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

The spinal cord (medulla spinalis) is located in the spinal canal. At the level of the I cervical vertebra and the occipital bone, the spinal cord passes into the oblong, and downwards stretches to the level of the I-II lumbar vertebra, where it becomes thinner and turns into a thin terminal thread. The spinal cord is 40–45 cm long and 1 cm thick. The spinal cord has cervical and lumbosacral thickenings, where nerve cells are located that provide innervation to the upper and lower extremities.

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 region 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 somewhat 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 downward before exiting the corresponding intervertebral foramina. In the lower sections, the roots go straight down, forming the so-called ponytail.

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

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

On a transverse section in the spinal cord, gray matter is clearly distinguished, located in the central parts of the spinal cord, and white matter, lying on its periphery. The gray matter in the transverse section resembles a butterfly with open wings or the letter "H" in shape. In the gray matter of the spinal cord, more massive ones are isolated. wide and short anterior horns and thinner, elongated posterior horns. In the thoracic regions, a lateral horn is revealed, 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 spikes of gray and white matter. Anterior to the central canal is the anterior gray commissure (comissura grisea anterior), then the anterior white commissure (comissura alba anterior); posterior to the central canal are the posterior gray commissure and the posterior white commissure in succession.

In the anterior horns of the spinal cord, large motor nerve cells are localized, 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 on the other 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 posterior root may terminate on the cells of the posterior or lateral horns, or pass directly into the white matter of the spinal cord. Thus, the cells of the anterior horns perform motor functions, the cells of the posterior horns perform the function of sensitivity, and the spinal vegetative centers are localized in the lateral horns.

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

In the anterior cords of the spinal cord, there are mainly pathways involved in the implementation of motor functions:

1) anterior cortical-spinal (pyramidal) path (non-crossed) going mainly from the motor area of the cerebral cortex and ending on the cells of the anterior horns;

2) pre-door-spinal (vestibulospinal) path, coming from the lateral vestibular nucleus of the same side and ending on the cells of the anterior horns;

3) the occlusal-spinal tract, starting in the upper colliculus of the quadrigemina 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.

Both motor and sensory pathways are located in the lateral cords of the spinal cord. Movement paths include:

Lateral cortical-spinal (pyramidal) path (crossed) going 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 tracts, coming mainly from the giant cell nucleus of the reticular formation of the opposite side and ending on the cells of the anterior horns;

Olivospinal tract, connecting the lower olives with the motor neuron of the anterior horn.

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

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

2) anterior (crossed) dorsal-cerebellar path, coming from the cells of the posterior horns and ending in the cerebellar vermis;

3) the lateral dorsal-thalamic pathway, coming from the cells of the posterior horns and ending in the thalamus.

In addition, in the lateral funiculus, the dorsal-cover way, dorsal-reticular way, spinal-olive way and some other conductor systems pass.

In the posterior funiculi of the spinal cord are afferent thin and wedge-shaped bundles. The fibers included in them begin in the intervertebral nodes and end, respectively, in the nuclei of the thin and wedge-shaped bundles 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 posterior 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 consecutive 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 take place and a response to them is developed; 3) the effector part of the reflex arc, where the response occurs through the skeletal muscles, smooth muscles and glands. The spinal cord, therefore, is one of the first stages at which the analysis and synthesis of stimuli are carried out both from the internal organs and from the receptors of the skin and muscles.

The spinal cord carries out trophic influences, i.e. damage to the nerve cells of the anterior horns leads to a violation 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. The defeat of the spinal centers of these organs or the corresponding roots and nerves leads to persistent disorders of urination and defecation.

