two symmetrical halves. These halves, in turn, have two weakly defined longitudinal grooves, from which emerge the anterior and posterior roots, which then form the spinal nerves. Due to the presence of grooves, each of the halves of the spinal cord is divided into three cords called cords: anterior, lateral and posterior. Between the anterior median fissure and the anterolateral groove (the exit point of the anterior roots of the spinal cord), on each side is the anterior cord. Between the anterolateral and posterolateral grooves (the entrance of the posterior roots) on the surface of the right and left sides of the spinal cord, a lateral funiculus is formed. Behind the posterolateral sulcus, on the sides of the posterior median sulcus, is the posterior funiculus of the spinal cord (Fig. 6.2).

Rice. 6.2. Cords and roots of the spinal cord:

1 - anterior cords;
2 - lateral cords;
3 - posterior cords;
4 - gray still;
5 - anterior roots;
6 - posterior roots;
7 - spinal nerves;
8 - spinal nodes

The section of the spinal cord corresponding to two pairs of spinal nerve roots (two anterior and two posterior, one on each side) is called a segment of the spinal cord. There are 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal segments (31 segments in total) .

The anterior root is formed by the axons of motor neurons. It carries nerve impulses from the spinal cord to the organs. That's why he "comes out." The posterior, sensory root is formed by a collection of axons of pseudouninolar neurons, whose bodies form a spinal ganglion located in the spinal canal outside the central nervous system C. Information from the internal organs enters the spinal cord through this root. Therefore, this spine “enters.” Throughout the spinal cord on each side there are 31 pairs of roots, forming 31 pairs of spinal nerves.

6.2. Internal structure of the spinal cord

The spinal cord consists of gray and white matter. Gray matter is surrounded on all sides by white, that is, the bodies of neurons are surrounded on all sides by pathways.

6.2.1. Gray matter of the spinal cord

In each half of the spinal cord, the gray matter forms two irregularly shaped vertical cords with anterior and posterior projections - columns, connected by a jumper, in the middle of which there is a central canal running along the spinal cord and containing cerebrospinal fluid. At the top, the canal communicates with the fourth ventricle of the brain.

When sliced horizontally, the gray matter resembles a “butterfly” or the letter “H”. There are also lateral projections of gray matter in the thoracic and upper lumbar regions. The gray matter of the spinal cord is formed by the cell bodies of neurons, partially unmyelinated and thin myelinated fibers, as well as neuroglial cells.

The anterior horns of the gray matter contain the bodies of spinal cord neurons that perform motor functions. These are the so-called root cells, since the axons of these cells make up the bulk of the fibers of the anterior roots of the spinal nerves (Fig. 6.3).

Rice. 6.3. Types of spinal cord cells :

As part of the spinal nerves, they are directed to the muscles and are involved in the formation of posture and movements (both voluntary and involuntary). It should be noted here that it is through voluntary movements that all the richness of human interaction with the outside world is realized, as I. M. Sechenov accurately noted in his work “Reflexes of the Brain.” In his conceptual book, the great Russian physiologist wrote: “Whether a child laughs at the sight of a toy... whether a girl trembles at the first thought of love, whether Newton creates the laws of universal gravitation and writes them on paper - everywhere the final fact is muscle movement.”

Another prominent physiologist of the 19th century, Charles Sherrington, introduced the concept of the spinal “funnel”, implying that many descending influences from all levels of the central nervous system converge on the motor neurons of the spinal cord - from the medulla oblongata to the cerebral cortex. To ensure such interaction of the motor cells of the anterior horns with other parts of the central nervous system, a huge number of synapses are formed on motor neurons - up to 10 thousand on one cell, and they themselves are among the largest human cells.

The dorsal horns contain a large number of interneurons (interneurons), with which most of the axons coming from sensory neurons located in the spinal ganglia as part of the dorsal roots are in contact. Spinal cord interneurons are divided into two groups, which in turn are subdivided into smaller populations: inner cells (neurocytus internus) and tuft cells (neurocytus funicularis).

In turn, the inner cells are divided into association neurons, whose axons terminate at different levels within the gray matter of their half of the spinal cord (which provides communication between different levels on one side of the spinal cord), and commissural neurons, whose axons terminate on the opposite side of the spinal cord. brain (this achieves a functional connection between the two halves of the spinal cord). The processes of both types of neurons of the nerve cells of the dorsal horn communicate with the neurons of the upper and lower adjacent segments of the spinal cord; in addition, they can also contact the motor neurons of their segment.

