Projection tracts of the posterior cords of the spinal cord. Anterior funiculi of the spinal cord

The spinal cord (medulla spinalis) is located in the spinal canal. At the level of the 1st cervical vertebra and occipital bone, the spinal cord passes into the medulla oblongata, and extends downwards to the level of the 1st–2nd lumbar vertebrae, where it thins out and turns into a thin filament terminale. The length of the spinal cord is 40–45 cm, thickness 1 cm. The spinal cord has cervical and lumbosacral thickenings, where the nerve cells that provide innervation to the upper and lower extremities are localized.

The spinal cord consists of 31–32 segments. A segment is a section of the spinal cord that contains one pair of spinal roots (anterior and posterior).

The anterior root of the spinal cord contains motor fibers, the posterior root contains sensory fibers. Connecting in the area of the intervertebral node, they form a mixed spinal nerve.

The spinal cord is divided into five parts:

Cervical (8 segments);

Thoracic (12 segments);

Lumbar (5 segments);

Sacral (5 segments);

Coccygeal (1–2 rudimentary segments).

The spinal cord is slightly shorter than the spinal canal. In this regard, in the upper parts of the spinal cord, its roots run horizontally. Then, starting from the thoracic region, they descend somewhat downwards before emerging from the corresponding intervertebral foramina. In the lower sections, the roots go straight down, forming the so-called ponytail.

On the surface of the spinal cord, the anterior median fissure, posterior median sulcus, and symmetrically located anterior and posterior lateral sulci are visible. Between the anterior median fissure and the anterior lateral groove is the anterior cord (funiculus anterior), between the anterior and posterior lateral grooves - the lateral cord (funiculus lateralis), between the posterior lateral groove and the posterior median sulcus - the posterior cord (funiculus posterior), which is in the cervical part The spinal cord is divided by a shallow intermediate groove into a thin fasciculus gracilis. adjacent to the posterior median sulcus, and located outward from it, a wedge-shaped bundle (fasciculus cuneatus). The funiculi contain pathways.

The anterior roots emerge from the anterior lateral sulcus, and the dorsal roots enter the spinal cord in the region of the posterior lateral sulcus.

In a cross-section of the spinal cord, the gray matter located in the central parts of the spinal cord and the white matter lying on its periphery are clearly distinguished. Gray matter in a cross section resembles the shape of a butterfly with open wings or the letter “H”. In the gray matter of the spinal cord, more massive ones are distinguished. wide and short anterior horns and thinner, elongated posterior horns. In the thoracic regions, a lateral horn is detected, which is also less pronounced in the lumbar and cervical regions of the spinal cord. The right and left halves of the spinal cord are symmetrical and connected by commissures of gray and white matter. Anterior to the central canal is the anterior gray commissure (comissura grisea anterior), followed by the anterior white commissure (comissura alba anterior); posterior to the central canal, the posterior gray commissure and the posterior white commissure are located successively.

Large motor nerve cells are localized in the anterior horns of the spinal cord, the axons of which go to the anterior roots and innervate the striated muscles of the neck, trunk and limbs. The motor cells of the anterior horns are the final authority in the implementation of any motor act, and also have trophic effects on the striated muscles.

Primary sensory cells are located in the spinal (intervertebral) nodes. Such a nerve cell has one process, which, moving away from it, is divided into two branches. One of them goes to the periphery, where it receives irritation from the skin, muscles, tendons or internal organs. and along another branch these impulses are transmitted to the spinal cord. Depending on the type of irritation and, therefore, the pathway along which it is transmitted, the fibers entering the spinal cord through the dorsal root may end on the cells of the dorsal or lateral horns or directly pass into the white matter of the spinal cord. Thus, the cells of the anterior horns carry out motor functions, the cells of the posterior horns carry out the sensitivity function, and the spinal vegetative centers are localized in the lateral horns.

The white matter of the spinal cord consists of fibers of the pathways that interconnect both the different levels of the spinal cord with each other, and all overlying parts of the central nervous system with the spinal cord.

The anterior cords of the spinal cord contain mainly pathways involved in motor functions:

1) anterior corticospinal (pyramidal) tract (uncrossed) coming mainly from the motor area of the cerebral cortex and ending on the cells of the anterior horns;

2) vestibulospinal tract, coming from the lateral vestibular nucleus of the same side and ending on the cells of the anterior horns;

3) tegmental-spinal tract, starting in the upper colliculi of the quadrigeminal tract of the opposite side and ending on the cells of the anterior horns;

4) the anterior reticular-spinal tract, coming from the cells of the reticular formation of the brain stem of the same side and ending on the cells of the anterior horn.

In addition, near the gray matter there are fibers that connect different segments of the spinal cord with each other.