Cords of the spinal cord, funiculi medullae spinalis. Three columns of white matter, separated by anterior and posterior horns of gray matter, as well as the corresponding radicular filaments.
Anterior cord, funiculus anterior. It lies between the anterior median fissure on one side, the anterior horn and its radicular filaments on the other. Rice. A.
Lateral cord, funiculus lateralis. It is located outside the gray matter between the anterior and posterior roots. Rice. A.
Posterior cord, funiculus posterior. It is located between the posterior horn and its radicular threads on the one hand, the posterior median septum on the other. Rice. A.
Segments of the spinal cord, segmenta medullae spinalis. Areas of the brain, the radicular threads of which form one pair of spinal nerves passing through the corresponding intervertebral foramens. There are no boundaries between segments on an isolated spinal cord.
Neck segments - cervical part, segmenta cervicalia l - 57 - pars cervicalis. The radicular filaments of segments 1-7 emerge from the spinal canal above the vertebra corresponding to them by number, and the radicular filaments of the eighth segment go below the body C7. The cervical part of the spinal cord extends from the atlas to the middle of C7. IN.
Thoracic segments = thoracic part, segmenta thoracica = pars thoracica. They are located along the length from the middle of C 7 to the middle of T 11. Fig. IN.
Lumbar segments - lumbar part, segmenta lumbalia - pars lumbalis. They are 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 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. They are used to describe the internal structure of the spinal cord.
Central canal, canalis centralis. Obliterated remnant of the neural tube cavity. Located within the central intermediate. Rice. Ah, G.
Gray matter, substantia grisea. It is located medially from the white matter and consists of multipolar ganglion cells that form symmetrical solid columns interconnected throughout the spinal cord. On transverse 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. It is formed by myelinated nerve fibers, which are grouped into pathways and are part of the three cords. Rice. A.
Central gelatinous substance, substantia gelatinosa centralis. A narrow area around the central canal, which consists of processes of ependymal cells.
Gray pillars, columnae griseae. There are three columns of gray matter in the spinal cord. Rice. B.
Front 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. It is located in the anterolateral part 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.
Anterior medial nucleus, nucleus anteromedialis. It is located in the anteromedial section of the anterior horn throughout the spinal cord. Rice. G.
The posterolateral nucleus, nucleus posterolateralis. It is 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.
The 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.
Posterior medial 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. Small in size, without clear boundaries, a group of neurons in some cervical and lumbar segments. Rice. G.
Accessory nerve core, 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.
The 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. Pathways of the spinal cord

In the intermediate zone is located the central intermediate (gray) substance, the processes of the cells of which are involved in the formation of the spinal cerebellar 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 in the white matter adjacent to the gray, there is a reticular formation. The reticular formation here looks like thin crossbars 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 white matter bundles 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 the implementation of innate reactions (reflexes) in response to stimulation (internal or external). IP Pavlov defined this type of activity of the segmental apparatus of the spinal cord with the term "unconditioned reflexes".

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

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 consists of 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 bundle systems form a new (in contrast to the phylogenetically older segmental apparatus) suprasegmental conductor apparatus of bilateral connections between the spinal cord and the brain. In the white matter of the anterior cords there are predominantly descending pathways, in the lateral cords - both ascending and descending pathways, in the posterior cords there are ascending pathways.

The anterior cord includes the following pathways:

1. Anterior cortical-spinal (pyramidal) path - motor, contains processes of giant pyramidal cells (giant pyramidal neuron). The bundle of nerve fibers that form this path lies near the anterior median fissure, occupying the anteromedial sections of the anterior funiculus. The conducting path transmits impulses of motor reactions from the cerebral cortex to the anterior horns of the spinal cord.

2. The reticular-spinal path 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 cord, lateral to the corticospinal tract.

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

4. The operculo-spinal tract connects the subcortical centers of vision (upper mounds of the roof of the midbrain) and hearing (lower mounds) with the motor nuclei of the anterior horns of the spinal cord. It is located medial to the anterior corticospinal (pyramidal) tract. A bundle of these fibers is directly adjacent to the anterior median fissure. The presence of this tract makes it possible to carry out reflex protective movements during visual and auditory stimuli.

5. Between the anterior cortical-spinal (pyramidal) path in front and the anterior gray commissure behind, there is a posterior longitudinal bundle. This bundle extends from the brainstem 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 vestibulo-spinal tract is located on the border of the anterior funiculus with the lateral one. This path occupies a place in the superficial layers of the white matter of the anterior funiculus of the spinal cord, directly near its anterior lateral groove. The fibers of this path 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 funiculus of the spinal cord contains the following pathways:

1. The posterior dorsal cerebellar pathway (Flexig's bundle), conducts impulses of proprioceptive sensitivity, occupies the posterolateral parts of the lateral funiculus near the posterior lateral sulcus. Medially, the bundle of fibers of this conducting tract is adjacent to the lateral cortical-spinal (pyramidal) tract, the red-nuclear-spinal and lateral spinal-thalamic tracts. Ahead, the posterior dorsal cerebellar path is in contact with the anterior path of the same name.