At the level of the thoracic segments, lateral horns appear in the structure of the gray matter. They are the centers of the autonomic nervous system. In the lateral horns of the thoracic and upper segments of the lumbar spinal cord there are spinal centers of the sympathetic nervous system, which innervate the heart, blood vessels, bronchi, digestive tract, and genitourinary system. Here are neurons whose axons are connected to the peripheral sympathetic ganglia (Fig. 6.4).

Rice. 6.4. Somatic and autonomic reflex arc of the spinal cord:

a — somatic reflex arc; b — vegetative reflex arc;
1 - sensitive neuron;
2 - interneuron;
3 - motor neuron;

6 - rear horns;
7 - front horns;
8 - side horns

The nerve centers of the spinal cord are working centers. Their neurons are directly connected to both receptors and working organs. The suprasegmental centers of the CNS do not have direct contact with receptors or effector organs. They exchange information with the periphery through the segmental centers of the spinal cord.

6.2.2. white matter

The white matter of the spinal cord is the anterior, lateral and posterior funiculi and is formed mainly by longitudinally running myelinated nerve fibers that form pathways. There are three main types of fibers:

1) fibers connecting parts of the spinal cord at different levels;
2) motor (descending) fibers coming from the brain in the spinal cord to the motor neurons lying in the anterior horns of the spinal cord and giving rise to the anterior motor roots;
3) sensitive (ascending) fibers, which are partly a continuation of the fibers of the dorsal roots, partly - processes of cells of the spinal cord and ascend upward to the brain.

6.3. Reflex arcs of the spinal cord

The anatomical formations listed above are the morphological substrate of reflexes, including those closed in the spinal cord. The simplest reflex arc includes sensory and effector (motor) neurons, along which the nerve impulse moves from the receptor to the working organ, called the effector (Fig. 6.5, a).

Rice. 6.5. Reflex arcs of the spinal cord:

a - two-neuron reflex arc;
b - three-neuron reflex arc;
1 - sensitive neuron;
2 - interneuron;
3 - motor neuron;
4 — back (sensitive) spine;
5 - anterior (motor) root;
6 - rear horns;
7 - front horns

An example of a simple reflex is the knee reflex, which occurs in response to a short-term stretch of the quadriceps femoris muscle with a light blow to its tendon below the kneecap. After a short latent (hidden) period, the quadriceps muscle contracts, resulting in the lifting of the freely hanging lower leg.
However, most of the spial reflex arcs have a three-neuron structure (Fig. 6.5, b). The body of the first sensory (pseudo-unipolar) neuron is located in the spinal ganglion. Its long process is associated with a receptor that perceives external or internal stimulation. From the neuron body along a short axon, the nerve impulse is sent through the sensory roots of the spinal nerves to the spinal cord, where it forms synapses with the bodies of interneurons. The axons of interneurons can transmit information to the overlying parts of the central nervous system or to motor neurons of the spinal cord. The axon of a motor neuron as part of the anterior roots leaves the spinal cord as part of the spinal nerves and is directed to the working organ, causing a change in its function.

Each spinal reflex, regardless of the function performed, has its own receptive field and its own localization (location), its own level. In addition to motor reflex arcs, at the level of the thoracic and sacral parts of the spinal cord, autonomic reflex arcs are closed, which control the activity of the internal organs by the nervous system.

6.4. Spinal cord pathways

Distinguish ascending and descending tracts of the spinal cord.
According to the first, information from the receptors and the spinal cord itself enters the overlying parts of the central nervous system (Table 6.1), according to the second, information from the higher centers of the brain is sent to the motor neurons of the spinal cord.

Tab. 6.1. The main ascending tracts of the spinal cord:

The location of the pathways on a section of the spinal cord is shown in Fig. 6.6.

Fig 6.6 Spinal cord pathways:

1-tender(thin);
2-maple;
3-posterior dorsal;
4 - anterior spinal cerebellar;
5-spinothalamatic;
6-short spinal;
7- short-spinal anterior;
8-rubrospinal;
9-reticulospinal;
10-tectospinal

The central nervous system (CNS) in the human body is represented by two brain elements: the head and the spinal cord. In the human skeleton there is a spinal canal where the spinal cord is located. What functions does it perform?