The lateral cords of the spinal cord contain both motor and sensory PATHWAYS. Motor pathways include:

Lateral corticospinal (pyramidal) tract (crossed) coming mainly from the motor area of the cerebral cortex and ending on the cells of the anterior horns of the opposite side;

The spinal tract, coming from the red nucleus and ending on the cells of the anterior horns of the opposite side;

Reticular-spinal cord tracts, coming predominantly from the giant cell nucleus of the reticular formation of the opposite side and ending on the cells of the anterior horns;

The olivospinal tract connects the inferior olive to the motor neuron of the anterior horn.

The afferent, ascending conductors include the following paths of the lateral cord:

1) posterior (dorsal uncrossed) spinocerebellar tract, coming from the cells of the dorsal horn and ending in the cortex of the superior cerebellar vermis;

2) anterior (crossed) spinocerebellar tract, coming from the cells of the dorsal horns and ending in the cerebellar vermis;

3) the lateral spinothalamic tract, coming from the cells of the dorsal horns and ending in the thalamus.

In addition, the dorsal tegmental tract, spinal reticular tract, spino-olive tract and some other conduction systems pass through the lateral cord.

The afferent thin and cuneate fasciculi are located in the posterior cords of the spinal cord. The fibers included in them begin in the intervertebral nodes and end, respectively, in the nuclei of the thin and wedge-shaped fasciculi, located in the lower part of the medulla oblongata.

Thus, part of the reflex arcs is closed in the spinal cord and the excitation coming through the fibers of the dorsal roots is subjected to a certain analysis and then transmitted to the cells of the anterior horn; the spinal cord transmits impulses to all overlying parts of the central nervous system up to the cerebral cortex.

The reflex can be carried out in the presence of three successive links: 1) the afferent part, which includes receptors and pathways that transmit excitation to the nerve centers; 2) the central part of the reflex arc, where the analysis and synthesis of incoming stimuli occurs and a response to them is developed; 3) the effector part of the reflex arc, where the response is carried out through skeletal muscles, smooth muscles and glands. The spinal cord is thus one of the first stages at which the analysis and synthesis of stimuli both from internal organs and from receptors of the skin and muscles are carried out.

The spinal cord carries out trophic influences, i.e. damage to the nerve cells of the anterior horns leads to disruption of not only movements, but also the trophism of the corresponding muscles, which leads to their degeneration.

One of the important functions of the spinal cord is the regulation of the activity of the pelvic organs. Damage to the spinal centers of these organs or the corresponding roots and nerves leads to persistent disturbances in urination and defecation.