2. The anterior dorsal cerebellar pathway (Govers bundle), which also carries proprioceptive impulses to the cerebellum, is located in the anterolateral sections of the lateral funiculus. Ahead, it adjoins the anterior lateral groove of the spinal cord, borders on the olivospinal tract. Medially, the anterior spinal cerebellar tract is adjacent to the lateral spinal thalamic and spinal tegmental tracts.

3. The lateral spinal-thalamic tract is localized in the anterior sections of the lateral funiculus, between the anterior and posterior spinal cerebellar tracts on the lateral side, the red nuclear-spinal and vestibulo-spinal tracts on the medial side. Conducts impulses of pain and temperature sensitivity.

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

4. The lateral cortical-spinal (pyramidal) path conducts motor impulses from the cerebral cortex to the anterior horns of the spinal cord. A bundle of fibers of this pathway, which are processes of giant pyramidal cells, lies medial to the posterior spinal cerebellar tract and occupies a significant part of the area of the lateral funiculus, especially in the upper segments of the spinal cord. Ahead of this path is the red nuclear-spinal pathway. In the lower segments, it occupies a smaller and smaller area on sections.

5. The red nuclear-spinal tract is located anterior to the lateral cortical-spinal (pyramidal) tract. Laterally, in a narrow area, the posterior spinal-cerebellar path (its anterior sections) and the lateral spinal-thalamic path are adjacent to it. The red nuclear-spinal tract is a conductor of impulses for automatic (subconscious) control of movements and skeletal muscle tone to the anterior horns of the spinal cord.

In the lateral funiculi of the spinal cord, there are also bundles of nerve fibers that form other pathways (for example, dorsal-opercular, olivo-spinal, 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 groove. The medial is directly adjacent to the posterior longitudinal groove - this is a thin bundle (Gaulle's bundle). Its lateral adjoins from the medial side to the posterior horn a wedge-shaped bundle (Burdakh's bundle). The thin bundle consists of longer conductors running from the lower parts of the trunk and lower extremities of the corresponding side to the medulla oblongata. It includes fibers that are part of the posterior 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 the fibers belonging to the neurons innervating the upper limbs and the upper body, a wedge-shaped bundle is formed, which occupies a lateral position in the posterior funiculus of the spinal cord. Thin and wedge-shaped bundles are conductors of proprioceptive sensitivity (articular-muscular feeling), which carry information about the position of the body and its parts in space to the cerebral cortex.

Topic 2. The structure of the brain

1. Shells and cavities of the brain

The brain, encephalon, with the membranes surrounding it, is located in the cavity of the cerebral part of the skull. In this regard, its convex upper-lateral surface corresponds in shape to the inner concave surface of the cranial vault. The lower surface - the base of the brain - has a complex relief 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 region 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 - arachnoid, and medially from it is the inner soft (vascular) membrane of the brain, adjacent to the surface of the brain.

The hard shell of the brain shell differs from the other two in its special density, strength, the presence in its composition of a large number of collagen and elastic fibers. Lined from 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 with the bones of the vault (roof) of the skull and is easily separated from them.

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

The largest process of the dura mater of the brain is located in the sagittal plane and penetrating into the longitudinal fissure of the cerebrum between the right and left hemispheres of the crescent cerebrum (large falciform process). This is a thin sickle-shaped plate of the hard shell, which in the form of two sheets penetrates into the longitudinal fissure of the cerebrum. Before reaching the corpus callosum, this plate separates the right and left hemispheres of the brain from each other.

2. Mass of the brain

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

3. Classification of brain regions

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

Hemispheres of the brain. In an adult, it is the most highly developed, largest and functionally most important part of the central nervous system. The parts 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 large brain, which in depth between the hemispheres reaches a large commissure of the brain, or 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 upper-lateral, medial and lower (basal) surfaces of the cerebral hemispheres there are deep and shallow grooves. Deep furrows divide each of the hemispheres into lobes of the large brain. Small furrows are separated from each other by the convolutions of the large brain.

The lower surface or base of the brain is formed by the ventral surfaces of the cerebral hemispheres, the cerebellum, and the ventral sections of the brain stem that are most accessible here for viewing.