It performs two vital functions:

conductor (paths for transmitting pulse signals);
reflex-segmental.

The conduction function is carried out by transmitting an impulse along the ascending cerebral pathways to the brain and back to the executive organs along the descending cerebral pathways. Long tracts for the transmission of impulse signals allow them to be transmitted from the spinal cord to different functional parts of the brain, and short ones provide communication between adjacent segments of the spinal cord.

The reflex function is reproduced by activating a simple reflex arc (knee reflex, extension and flexion of arms and legs). Complex reflexes are reproduced with the participation of the brain. The spinal cord is also responsible for performing autonomic reflexes that control the functioning of the human internal environment - the digestive, urinary, cardiovascular, and reproductive systems. The diagram below illustrates the functions of the autonomic system in the body. The control of autonomic and motor reflexes is carried out due to proprioceptors in the thickness of the spinal cord. The structure and functions of the spinal cord have a number of features in humans.

Let's look at the structure of the spinal cord to better understand what functions it performs.

Anatomical features

The structure of the human spinal cord is not as simple as it might seem at first. Externally, the spinal cord resembles a cord with a diameter of up to 1 cm, a length of 40-45 cm. It originates from the medulla oblongata of the brain and ends with the cauda equina at the end of the spinal column. The vertebrae protect the spinal cord from damage.

The spinal cord is a cord formed by brain tissue. Throughout its entire length, it has a rounded cross-section; the only exceptions are the thickening zones, where its flattening is observed. The cervical thickening is located from the third vertebra of the neck to the first thoracic. The lumbosacral flattening is localized in the region of the 10-12 thoracic vertebrae.

In front and behind the spinal cord on its surface there are grooves that divide the organ into two halves. The medullary cord has three membranes:

hard - is a white, shiny, dense fibrous tissue rich in elastic fibers;
arachnoid - made of connective tissue covered with endothelium;
choroid - a membrane made of loose connective tissue rich in blood vessels to provide nutrition to the spinal cord.

Between the two lower layers is the cerebrospinal fluid (CSF).

The central sections of the spinal cord are made of gray matter. On a preparation of a section of an organ, this substance resembles a butterfly in outline. This component of the brain consists of nerve cell bodies (intercalary and motor type). This part of the nervous system is divided into functional zones: anterior and posterior horns. The former contain motor-type neurons, the latter have intercalary nerve cells. Along the segment of the spinal cord from the 7th cervical segment to the 2nd lumbar segment there are additional lateral horns. It contains centers responsible for the functioning of the autonomic nervous system (nervous system).

The posterior horns are characterized by the heterogeneity of their structure. These zones of the spinal cord contain special nuclei made of interneurons.

The outer part of the spinal cord is formed by white matter, made of axons of butterfly neurons. The spinal grooves conventionally divide the white matter into 3 pairs of cords, known as: lateral, posterior and anterior. Axons unite into several conducting tracts:

associative fibers (short) - provide connection between different spinal segments;
ascending fibers, or sensory fibers, transmit nerve signals to the head section of the central nervous system;
descending fibers, or motor fibers, transmit impulse signals from the cerebral cortex to the anterior horns that control the executive organs.

The posterior cords contain only ascending conductors, and the remaining two pairs are characterized by the presence of descending and ascending pathways. The number of conducting tracts in the cords varies. The table below shows the location of the conduction tracts in the dorsal part of the central nervous system.

Lateral cord conductors:

spinocerebellar tract (posterior) – transmits proprioceptive impulse signals to the cerebellum;
spino-cerebellar tract (anterior) - responsible for communication with the cerebellar cortex, where it transmits impulse signals;
spinothalamic tract (external lateral) - responsible for transmitting impulse signals to the brain from receptors that respond to pain and temperature changes;
pyramidal tract (outer lateral) – conducts motor impulse signals from the cortex of the large hemispheres to the spinal cord;
red nuclear spinal tract - controls the maintenance of skeletal muscle tone and regulates the performance of subconscious (automatic) motor functions.

Anterior cord of conductors:

pyramidal tract (anterior) – transmits the motor signal from the cortex of the upper parts of the central nervous system to the lower ones;
spinothalamic tract (anterior) – transmits impulse signals from tactile receptors;
vestibulospinal - carries out coordination of conscious movements and balance, and is also characterized by the presence of a connection with the medulla oblongata.