Funiculi medullae spinalis. Three columns of white matter, separated by anterior and posterior horns of gray matter, as well as corresponding radicular filaments.
Anterior funiculus, funiculus anterior. It lies between the anterior median fissure on one side and the anterior horn and its radicular filaments on the other. Rice. A.
Lateral funiculus, funiculus lateralis. Located outside the gray matter between the anterior and posterior roots. Rice. A.
Posterior funiculus, funiculus posterior. Located between the posterior horn and its radicular filaments on one side, and the posterior median septum on the other. Rice. A.
Segments of the spinal cord, segmenta medullae spinalis. Areas of the brain whose radicular filaments form one pair of spinal nerves passing through the corresponding intervertebral foramina. On an isolated spinal cord there are no boundaries between segments.
Cervical segments - cervical part, segmenta cervicalia l - 57 - pars cervicalis. The radicular filaments of segments 1-7 emerge from the spinal canal above the corresponding vertebra number, and the radicular filaments of the eighth segment go below the body of C 7. The cervical part of the spinal cord extends from the atlas to the middle of C 7. Fig. IN.
Thoracic segments = thoracic part, segmenta thoracica = pars thoracica. Located from the middle of C 7 to the middle of T 11. Fig. IN.
Lumbar segments - lumbar part, segmenta lumbalia - pars lumbalis. Projected from the middle of T 11 to the upper edge of the body L 1. Fig. IN.
Sacral segments - sacral part, segmenta sacralia - pars sacralia They lie behind the body L 1. Fig. IN.
Coccygeal segments - coccygeal part, segmenta coccygea - pars coccygea. Three small segments of the spinal cord. Rice. IN.
Sections of the spinal cord, sectiones medullae spinalis. Serve to describe the internal structure of the spinal cord.
Central canal, canalis centralis. Obliterated remnant of the neural tube cavity. Located inside the central intermediate substance. Rice. A, G.
Gray matter, substantia grisea. It is located medially from the white matter and consists of multipolar ganglion cells that form symmetrical solid columns connected to each other along the spinal cord. In cross sections, they correspond to the horns of gray matter, the shape and size of which vary in different parts of the spinal cord. Rice. A.
White matter, substantia alba. Formed by myelinated nerve fibers, which are grouped into pathways and are part of three cords. Rice. A.
Central gelatinous substance, substantia gelatinosa centralis. A narrow zone around the central canal, which consists of processes of ependymal cells.
Gray pillars, columnae griseae. The spinal cord consists of three columns of gray matter. Rice. B.
Anterior column, columna anterior. Consists mainly of motor neurons. Rice. B.
Anterior horn, cornu anterius. Corresponds to the front pillar. Rice. G.
Anterolateral nucleus, nucleus anterolateralis. Located in the anterolateral section of the anterior horn of the fourth - eighth cervical (C4 - 8) and second lumbar - first sacral (L2 - S1) segments of the spinal cord. The neurons of this nucleus innervate the muscles of the limbs. Rice. G.
Anteromedial nucleus, nucleus anteromedialis. Located in the anteromedial part of the anterior horn along the entire length of the spinal cord. Rice. G.
Posterolateral nucleus, nucleus posterolateralis. Located behind the anterolateral nucleus in the fifth cervical - first thoracic (C5 - T1) and second lumbar - second sacral (L2 - S2) segments of the spinal cord. Its neurons innervate the muscles of the limbs. Rice. G.
Posterolateral nucleus, nucleus retroposterolateralis. It lies behind the posterolateral nucleus in the eighth cervical - first thoracic (C8 - T1) and first - third sacral (S1 - 3) segments of the spinal cord. Rice. G.
Posteromedial nucleus, nucleus posteromedialis. It is located next to the white commissure along the first thoracic - third lumbar (T1 - L3) segments of the spinal cord. The neurons of this nucleus probably innervate the muscles of the trunk. Rice. G.
Central nucleus, nucleus centralis. A small group of neurons without clear boundaries in some cervical and lumbar segments. Rice. G.
The nucleus of the accessory nerve, nucleus nervi accessorii (nuc. accessorius). Located in the upper six cervical segments (C1 - b) near the anterolateral nucleus. The processes of the neurons of the nucleus form the spinal part of the accessory nerve. Rice. G.
Nucleus of the phrenic nerve, nucleus nervi phrenici (nuc. phrenicus). Lies in the middle of the anterior horn along the fourth - seventh cervical segments (C4 - 7). Rice. G.

3. Spinal cord pathways

In the intermediate zone there is a central intermediate (gray) substance, the cell processes of which participate in the formation of the spinocerebellar tract. At the level of the cervical segments of the spinal cord, between the anterior and posterior horns, and at the level of the upper thoracic segments, between the lateral and posterior horns, a reticular formation is located in the white matter adjacent to the gray matter. The reticular formation here looks like thin bars of gray matter intersecting in different directions and consists of nerve cells with a large number of processes.

The gray matter of the spinal cord with the posterior and anterior roots of the spinal nerves and its own bundles of white matter bordering the gray matter forms its own, or segmental, apparatus of the spinal cord. The main purpose of the segmental apparatus, as the phylogenetically oldest part of the spinal cord, is to carry out innate reactions (reflexes) in response to stimulation (internal or external). I. P. Pavlov defined this type of activity of the segmental apparatus of the spinal cord with the term “unconditioned reflexes.”

White matter is located outside the gray matter. The grooves of the spinal cord divide the white matter into three cords symmetrically located on the right and left. The anterior funiculus is located between the anterior median fissure and the anterior lateral sulcus. In the white matter posterior to the anterior median fissure, the anterior white commissure is distinguished, which connects the anterior cords of the right and left sides. The posterior funiculus is located between the posterior median and posterior lateral sulci. The lateral funiculus is the area of white matter between the anterior and posterior lateral sulci.

The white matter of the spinal cord is represented by processes of nerve cells. The totality of these processes in the cords of the spinal cord constitute three systems of bundles (tracts, or pathways) of the spinal cord:

1) short bundles of associative fibers connecting segments of the spinal cord located at different levels;

2) ascending (afferent, sensory) bundles heading to the centers of the cerebrum and cerebellum;

3) descending (efferent, motor) bundles going from the brain to the cells of the anterior horns of the spinal cord.

The last two systems of bundles form a new (in contrast to the phylogenetically older segmental apparatus) suprasegmental conduction apparatus of bilateral connections of the spinal cord and brain. In the white matter of the anterior cords there are predominantly descending pathways, in the lateral cords there are both ascending and descending pathways, and in the posterior cords there are ascending pathways.

The anterior funiculus includes the following pathways:

1. The anterior corticospinal (pyramidal) tract is motor and contains processes of giant pyramidal cells (gigantopyramidal neuron). The bundle of nerve fibers forming this path lies near the anterior median fissure, occupying the anteromedial sections of the anterior cord. The pathway transmits impulses of motor reactions from the cerebral cortex to the anterior horns of the spinal cord.