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

Rice. 7. Departments 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 large brain 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 on the median section, by the sulcus of the same name. Under the corpus callosum is a thin white plate - the vault. All the formations listed above belong to the final brain, telencephalon.

The structures below, with the exception of the cerebellum, belong to the brainstem. The most anterior sections of the brain stem are formed by the right and left visual tubercles - this is the posterior thalamus. The thalamus is located inferior to the body of the fornix and corpus callosum and behind the column of the fornix. On the median section, only the medial surface of the posterior thalamus is visible. It stands out interthalamic fusion. 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 is the 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 opening, the hypothalamic sulcus stretches around the thalamus from below. The formations located downward from this furrow belong to the hypothalamus. These are the optic chiasm, gray tubercle, funnel, pituitary gland and mastoid bodies involved in the formation of the bottom of the third ventricle.

Above and behind the visual tubercle, under the roller of the corpus callosum, is the pineal body.

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

Caudal to the thalamus are formations related to the midbrain, mesencephalon. Below the pineal body is the roof of the midbrain (lamina quadrigemina), consisting of the upper and lower hillocks. The ventral plate of the roof of the midbrain is the stalk of the brain, separated from the plate by the aqueduct of the midbrain. The aqueduct of the midbrain connects the cavities of the III and IV ventricles. Even more posteriorly are the median sections of the bridge and the cerebellum, related to the hindbrain and the 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 the medulla oblongata, which forms a diamond-shaped fossa on the whole brain. The thin plate of white matter that extends from the cerebellum to the roof of the midbrain is called the superior medullary velum.

4. Cranial nerves

On the basis 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 large brain. To the ventral surface of each of the olfactory bulbs from the nasal cavity through the holes in the plate of the ethmoid bone, 15-20 thin olfactory nerves (I pair of cranial nerves) approach.

A cord stretches back from the olfactory bulb - the olfactory tract. The posterior sections of the olfactory tract thicken and expand, forming an olfactory triangle. The back side of the olfactory triangle passes 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 final, or terminal, plate. Behind this plate is the optic chiasm. It is formed by fibers that follow in the composition of the optic nerves (II pair of cranial nerves), penetrating into the cranial cavity from the orbits. Two optic tracts depart 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 tubercle are elongated in the form of a tube tapering downwards, which is called a funnel. At the lower end of the funnel is a rounded formation - the pituitary gland, the endocrine gland.

Two white spherical elevations, the mastoid bodies, adjoin the gray tubercle behind. Behind the visual tracts, two longitudinal white rollers are visible - the legs of the brain, between which there is a recess - the interpeduncular fossa, bounded in front by the mastoid bodies. On the medial, facing each other surfaces of the legs of the brain, the roots of the right and left oculomotor nerves (III pair of cranial nerves) are visible. The lateral surfaces of the legs of the brain go around the trochlear nerves (IV pair of cranial nerves), the roots of which exit the brain not on the basis of it, like in all the other 11 pairs of cranial nerves, but on the dorsal surface, behind the lower mounds of the roof of the midbrain, on the sides of the frenulum superior medullary velum.

The legs of the brain emerge from the upper sections of the wide transverse ridge, which is referred to as the bridge. The lateral sections of the bridge continue into the cerebellum, forming a paired middle cerebellar peduncle.

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

Below the bridge are the anterior sections of the medulla oblongata, which are medially located pyramids, separated from each other by the anterior median fissure. Lateral from the pyramid is a rounded elevation - olive. At the border of the bridge and the medulla oblongata, on the sides of the anterior median fissure, the roots of the abducens nerve (the VI pair of cranial nerves) emerge from the brain. Still 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 successively located. Dorsal olives in an inconspicuous groove pass from front to back roots of the following cranial nerves: glossopharyngeal (IX pair), vagus (X pair), and accessory (XI pair). The roots of the accessory nerve also depart from the spinal cord in its upper part - these are the spinal roots. In the groove separating the pyramid from the olive, there are 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 brain bladder. The hindbrain, metencephalon, includes the pons located in front (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 (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 bridge, on the dorsal surface it corresponds to the cerebral stripes of the IV ventricle, which divide the bottom of the IV 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 thickened compared to the lower ones. In this regard, the medulla oblongata takes the form of a truncated cone or bulb, for the similarity with which it is also called the bulb - bulbus, bulbus.