Rear cord of conductors:

thin bundle of Gaulle fibers - responsible for transmitting impulse signals from proprioceptors, interoreceptors and skin receptors of the lower torso and legs to the brain;
wedge-shaped bundle of Burdach fibers - is responsible for transmitting the same receptors to the brain from the arms and upper torso.

The human spinal cord in its structure belongs to segmental organs. How many segments does it have in the human body? In total, the cerebral cord contains 31 segments, respectively, of the spine:

in the cervical - eight segments;
in the chest - twelve;
in the lumbar – five;
in the sacrum - five;
in the coccyx - one.

The segments of the medullary cord have four roots that form the spinal nerves. The dorsal roots are formed from the axons of sensory neurons; they enter the dorsal horns. The posterior roots have sensory ganglia (one on each). Then, at this place, a synapse is formed between the sensory and motor cells of the NS. The axons of the latter form the anterior roots. The above diagram shows the structure of the spinal cord and its roots.

In the center of the spinal cord, a canal is localized along its entire length; it is filled with cerebrospinal fluid. To the head, arms, lungs and heart muscle, conducting fibers stretch from the cervical and upper thoracic segments. Segments of the lumbar and thoracic region of the brain give off nerve endings to the muscles of the trunk and abdominal cavity with its contents. The lower lumbar and sacral segments of a person give nerve fibers to the legs and lower abdominal muscles.

Anterior cords contain the following pathways

1) anterior, motor, corticospinal (pyramidal) pathway. This path contains processes of pyramidal cells of the cortex of the anterior central gyrus, which end on the motor cells of the anterior horn of the opposite side, transmits impulses of motor reactions from the cerebral cortex to the anterior horns of the spinal cord;

2) the anterior spinothalamic tract in the middle part of the anterior cord provides the conduction of impulses of tactile sensitivity (touch and pressure);

3) on the border of the anterior cord with the lateral cord there is the vestibular cord, which originates from the vestibular nuclei of the VIII pair of cranial nerves located in the medulla oblongata and goes to the motor cells of the anterior horns. The presence of the tract allows you to maintain balance and coordinate movements.

The lateral funiculi contain the following pathways:

1) the posterior spinocerebellar tract occupies the posterior lateral sections of the lateral funiculi and is a conductor of reflex proprioceptive impulses directed to the cerebellum;

2) the anterior spinocerebellar tract is located in the anterolateral sections of the lateral funiculi, it follows into the cerebellar cortex;

3) lateral spinothalamic tract - the path for conducting impulses of pain and temperature sensitivity, located in the anterior sections of the lateral cord. Of the descending tracts in the lateral cords there are the lateral corticospinal (pyramidal) tract and the extrapyramidal - red nuclear spinal tract;

4) the lateral corticospinal tract is represented by fibers of the main motor pyramidal tract (the path of impulses that causes conscious movements), which lie medial to the posterior spinal cerebellar tract and occupy a significant part of the lateral cord, especially in the upper segments of the spinal cord;

5) the red nuclear-spinal tract is located ventral to the lateral corticospinal (pyramidal) tract. This pathway is a reflex motor efferent pathway.

Brain

The brain is located in the cranial cavity. The brain has a complex shape that matches the topography of the cranial vault and cranial fossae (Fig. 24, 25, 26). The upper lateral parts of the brain are convex, the base is flattened and has many irregularities. At the base of the brain, 12 pairs of cranial nerves depart from the brain.

The weight of the brain in an adult varies from 1100 to 2000. On average, it is 1394 g for men, 1245 g for women. This difference is due to the lower body weight of women.

The brain consists of five sections: medulla oblongata, hindbrain, midbrain, diencephalon and telencephalon.

During an external examination of the brain, the brain stem (Fig. 27, 28, 29), the cerebellum and the cerebrum are distinguished, consisting of the medulla oblongata, pons and midbrain (see Fig. 24, 26). In humans, the cerebral hemispheres cover the remaining parts of the brain in front, above and on the sides; they are separated from each other by the longitudinal fissure of the cerebrum. In the depths of this gap is the corpus callosum, which connects both hemispheres (see Fig. 25). The corpus callosum, like the medial surfaces of the hemispheres, can be seen only after separating the upper edges of the hemispheres and, accordingly, expanding the longitudinal fissure of the cerebrum. In the normal state, the medial surfaces of the hemispheres are quite close to each other; in the skull they are separated only by the large falx of the dura mater. The occipital lobes of the cerebral hemispheres are separated from the cerebellum by the transverse fissure of the cerebrum.