2. The reticular-spinal cord conducts impulses from the reticular formation of the brain to the motor nuclei of the anterior horn of the spinal cord. It is located in the central part of the anterior funiculus, lateral to the corticospinal tract.

3. The anterior spinothalamic tract is located slightly anterior to the reticular spinal tract. Conducts impulses of tactile sensitivity (touch and pressure).

4. The tegmental spinal tract connects the subcortical centers of vision (superior colliculi of the midbrain roof) and hearing (inferior colliculi) with the motor nuclei of the anterior horns of the spinal cord. It is located medial to the anterior corticospinal (pyramidal) tract. The bundle of these fibers is directly adjacent to the anterior median fissure. The presence of this tract allows for reflex protective movements during visual and auditory stimulation.

5. Between the anterior corticospinal (pyramidal) tract in front and the anterior gray commissure in the back is the posterior longitudinal fasciculus. This bundle extends from the brain stem to the upper segments of the spinal cord. The fibers of this bundle conduct nerve impulses that coordinate, in particular, the work of the muscles of the eyeball and neck muscles.

6. The vestibulospinal tract is located on the border of the anterior cord with the lateral cord. This pathway occupies a place in the superficial layers of the white matter of the anterior funiculus of the spinal cord, immediately adjacent to its anterior lateral sulcus. The fibers of this pathway go from the vestibular nuclei of the VIII pair of cranial nerves, located in the medulla oblongata, to the motor cells of the anterior horns of the spinal cord.

The lateral cord of the spinal cord contains the following pathways:

1. The posterior spinocerebellar tract (Flexig's bundle), conducts impulses of proprioceptive sensitivity, occupies the posterolateral sections of the lateral cord near the posterior lateral sulcus. Medially, the bundle of fibers of this pathway is adjacent to the lateral corticospinal (pyramidal) tract, the red nuclear spinal cord and the lateral spinothalamic tract. Anteriorly, the posterior spinocerebellar tract is in contact with the anterior tract of the same name.

2. The anterior spinocerebellar tract (Gowers' bundle), which also carries proprioceptive impulses to the cerebellum, is located in the anterolateral sections of the lateral funiculus. Anteriorly, it adjoins the anterior lateral groove of the spinal cord and borders the olivospinal tract. Medially, the anterior spinocerebellar tract is adjacent to the lateral spinothalamic and spinocerebellar tracts.

3. The lateral spinothalamic tract is localized in the anterior sections of the lateral cord, between the anterior and posterior spinocerebellar tracts on the lateral side, and the red nucleus-spinal and vestibulospinal tracts on the medial side. Conducts impulses of pain and temperature sensitivity.

The descending fiber systems of the lateral cord include the lateral corticospinal (pyramidal) and extrapyramidal red-nuclear-spinal cord pathways.

4. The lateral corticospinal (pyramidal) tract conducts motor impulses from the cerebral cortex to the anterior horns of the spinal cord. The bundle of fibers of this tract, which are processes of giant pyramidal cells, lies medial to the posterior spinocerebellar tract and occupies a significant part of the area of the lateral cord, especially in the upper segments of the spinal cord. In front of this path is the red nucleus-spinal tract. In the lower segments, it occupies less and less area in sections.

5. The red nucleus spinal tract is located anterior to the lateral corticospinal (pyramidal) tract. Adjacent to it laterally in a narrow area are the posterior spinocerebellar tract (its anterior sections) and the lateral spinothalamic tract. The red nucleus-spinal tract is a conductor of impulses for automatic (subconscious) control of movements and tone of skeletal muscles to the anterior horns of the spinal cord.

In the lateral cords of the spinal cord there are also bundles of nerve fibers that form other pathways (for example, spinal tegmental, olivospinal, etc.).

The posterior cord at the level of the cervical and upper thoracic segments of the spinal cord is divided into two bundles by the posterior intermediate sulcus. The medial one is directly adjacent to the posterior longitudinal groove - this is a thin bundle (Gaull's bundle). Its lateral side is adjacent to the posterior horn on the medial side by a wedge-shaped bundle (Burdach's bundle). The thin bundle consists of longer conductors running from the lower torso and lower extremities of the corresponding side to the medulla oblongata. It includes fibers that form part of the dorsal roots of the 19 lower segments of the spinal cord and occupy its more medial part in the posterior cord. Due to the entry into the 12 upper segments of the spinal cord of fibers belonging to neurons innervating the upper limbs and upper part of the body, a wedge-shaped bundle is formed, occupying a lateral position in the posterior cord of the spinal cord. The thin and wedge-shaped bundles are conductors of proprioceptive sensitivity (articular-muscular sense), which carry information about the position of the body and its parts in space to the cerebral cortex.