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

In the medulla oblongata, ventral, dorsal and two lateral surfaces are distinguished, which are separated by furrows. The sulci of the medulla oblongata are a continuation of the sulci of the spinal cord and bear 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 are convex, gradually tapering downward pyramidal rollers, pyramides.

In the lower part of the medulla oblongata, the fiber bundles that make up the pyramids pass to the opposite side and enter the lateral cords of the spinal cord. This transition of fibers is called the decussation of the pyramids. The place of decussation also serves as an anatomical boundary between the medulla oblongata and the spinal cord. On the side of each pyramid of the medulla oblongata is an oval elevation - 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, the thin and wedge-shaped bundles of the posterior cords of the spinal cord end with thickenings, separated from each other by the posterior intermediate sulcus. The thin bundle lying more medially forms a tubercle of the thin nucleus. The lateral is a wedge-shaped bundle, which, on the side of the tubercle of a thin bundle, forms a tubercle of the sphenoid nucleus. Dorsal to the olive from the posterolateral sulcus of the medulla oblongata - behind the olive sulcus, the roots of the glossopharyngeal, vagus and accessory nerves (IX, X and XI pairs) emerge.

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

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

They are curved in such a way that their gates face medially and upwards. Slightly above the lower olive nuclei is the 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 is the so-called interolive layer, represented by internal arcuate fibers, processes of cells lying in thin and wedge-shaped nuclei. These fibers form the medial loop. The fibers of the medial loop belong to the proprioceptive pathway of the cortical direction and form a decussation of the medial loops in the medulla oblongata. In the upper lateral sections of the medulla oblongata, the right and left lower cerebellar peduncles are visible on the cut. Several ventral fibers of the anterior spinal-cerebellar and red nuclear-spinal tracts pass. In the ventral part of the medulla oblongata, on the sides of the anterior median fissure, are the pyramids. Above the intersection of the medial loops is the posterior longitudinal bundle.

In the medulla oblongata lie the nuclei of the IX, X, XI and XII pairs of cranial nerves, which are involved in the innervation of the internal organs and derivatives of the branchial apparatus. There are also ascending pathways to other parts of the brain. The ventral parts 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, the brain stem, and the 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 centers of blood circulation and respiration.

Fig 8.1. Anterior surfaces of the frontal lobes of the cerebral hemispheres, diencephalon, 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. Opposed 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, conductor 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. Pathways of the spinal cord

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 starts 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 the faster growth of the spine, lags behind in growth and moves upward. Below the level of the end of the spinal cord is the terminal thread, surrounded by the roots of the spinal nerves and the membranes 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 are clusters of neurons that innervate the limbs, and from these thickenings nerves go to the arms and legs. In the lumbar region, the roots run parallel to the terminal thread and form a bundle called the cauda equina.

The anterior median fissure and the posterior median groove divide the spinal cord into two symmetrical halves. These halves, in turn, have two slightly pronounced longitudinal grooves, from which the anterior and posterior roots emerge, which then form the spinal nerves. Due to the presence of furrows, each of the halves of the spinal cord is divided into three strands, 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 - rear funiculus;
4 - gray stillness;
5 - front roots;
6 - back 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 (motor) neurons. Through it, nerve impulses are sent from the spinal cord to the organs. That's why he "gets 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 "includes". 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 is made up 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 of the halves of the spinal cord, the gray matter forms two irregularly shaped vertical strands with anterior and posterior protrusions - pillars connected by a bridge, in the middle of which there is a central canal that runs along the spinal cord and contains cerebrospinal fluid. At the top, the canal communicates with the fourth ventricle of the brain.

When cut 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 bodies of neurons, partially unmyelinated and thin myelinated fibers, as well as neuroglial cells.

In the anterior horns of the gray matter are the bodies of spinal cord neurons that perform a motor function. These are the so-called radicular 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 cells in the spinal cord :

As part of the spinal nerves, they are sent to the muscles and participate 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 carried out, 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 down on paper—everywhere the ultimate fact is muscle movement.”

Another prominent physiologist of the 19th century, C. Sherrington, introduced the concept of a spinal "funnel", implying that many descending influences converge on the motor neurons of the spinal cord from all levels of the central nervous system - 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 per cell, and they themselves are among the largest human cells.