The surfaces of the cerebral hemispheres are streaked with grooves (see Fig. 24, 25,26). Deep primary grooves divide the hemispheres into lobes (frontal, parietal, temporal, occipital), shallow secondary grooves separate narrower areas - gyri. In addition, there are also tertiary grooves that are inconsistent and very variable in different people, which divide the surface of the convolutions and lobules into smaller areas.

When externally examining the brain from the side (see Fig. 24), the cerebral hemispheres are visible; the cerebellum (dorsally) and the pons (ventrally) are adjacent to them below. Below them is visible the medulla oblongata, which passes down into the spinal cord. If you bend the temporal lobe of the cerebrum down, then in the depths of the lateral (Sylvian) fissure you can see the smallest lobe of the cerebrum - the insula.

On the lower surface of the brain (see Fig. 26) structures belonging to all five of its departments are visible. In the front part there are frontal lobes protruding forward, on the sides there are temporal lobes. In the middle part between the temporal lobes (see Fig. 26) the lower surface of the diencephalon, midbrain and medulla oblongata, which passes into the spinal cord, is visible. On the sides of the pons and medulla oblongata the lower surface of the cerebellar hemispheres is visible.

The following anatomical structures are visible on the lower surface (base) of the brain (see Fig. 26). In the olfactory grooves of the frontal lobes there are olfactory bulbs, which pass posteriorly to the olfactory tracts and olfactory triangles. 15–20 olfactory filaments (olfactory nerves) - the first pair of cranial nerves - approach the olfactory bulbs. Posterior to the olfactory triangles on both sides, the anterior perforated substance is visible, through which blood vessels pass deep into the brain. Between both sections of the perforated substance there is a chiasm of the optic nerves (optic chiasm), which are the second pair of cranial nerves.

Posterior to the optic chiasm is a gray tubercle that passes through the infundibulum connected to the pituitary gland (cerebral appendage). Behind the gray tubercle there are two mastoid bodies. These formations belong to the diencephalon, its ventral section - the hypothalamus. The hypothalamus is followed by the cerebral peduncles (structures of the midbrain), and behind them, in the form of a transverse ridge, is the ventral part of the hindbrain - the pons. Between the cerebral peduncles, an interpeduncular fossa opens, the bottom of which is perforated by vessels penetrating deep into the brain - the posterior perforated substance. The cerebral peduncles lying on the sides of the perforated substance connect the pons with the cerebral hemispheres. On the inner surface of each cerebral peduncle, near the anterior edge of the pons, the oculomotor nerve (III pair) emerges, and on the side of the cerebral peduncle - the trochlear nerve (IV pair of cranial nerves).

The thick middle cerebellar peduncles radiate posteriorly and laterally from the pons. The trigeminal nerve (V pair) emerges from the thickness of the middle cerebellar peduncle.

Posterior to the pons is the medulla oblongata. From the transverse groove separating the medulla oblongata from the pons, the abducens nerve (VI pair) emerges medially, and laterally from it the facial nerve (VII pair) and the vestibular nerve (VIII pair of cranial nerves) emerge. On the sides of the median groove of the medulla oblongata, running longitudinally, longitudinal thickenings are visible - pyramids, and on the side of each of them there are olives. From the groove behind the olive from the medulla oblongata, the cranial nerves emerge successively - the glossopharyngeal (IX pair), vagus * (X pair), accessory (XI pair), and from the groove between the pyramid and the olive - the hypoglossal nerve (XII pair of cranial nerves).

Medulla

The medulla oblongata is a direct continuation of the spinal cord (see Fig. 26, 27, 28, 29). Its lower border is considered to be the place of exit of the roots of the 1st cervical spinal nerve or the decussation of the pyramids, the upper border is the lower (posterior) edge of the bridge. The length of the medulla oblongata is about 25 mm, its shape resembles a truncated cone, with its base facing upward, or an onion**.

The anterior surface of the medulla oblongata (see Fig. 26, 27) is separated by the anterior median fissure, which is a continuation of the anterior median fissure of the spinal cord. On the sides of this gap there are longitudinal ridges - pyramids. The pyramids are formed by bundles of nerve fibers of the pyramidal pathways. Fibers of the pyramidal tracts connect the cerebral cortex with the nuclei of the cranial nerves and the anterior horn of the spinal cord, providing conscious movements. On each side of the pyramid there is an olive, separated from the pyramid by the anterior lateral groove.