Topic 2. Structure of the brain

1. Meninges and cavities of the brain

The brain, encephalon, with its surrounding membranes is located in the cavity of the cerebral part of the skull. In this regard, its convex superolateral surface corresponds in shape to the internal concave surface of the cranial vault. The lower surface - the base of the brain - has a complex topography corresponding to the shape of the cranial fossae of the inner base of the skull.

The brain, like the spinal cord, is surrounded by three meninges. These connective tissue sheets cover the brain, and in the area of the foramen magnum they pass into the membranes of the spinal cord. The outermost of these membranes is the dura mater of the brain. It is followed by the middle one - the arachnoid, and inwardly from it there is the inner soft (choroid) membrane of the brain, adjacent to the surface of the brain.

The dura mater of the brain differs from the other two in its special density, strength, and the presence in its composition of a large number of collagen and elastic fibers. Lining the inside of the cranial cavity, the dura mater of the brain is also the periosteum of the inner surface of the bones of the cerebral part of the skull. The hard shell of the brain is loosely connected to the bones of the vault (roof) of the skull and is easily separated from them.

At the inner base of the skull (in the region of the medulla oblongata), the dura mater of the brain fuses with the edges of the foramen magnum and continues into the dura mater of the spinal cord. The inner surface of the dura mater, facing the brain (towards the arachnoid membrane), is smooth.

The largest process of the dura mater of the brain is the falx cerebri (large falciform process), located in the sagittal plane and penetrating into the longitudinal fissure of the cerebrum between the right and left hemispheres. This is a thin crescent-shaped plate of the hard shell, which in the form of two sheets penetrates the longitudinal fissure of the cerebrum. Without reaching the corpus callosum, this plate separates the right and left hemispheres of the cerebrum from each other.

2. Brain mass

The weight of the adult human brain ranges from 1100 to 2000 g; on average, for men it is 1394 g, for women it is 1245 g. The mass and volume of the brain of an adult over the course of 20 to 60 years remain maximum and constant for each given individual. After 60 years, the mass and volume of the brain decrease slightly.

3. Classification of brain parts

When examining a specimen of the brain, its three largest components are clearly visible: the cerebral hemispheres, the cerebellum and the brain stem.

Hemispheres of the cerebrum. In an adult, this is the most highly developed, largest and functionally most important part of the central nervous system. The sections of the cerebral hemispheres cover all other parts of the brain.

The right and left hemispheres are separated from each other by a deep longitudinal fissure of the cerebrum, which in the depths between the hemispheres reaches the large commissure of the brain, or the corpus callosum. In the posterior sections, the longitudinal fissure connects with the transverse fissure of the cerebrum, which separates the cerebral hemispheres from the cerebellum.

On the superolateral, medial and inferior (basal) surfaces of the cerebral hemispheres there are deep and shallow grooves. Deep grooves divide each of the hemispheres into lobes of the cerebrum. Small grooves are separated from each other by the convolutions of the cerebrum.

The lower surface or base of the brain is formed by the ventral surfaces of the cerebral hemispheres, the cerebellum and the most visible ventral parts of the brain stem.

The brain has five sections, developing from five brain vesicles: 1) the telencephalon; 2) diencephalon; 3) midbrain; 4) hindbrain; 5) the medulla oblongata, which at the level of the foramen magnum passes into the spinal cord.

Rice. 7. Parts of the brain

1 - telencephalon; 2 - diencephalon; 3 - midbrain; 4 - bridge; 5 - cerebellum (hindbrain); 6 - spinal cord.

The extensive medial surface of the cerebral hemispheres hangs over the much smaller cerebellum and brain stem. On this surface, as on other surfaces, there are grooves that separate the convolutions of the cerebrum from each other.

The areas of the frontal, parietal and occipital lobes of each hemisphere are separated from the large commissure of the brain, the corpus callosum, which is clearly visible in the median section, by the groove of the same name. Under the corpus callosum there is a thin white plate - the fornix. All formations listed above belong to the telencephalon.

The structures below, with the exception of the cerebellum, belong to the brainstem. The most anterior parts of the brain stem are formed by the right and left visual thalamus - this is the posterior thalamus. The thalamus is located inferior to the body of the fornix and the corpus callosum and behind the column of the fornix. In a midline section, only the medial surface of the posterior thalamus is visible. The interthalamic fusion stands out on it. The medial surface of each posterior thalamus limits the lateral slit-like vertical cavity of the third ventricle. Between the anterior end of the thalamus and the column of the fornix there is an interventricular foramen, through which the lateral ventricle of the cerebral hemisphere communicates with the cavity of the third ventricle. In the posterior direction from the interventricular foramen, the hypothalamic groove stretches around the thalamus from below. The formations located downward from this groove belong to the hypothalamus. These are the optic chiasm, gray tubercle, infundibulum, pituitary gland and mastoid bodies, which participate in the formation of the floor of the third ventricle.