The posterior 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 posterior roots contact. Interneurons of the spinal cord are divided into two groups, which, in turn, are divided into smaller populations - these are internal cells (neurocytus internus) and beam cells (neurocytus funicularis).

In turn, the internal cells are divided into associative 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 in the nerve cells of the posterior horn communicate with the neurons of the superior and underlying 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 that innervate the heart, blood vessels, bronchi, digestive tract, and genitourinary system. Here are the 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 - autonomic reflex arc;
1 - sensitive neuron;
2 - intercalary neuron;
3 - motor neuron;

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

The nerve centers of the spinal cord are working centers. Their neurons are directly connected with 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 to the spinal cord to motor neurons lying in the anterior horns of the spinal cord and giving rise to the anterior motor roots;
3) sensory (ascending) fibers, which are partly a continuation of the fibers of the posterior roots, partly processes of spinal cord cells 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 that close 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 - intercalary neuron;
3 - motor neuron;
4 — back (sensitive) spine;
5 - anterior (motor) root;
6 - rear horns;
7 - front horns

An example of the simplest reflex is the knee reflex, which occurs in response to a short-term stretching of the quadriceps femoris muscle with a light blow to its tendon below the patella. After a short latent (hidden) period, the quadriceps contraction occurs, as a result of which the freely hanging lower leg rises.
However, most of the spial reflex arcs have a three-neuron structure (Fig. 6.5, b). The body of the first sensitive (pseudo-unipolar) neuron is located in the spinal ganglion. Its long process is associated with a receptor that perceives external or internal irritation. From the body of the neuron along a short axon, the nerve impulse through the sensory roots of the spinal nerves is sent to the spinal cord, where it forms synapses with the bodies of intercalary neurons. The axons of the intercalary neurons can transmit information to the overlying parts of the CNS or to the motor neurons of the spinal cord. The axon of the motor neuron as part of the anterior roots leaves the spinal cord as part of the spinal nerves and goes 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, vegetative reflex arcs are closed, which control the nervous system over the activity of internal organs.

6.4. Pathways of the spinal cord

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 sections 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. Main ascending tracts of the spinal cord:

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

Fig 6.6 Conducting pathways of the spinal cord:

1-gentle (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

These grooves divide each half of the white matter of the spinal cord into three longitudinal cords: anterior - funiculus anterior, lateral - funiculus lateralis And rear - funiculus posterior. The posterior cord in the cervical and upper thoracic regions is further divided intermediate groove, sulcus intermedius posterior, on two beams: 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 roots of the spinal nerves emerge from the spinal cord in two longitudinal rows. Anterior root, radix ventral is s. anterior, coming out through sulcus anterolateralis, consists of neurites of motor (centrifugal, or efferent) neurons, the cell bodies of which lie in the spinal cord, while 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 neuropathologists distinguish under the name cord, funiculus. With inflammation of the cord (funiculitis), segmental disorders occur simultaneously in the motor and sensory spheres; with root disease (sciatica), segmental disorders of one sphere are observed - either sensitive or motor, and with inflammation of the nerve branches (neuritis), the disorders correspond to the distribution zone of this nerve. The trunk of the nerve is usually very short, because after exiting the intervertebral foramen, the nerve splits into its main branches.

In the intervertebral foramina near the junction of both roots, the posterior root has a thickening - spinal ganglion, ganglion spinale, containing false unipolar nerve cells (afferent neurons) with one process, which then divides into two branches: one of them, the central one, goes as part of the posterior root to the spinal cord, the other, peripheral, continues into the spinal nerve. Thus, there are no synapses in the spinal nodes, since only the cell bodies of afferent neurons lie here. In this way, these nodes differ 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 knot- inside the sac of the dura mater of the spinal cord.

Due to the fact that the spinal cord is shorter than the spinal canal, the exit point of the nerve roots does not correspond to the level of the intervertebral foramina. To get into the latter, the roots are directed not only to the sides of the brain, but also down, and the more sheer, the lower they depart from the spinal cord. In the lumbar region of the last nerve roots descend to the corresponding intervertebral foramina in parallel filum terminate wrapping it up and conus medullaris dense bundle, which is called ponytail, cauda equina.