The posterior surface of the medulla oblongata (see Fig. 29) is divided by the posterior median sulcus, which is a continuation of the posterior median sulcus of the spinal cord. On the sides of this groove there are continuations of the posterior cords of the spinal cord, which diverge upward and pass into the lower cerebellar peduncles. The medial edges of these legs limit the inferior rhomboid fossa, and the place of their divergence forms the lower corner of the said fossa. Each posterior cord in the lower parts of the medulla oblongata consists of two bundles - wedge-shaped (lateral) and thin (medial), on which tubercles containing nuclei are visible near the lower corner of the rhomboid fossa: wedge-shaped (lateral) and thin (medially). In these nuclei, tactile and proprioceptive impulses are switched from the axons of sensitive pseudounipolar neurons to interneurons. The axons of the intercalary cells subsequently move to the opposite side, forming a lemniscus (Latin “lemniscus” - loop), and are directed to specific nuclei of the thalamus.

The medulla oblongata is made up of white and gray matter.

The white matter is formed by nerve fibers that make up the corresponding pathways. The motor pathways (descending) are located in the anterior parts of the medulla oblongata, the sensory (ascending) pathways lie more dorsally.

The gray matter of the medulla oblongata is represented by the nuclei of the IX, X, XI, XII pairs of cranial nerves, the olivary nuclei, the centers of respiration, blood circulation and the reticular formation.

The reticular formation (Latin “formatio reticularis” - mesh formation) is a collection of cells, cell clusters (nuclei) and nerve fibers that form a network located medially in the brain stem (medulla oblongata, pons and midbrain). There is a reticular formation, although less developed, in the spinal cord. Here it is located in the corner between the posterior and anterior horns (or lateral horns, if they are expressed in this segment).

The bodies of neurons in the reticular formation (RF) are surrounded by a mass of tangled fibers, which represent the beginnings and ends of processes going to or extending from the bodies of neurons. Since they appear as tangled fibers when observed under a light microscope, this part of the gray matter was called neuropil (Latin “pilos” - felt). Axons in the neuropil are weakly myelinated, and dendrites do not have a myelin sheath at all. In general, larger neurons are located medially in the reticular formation, forming long ascending and descending axons. Smaller neurons, which are mainly associative, are located laterally in the RF.

The reticular formation is connected to all sense organs, motor and sensory areas of the cerebral cortex, the thalamus and hypothalamus, and the spinal cord. It regulates the level of excitability and tone of various parts of the nervous system, including the cerebral cortex, and is involved in the regulation of the level of consciousness, emotions, sleep and wakefulness, autonomic functions, and purposeful movements.

Above the medulla oblongata are the structures of the hindbrain - the pons (ventrally) and the cerebellum (dorsally).

Bridge

The pons (Varoliev pons), which is a structure of the hindbrain, has the appearance of a transversely lying thickened ridge (see Fig. 24, 25, 26). From the lateral sides of the cerebellum on the right and left, the middle cerebellar peduncles extend back into the depths of the cerebellum. The posterior surface of the pons, covered by the cerebellum, participates in the formation of the rhomboid fossa. Below the pons is the medulla oblongata, the border between them is the lower edge of the pons. Above the pons is the midbrain; the border between them is considered to be the upper edge of the pons.

The anterior surface of the pons is transversely striated due to the transverse direction of the fibers that go from the medially own nuclei of the pons to the middle cerebellar peduncles and further to the cerebellum. On the anterior surface of the bridge along the midline there is a longitudinal basilar groove in which the artery of the same name lies (see Fig. 26). In the frontal section through the bridge, two of its parts are visible: the anterior (main, basilar) and posterior (tire). The boundary between them is a trapezoidal body formed by transversely running fibers of the conductive path of the auditory analyzer.

In the posterior part of the bridge (tegmentum) there is a reticular formation, the nuclei of the V, VI, VII, VIII pairs of cranial nerves lie, and ascending pathways pass.

The anterior (basilar) part of the bridge consists of nerve fibers that form descending pathways, among which there are cell clusters - nuclei. The pathways of the anterior (basilar) part connect the cerebral cortex with the spinal cord, with the motor nuclei of the cranial nerves and with the cerebellar hemisphere cortex. Between the nerve fibers of the pathways lie the own nuclei of the bridge.