Above and behind the optic thalamus, under the splenium of the corpus callosum, is the pineal body.

The thalamus (optic thalamus), hypothalamus, third ventricle, pineal body belong to the diencephalon.

Caudal to the thalamus are formations related to the midbrain, mesencephalon. Below the pineal gland is the roof of the midbrain (plate quadrigeminal), consisting of the superior and inferior colliculi. The ventral plate of the midbrain roof is the cerebral peduncle, separated from the plate by the midbrain aqueduct. The midbrain aqueduct connects the cavities of the third and fourth ventricles. Even more posteriorly there are midline sections of the pons and cerebellum, related to the hindbrain and a section of the medulla oblongata. The cavity of these parts of the brain is the IV ventricle. The bottom of the IV ventricle is formed by the dorsal surface of the pons and medulla oblongata, which forms a rhomboid fossa on the whole brain. The thin plate of white matter that stretches from the cerebellum to the roof of the midbrain is called the superior medullary velum.

4. Cranial nerves

At the base of the brain, in the anterior sections formed by the lower surface of the frontal lobes of the cerebral hemispheres, olfactory bulbs can be found. They look like small thickenings located on the sides of the longitudinal fissure of the cerebrum. 15-20 thin olfactory nerves (I pair of cranial nerves) approach the ventral surface of each of the olfactory bulbs from the nasal cavity through holes in the ethmoid plate.

A cord stretches back from the olfactory bulb - the olfactory tract. The posterior sections of the olfactory tract thicken and widen, forming the olfactory triangle. The posterior side of the olfactory triangle turns into a small area with a large number of small holes remaining after removal of the choroid. Medial to the perforated substance, closing the posterior sections of the longitudinal fissure of the cerebrum on the lower surface of the brain, there is a thin, gray, easily torn terminal, or terminal, plate. The optic chiasm is adjacent to this plate at the back. It is formed by fibers that are part of the optic nerves (II pair of cranial nerves), penetrating into the cranial cavity from the eye sockets. Two optic tracts extend from the optic chiasm in the posterolateral direction.

A gray tubercle is adjacent to the posterior surface of the optic chiasm. The lower sections of the gray mound are elongated in the form of a tube tapering downward, which is called a funnel. At the lower end of the funnel there is a rounded formation - the pituitary gland, an endocrine gland.

Adjacent to the gray tubercle at the back are two white spherical elevations - the mastoid bodies. Posterior to the optic tracts, two longitudinal white ridges are visible - the cerebral peduncles, between which there is a depression - the interpeduncular fossa, bounded in front by the mastoid bodies. On the medial surfaces of the cerebral peduncles facing each other, the roots of the right and left oculomotor nerves (III pair of cranial nerves) are visible. The lateral surfaces of the cerebral peduncles bend around the trochlear nerves (IV pair of cranial nerves), the roots of which exit the brain not at its base, like all the other 11 pairs of cranial nerves, but on the dorsal surface, behind the lower colliculi of the roof of the midbrain, on the sides of the frenulum superior medullary velum.

The cerebral peduncles posteriorly emerge from the upper parts of a wide transverse ridge, which is designated as the pons. The lateral sections of the pons continue into the cerebellum, forming the paired middle cerebellar peduncle.

At the border between the pons and the middle cerebellar peduncles on each side you can see the root of the trigeminal nerve (V pair of cranial nerves).

Below the bridge are the anterior sections of the medulla oblongata, which are represented by medially located pyramids, separated from each other by the anterior median fissure. Lateral from the pyramid there is a rounded elevation - an olive. At the border of the pons and the medulla oblongata, on the sides of the anterior median fissure, the roots of the abducens nerve (VI pair of cranial nerves) emerge from the brain. Also lateral, between the middle cerebellar peduncle and the olive, on each side the roots of the facial nerve (VII pair of cranial nerves) and the vestibulocochlear nerve (VIII pair of cranial nerves) are sequentially located. The dorsal olive roots in an inconspicuous groove pass from front to back the roots of the following cranial nerves: glossopharyngeal (IX pair), vagus (X pair), and accessory (XI pair). The roots of the accessory nerve also extend from the spinal cord in its upper part - these are the spinal roots. In the groove separating the pyramid from the olive, there are the roots of the hypoglossal nerve (XII pair of cranial nerves).

Topic 4. External and internal structure of the medulla oblongata and pons

1. Medulla oblongata, its nuclei and pathways

The hindbrain and medulla oblongata were formed as a result of the division of the rhomboid vesicle. The hindbrain, metencephalon, includes the pons, located anteriorly (ventrally), and the cerebellum, which is located behind the pons. The cavity of the hindbrain, and with it the medulla oblongata, is the IV ventricle.

The medulla oblongata, medulla oblongata (myelencephalon), is located between the hindbrain and the spinal cord. The upper border of the medulla oblongata on the ventral surface of the brain runs along the lower edge of the pons; on the dorsal surface it corresponds to the medullary stripes of the fourth ventricle, which divide the bottom of the fourth ventricle into upper and lower parts.

The boundary between the medulla oblongata and the spinal cord corresponds to the level of the foramen magnum or the place where the upper part of the roots of the first pair of spinal nerves exits the brain.

The upper sections of the medulla oblongata are somewhat thicker than the lower ones. In this regard, the medulla oblongata takes the shape of a truncated cone or bulb, for its similarity with which it is also called a bulb - bulbus.

The length of the medulla oblongata of an adult is on average 25 mm.

In the medulla oblongata, there are ventral, dorsal and two lateral surfaces, which are separated by grooves. The sulci of the medulla oblongata are a continuation of the sulci of the spinal cord and have the same names: anterior median fissure, posterior median sulcus, anterolateral sulcus, posterolateral sulcus. On both sides of the anterior median fissure on the ventral surface of the medulla oblongata there are convex, gradually tapering pyramidal ridges, pyramides.

In the lower part of the medulla oblongata, the bundles of fibers that make up the pyramids move to the opposite side and enter the lateral cords of the spinal cord. This fiber transition is called the pyramidal decussation. The decussation also serves as the anatomical boundary between the medulla oblongata and the spinal cord. On the side of each pyramid of the medulla oblongata there is an oval eminence - the olive, oliva, which is separated from the pyramid by the anterolateral groove. In this groove, the roots of the hypoglossal nerve (XII pair) emerge from the medulla oblongata.

On the dorsal surface, on the sides of the posterior median sulcus, thin and wedge-shaped bundles of the posterior cords of the spinal cord, separated from each other by the posterior intermediate sulcus, end with thickenings. The thin bundle lying more medially forms a tubercle of the thin nucleus. The lateral location is the wedge-shaped fasciculus, which forms the tubercle of the wedge-shaped nucleus on the side of the tubercle of the thin fasciculus. Dorsal to the olive, from the posterolateral groove of the medulla oblongata - behind the olive groove, the roots of the glossopharyngeal, vagus and accessory nerves (IX, X and XI pairs) emerge.

The dorsal part of the lateral funiculus widens slightly upward. Here it is joined by fibers extending from the wedge-shaped and tender nuclei. Together they form the inferior cerebellar peduncle. The surface of the medulla oblongata, bounded below and laterally by the inferior cerebellar peduncles, participates in the formation of the rhomboid fossa, which is the bottom of the fourth ventricle.

A transverse section through the medulla oblongata at the level of the olives reveals accumulations of white and gray matter. In the inferolateral sections there are the right and left lower olive nuclei.

They are curved in such a way that their hilum faces medially and upward. Slightly above the lower olivary nuclei there is a reticular formation formed by the interweaving of nerve fibers and the nerve cells lying between them and their clusters in the form of small nuclei. Between the lower olive nuclei there is the so-called interolive layer, represented by internal arcuate fibers - processes of cells lying in the thin and wedge-shaped nuclei. These fibers form the medial lemniscus. The fibers of the medial lemniscus belong to the proprioceptive pathway of the cortical direction and form the decussation of the medial lemniscus in the medulla oblongata. In the superolateral parts of the medulla oblongata, the right and left inferior cerebellar peduncles are visible on the section. The fibers of the anterior spinocerebellar and red nuclear spinal tracts pass somewhat ventrally. In the ventral part of the medulla oblongata, on the sides of the anterior median fissure, there are pyramids. Above the intersection of the medial loops is the posterior longitudinal fasciculus.

The medulla oblongata contains the nuclei of the IX, X, XI and XII pairs of cranial nerves, which take part in the innervation of internal organs and derivatives of the branchial apparatus. The ascending pathways to other parts of the brain also pass here. The ventral sections of the medulla oblongata are represented by descending motor pyramidal fibers. Dorsolaterally, ascending pathways pass through the medulla oblongata, connecting the spinal cord with the cerebral hemispheres, brain stem and cerebellum. In the medulla oblongata, as in some other parts of the brain, there is a reticular formation, as well as such vital centers as the circulatory and respiratory centers.

Figure 8.1. The anterior surfaces of the frontal lobes of the cerebral hemispheres, diencephalon and midbrain, pons and medulla oblongata.