Cerebellum

The cerebellum is a structure of the hindbrain; it is located dorsal to the pons, under the occipital poles of the cerebral hemispheres, with which it is separated by the transverse fissure of the cerebrum (see Fig. 24, 25). The cerebellum has two convex hemispheres and the vermis - an unpaired median part (Fig. 31). The vermis is the most ancient part of the cerebellum; the hemispheres formed much later (in mammals).

The surfaces of the hemispheres and the vermis are separated by transverse parallel grooves (fissures), between which there are narrow and long cerebellar gyri - the leaves of the cerebellum. Due to this, its surface area in an adult is on average 850 cm2. The cerebellum has superior and inferior surfaces. The boundary between these surfaces is a deep horizontal fissure running along the posterior edge of the cerebellum. The horizontal fissure originates in the lateral parts of the cerebellum at the point where the middle peduncles enter it. Groups of leaves separated by deep grooves form the cerebellar lobules. Since the cerebellar grooves are continuous and pass from the vermis to the hemispheres, each lobule of the vermis is connected on the right and left sides with the symmetrical lobules of the cerebellar hemispheres.

In section, the cerebellum consists of gray and white matter (Fig. 32). The gray matter of the cerebellum is represented by the cerebellar cortex and cerebellar nuclei. The cerebellar cortex is located on its surface, its thickness is 1–2.5 mm. The white matter and cerebellar nuclei are located within the cerebellum.

Gray matter. Neurons in the cerebellar cortex are located in three layers: the outer layer is molecular, the middle layer is piriform neurons (ganglionic), and the inner layer is granular. The molecular and granular layers contain mainly small neurons. Large piriform neurons (Purkinje cells), measuring up to 80 µm (average 60 µm), are located in the middle layer in one row. These are efferent neurons of the cerebellar cortex. The dendrites of Purkinje cells are located in the superficial molecular layer, and the axons are directed to the neurons of the cerebellar and thalamic nuclei. The remaining neurons of the cerebellar cortex are intercalary (associative), they transmit impulses to piriform neurons.

In the thickness of the white matter of the cerebellum there are accumulations of gray matter - paired nuclei (see Fig. 32). In each half of the cerebellum, the tent nucleus is located closest to the midline. Lateral to it is the spherical nucleus. More lateral is the corky nucleus. The largest and most lateral nucleus of the cerebellum, the dentate nucleus, is located within the cerebellar hemisphere.

White matter of the cerebellum. Afferent and efferent fibers connecting the cerebellum with other parts of the brain form three pairs of cerebellar peduncles (see Fig. 28). The lower legs connect the cerebellum with the medulla oblongata, the middle ones with the pons, the upper ones with the structures of the midbrain, diencephalon and telencephalon.

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Myelinated nerve fibers are grouped into tracts according to the specific direction - to or from the brain - and the type of impulse they receive or transmit. The ascending tracts transmit nerve impulses about all sensations arising in the body up to the . The descending tracts carry impulses from the brain to the skeletal muscles, causing voluntary and involuntary movements.

Pathways of the posterior funiculus:

1. Thin bun ( fasciculus gracilis) is located medially, it contains fibers coming from the lower half of the body, lower extremities through 19 lower spinal nodes and further to the medulla oblongata.

2. Wedge-shaped bundle ( fasciculus cuneatus) is located laterally, in it fibers pass from the upper part of the body through the upper 12 spinal ganglia to the medulla oblongata. Both bundles conduct conscious tactile, proprioceptive sensitivity and a sense of stereognosis.

3. Back own beam ( fasciculus proprius posterior).

Pathways of the lateral funiculus:

4. Side own beam ( fasciculus proprius lateralis).

5. Anterior spinocerebellar tract ( tr. spinocerebellaris anterior).

6. Posterior spinocerebellar tract ( tr. spinocerebellaris posterior).

Both conduct unconscious proprioceptive sensation.

7. Dorsal opercular tract ( tr. spinotectalis).

8. Lateral spinothalamic tract ( tr. spinothalamicus lateralis) - conducts conscious temperature and pain sensitivity.

9. Lateral corticospinal tract ( tr. corticospinalis lateralis) - conscious motor, pyramidal pathway.

10. Red nuclear spinal tract ( tr. rubrospinalis).

11. Olive-spinal fibers ( fibrae olivospinales).

12. Thalamospinal ( tr. thalamospinalis).

Pathways 10 - 12 are unconscious, motor, extrapyramidal.