III-XII - corresponding pairs of cranial nerves.

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Educational and methodological complex of the discipline “physiology of higher nervous activity and sensory systems”

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Vorotnikova A.I. EDUCATIONAL-METHODICALCOMPLEXDISCIPLINES"Physiology of higher nervous activities and... Centralnervoussystem- (CNS) - includes the spinal cord and brain. Contrasted nervous peripheral system. Central ...

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EDUCATIONAL-METHODICALCOMPLEXDISCIPLINES « ANATOMY nervously systems central departments). Anatomy outdoor...

Educational and methodological complex of the discipline “anatomy, physiology and pathology of organs”

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From___________200 Head of Department_________________ EDUCATIONAL-METHODICALCOMPLEXDISCIPLINES « ANATOMY, physiology and... diphtheria of the larynx); G) nervously- muscle disorders (... speech systems(peripheral, conductive and central departments). Anatomy outdoor...

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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 site of the anterior roots of the spinal cord) on each side there is an anterior cord. Between the anterolateral and posterolateral grooves (the entrance of the dorsal roots) on the surface of the right and left sides of the spinal cord, the lateral cord is formed. Behind the posterolateral sulcus, on each side of the posterior median sulcus, is the posterior cord 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 spinal cord segment. 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 dorsal root, sensitive, is formed by a set of axons of pseudouninolar neurons, whose bodies form the spinal ganglion, located in the spinal canal outside the central nervous system. Information from internal organs enters the spinal cord through this root. Therefore, this spine “enters.” Along the spinal cord, there are 31 pairs of roots on each side, 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 matter, i.e., the cell 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 contain 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 central nervous system do not have direct contact with receptors or effector organs. They exchange information with the periphery through segmental centers of the spinal cord.

6.2.2. White matter

The white matter of the spinal cord makes up the anterior, lateral and posterior cords and is formed mainly by longitudinally running myelinated nerve fibers that form the 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 - posterior (sensitive) root;
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.

Table 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 spinocerebellar;
4- anterior spinocerebellar;
5-spinothalamatic;
6-short spinal;
7- short spinal anterior;
8-rubrospinal;
9-reticulospinal;
10- tectospinal

These grooves divide each half of the white matter of the spinal cord into three longitudinal cords: anterior - funiculus anterior, lateral - funiculus lateralis And posterior - funiculus posterior. The posterior cord in the cervical and upper thoracic regions is further divided intermediate groove, sulcus intermedius posterior, on two bundles: fasciculus gracilis and fasciculus cuneatu s. Both of these bundles, under the same names, pass at the top to the posterior side of the medulla oblongata.

On both sides, the spinal nerve roots emerge from the spinal cord in two longitudinal rows. Anterior root, radix ventral is s. anterior, exiting through sulcus anterolateralis, consists of neurites of motor (centrifugal, or efferent) neurons, the cell bodies of which lie in the spinal cord, whereas posterior root, radix dorsalis s. posterior included in sulcus posterolateralis, contains processes of sensitive (centripetal, or afferent) neurons, the bodies of which lie in spinal nodes.

At some distance from the spinal cord, the motor root is adjacent to the sensory root and together they form spinal nerve trunk, truncus n. spinalis, which neurologists identify under the name funiculus. When the cord is inflamed (funiculitis), segmental disorders of both the motor and sensory spheres occur; in case of root disease (radiculitis), segmental disorders of one sphere are observed - either sensory or motor, and in case of inflammation of the branches of the nerve (neuritis), the disorders correspond to the zone of distribution of this nerve. The nerve trunk is usually very short, since upon exiting the intervertebral foramen the nerve splits into its main branches.

In the intervertebral foramina near the junction of both roots, the dorsal root has a thickening - spinal ganglion, containing false unipolar nerve cells (afferent neurons) with one process, which is then divided into two branches: one of them, the central one, goes as part of the dorsal root into the spinal cord, the other, peripheral, continues into the spinal nerve. Thus, there are no synapses in the spinal ganglia, since only the cell bodies of afferent neurons lie here. This distinguishes the named nodes from the autonomic nodes of the peripheral nervous system, since in the latter intercalary and efferent neurons come into contact. Spinal nodes sacral roots lie inside the sacral canal, and coccygeal root node- inside the sac of the spinal cord.

Due to the fact that the spinal cord is shorter than the spinal canal, the exit site of the nerve roots does not correspond to the level of the intervertebral foramina. To get to the latter, the roots are directed not only to the sides of the brain, but also downwards, and the more vertically they extend from the spinal cord, the more vertical they are. In the lumbar part of the latter nerve roots descend to the corresponding intervertebral foramina in parallel filum terminate, clothing her and conus medullaris a thick bunch, which is called horse tail, cauda equina.