Pathways of the anterior funiculus:

14. Front own bundle ( fasciculus proprius anterior).

15. Anterior corticospinal tract ( tr. corticospinalis anterior) - conscious, motor pyramidal pathway.

16. Roof-spinal tract ( tr. tectospinalis).

17. Reticulospinal fibers ( fibrae reticulospinalis).

18. vestibulospinal tract ( tr. vestibulospinalis).

Pathways 16 - 18 are unconscious, motor, extrapyramidal.

19. Anterior spinothalamic tract ( tr. spinothalamicus anterior) - conducts conscious tactile sensitivity.

20. Medial longitudinal fasciculus ( fasciculus longitudinalis medialis) is present only in the cervical segments.

Segmental apparatus of the spinal cord- this is a set of nerve structures that ensure the execution of innate reflexes, it includes: dorsal root fibers, intrinsic bundles, nuclei of the anterior horns, scattered cells, cells of the gelatinous substance, spongy and terminal zones.

The conduction apparatus of the spinal cord provides two-way communication between the spinal cord and the integration centers of the brain (cerebellar cortex, cerebral cortex, superior colliculus). This apparatus is represented by sensory and motor pathways.

The integration (suprasegmental) apparatus of the spinal cord includes the ascending and descending tracts, as well as the nuclei: proper, thoracic and medial intermediate.

I. Dorsal (posterior) cords. These are ascending (afferent) pathways formed by collaterals of the axons of sensory neurons of the spinal ganglia. There are two bundles:

· Thin (gentle) bundle (Gaul's bundle). It starts from the lower segments of the spinal cord, is located more medially. Carries information from the receptors of the musculoskeletal system and tactile receptors of the skin of the lower extremities and lower half of the body.

· Wedge-shaped bundle (Bundach's bundle). Appears at the level of 11-12 thoracic segments. Located more laterally. Carries information from the same receptors in the upper half of the body and upper limbs.

II. Lateral (lateral cords). There are ascending and descending paths:

· Ascending pathways (afferent, sensory):

Ø Spinocerebellar tract(Gowers Path) (these are axons of interneurons of the dorsal horns). They transmit signals from the receptors of the musculoskeletal system and tactile receptors of the skin to the cerebellum.

Ø Spinothalamic tract. Axons of interneurons of the dorsal horns transmit signals from pain receptors, thermoreceptors, skin, as well as from all receptors of internal organs (transmit to the thalamus and further to the cerebral cortex (our sensations))

· Descending (efferent) pathways (motor tracts):

Ø Rubrospinal tract- axons of neurons of the red nucleus (Nucleus ruber) of the midbrain, which are directed to the interneurons of the intermediate zone. Features: about neither control the flexor muscles.

Ø Corticospinal (pyramidal) tract. There is a motor zone in the cortex (in the frontal lobe). These are the axons of pyramidal neurons of the motor (motor) zone of the cerebral cortex, which pass through the entire brain stem to interneurons in the intermediate zone of the spinal cord. In humans, 8% of the fibers of this tract terminate directly on the motor neurons of the anterior horns. Path function: voluntary regulation of subtle and precise movements, mainly of the limbs.

III. Ventral (anterior) funiculi. There are ascending and descending tracts.

· Descending tracts:

Ø Vestibulospinal tract. These are axons of neurons of the vestibular nuclei of the brain stem, which end on neurons of the anterior horns. Functions: k control limb extension.

Ø Reticulospinal tract. These are the axons of the neurons of the reticular nuclei of the trunk, which end on the interneurons of the intermediate zone. Functions: control the movement of the torso and ensure the initiation of locomotion (rhythmic movements, for example, running).

The general principle of the brain:

Reflex arc. The activity of the nervous system is carried out according to the reflex principle. Reflex is the body’s response to a stimulus, carried out with the participation and control of the nervous system. RD – This is a chain of neurons along which signals pass during the implementation of a reflex. Protozoa RD consists of two neurons, between which the synapse is called a two-neuron RD or monosynaptic RD. Such RD not much in the body.

There are always 5 functional links in the reflex arc:

1. Receptor- a specialized cell that perceives a stimulus and transforms it into a nervous process.