Spinal cord. The spinal cord (medulla spinalis) is located in the spinal canal
Separated by the anterior median fissure and contain descending conductors from the anterior central gyrus, stem and subcortical formations to the anterior horns of the spinal cord.
* spinothalamic pathway
(conducts pain, temperature and partially tactile sensitivity)
* medial loop
(common path of all types of sensitivity. They end in the thalamus)
* bulbothalamic pathway
(conductor of articular-muscular, tatkil, vibrational sensitivity, feeling of pressure, weight. Proprioreceptors are located in muscles, joints, ligaments, etc.)
* a loop trigeminal nerve
(joins the inner loop, approaching it from the other side)
* lateral loop
(auditory pathway brain stem. Ends in the internal geniculate body and the posterior tubercle of the quadrigemina)
* spino-cerebellar pathways
(carry proprioceptive information to the cerebellum. The Gowers bundle begins at the periphery in the proprioceptors)
* posterior spin-cerebellar pathway
(flexic sheaf) has the same origin
№30 Physiology of the spinal cord. Bell–Magendie law
The spinal cord has two functions: reflex and conduction. As a reflex center, the spinal cord is able to carry out complex motor and autonomic reflexes. Afferent - sensitive - ways it is connected with receptors, and efferent - with skeletal muscles and all internal organs. The spinal cord connects the periphery with the brain through long ascending and descending pathways. Afferent impulses along the pathways of the spinal cord are carried to the brain, carrying information about changes in the external and internal environment of the body. Downward pathways impulses from the brain are transmitted to the effector neurons of the spinal cord and cause or regulate their activity.
reflex function. The nerve centers of the spinal cord are segmental or working centers. Their neurons are directly connected with receptors and working organs. In addition to the spinal cord, such centers are found in the medulla oblongata and midbrain. The suprasegmental centers have no direct connection with the periphery. They govern it through segmental centers. The motor neurons of the spinal cord innervate all the muscles of the trunk, limbs, neck, as well as the respiratory muscles - the diaphragm and intercostal muscles. Beyond the motor centers skeletal muscles, in the spinal cord there are a number of sympathetic and parasympathetic autonomic centers. In the lateral horns of the thoracic and upper segments lumbar The spinal cord contains the spinal centers of the sympathetic nervous system that innervate the heart, blood vessels, sweat glands, digestive tract, skeletal muscles, i.e. all organs and tissues of the body. It is here that neurons lie that are directly connected with the peripheral sympathetic ganglia. In the upper thoracic segment, there is a sympathetic center for pupil dilation, in the five upper thoracic segments - sympathetic cardiac centers. In the sacral spinal cord, there are parasympathetic centers innervating the pelvic organs (reflex centers for urination, defecation, erection, ejaculation). The spinal cord has a segmental structure. A segment is a segment that gives rise to two pairs of roots. If the back roots of a frog are cut on one side and the front roots on the other, then the paws on the side where the back roots are cut lose sensitivity, and on the opposite side, where the front roots are cut, they will be paralyzed. Consequently, the posterior roots of the spinal cord are sensitive, and the anterior roots are motor. Each segment of the spinal cord innervates three transverse segments, or metameres, of the body: its own, one above and one below. Skeletal muscles also receive motor innervation from three adjacent segments of the spinal cord. The most important vital center of the spinal cord is the motor center of the diaphragm, located in the III-IV cervical segments. Damage to it leads to death due to respiratory arrest.
The conduction function of the spinal cord. The spinal cord performs a conductive function due to the ascending and descending pathways passing through the white matter of the spinal cord. These pathways connect individual segments of the spinal cord with each other, as well as with the brain.
Bella - Magendie law in anatomy and physiology, the main regularity in the distribution of motor and sensory fibers in the nerve roots of the spinal cord. B. - M. h. established in 1822 by the French physiologist F. Magendie. It was partly based on the observations of the English anatomist and physiologist C. Bell published in 1811. According to B. - M. z., centrifugal (motor) nerve fibers exit the spinal cord as part of the anterior roots, and centripetal (sensory) fibers enter the spinal cord as part of the posterior roots. Centrifugal nerve fibers also exit through the anterior roots, innervating smooth muscles, vessels and glands.
№ 31 Segmental and intersegmental principle of the spinal cord
The spinal cord is a cylindrical cord, covered with membranes, freely located in the cavity of the spinal canal. At the top, it passes into the medulla oblongata; at the bottom, the spinal cord reaches the region of the 1st or upper edge of the 2nd lumbar vertebra. The diameter of the spinal cord is not the same everywhere, in two places two spindle-shaped thickenings are found: in the cervical region - cervical thickening - intumescentia cervicalis (from the 4th cervical to the 2nd thoracic vertebra); at the very bottom thoracic- lumbar thickening - intumescentia lumbalis - (from the 12th thoracic to the 2nd sacral vertebra). Both thickenings correspond to the areas of closure of reflex arcs from the upper and lower extremities. The formation of these thickenings is closely related to segmental principle structures of the spinal cord. There are a total of 31-32 segments in the spinal cord: 8 cervical (C I - C VIII), 12 thoracic (Th I -Th XII), 5 lumbar (L I -L V), 5 sacral (S I -S V) and 1 - 2 coccygeal (Co I - C II).
The lumbar thickening passes into a short cone-shaped section, into the medullary cone - from which a long thin terminal thread departs.
Segmental and intersegmental principle of the spinal cord: The spinal cord is characterized by a segmental structure, reflecting the segmental structure of the body of vertebrates. Two pairs of ventral and dorsal roots depart from each spinal segment. 1 sensory and 1 motor root innervates its transverse layer of the body i.e. metamer. This is the segmental principle of the spinal cord. The intersegment principle of operation is in the innervation by the sensory and motor roots of its metamere, the 1st overlying and 1st underlying metamere. Knowing the boundaries of body metameres makes it possible to carry out topical diagnostics of diseases of the spinal cord. 3. The conduction organization of the spinal cord The axons of the spinal ganglia and gray matter of the spinal cord go to its white matter, and then to other structures of the central nervous system, thereby creating the so-called conducting pathways, functionally subdivided into proprioceptive, spinocerebral (ascending) and cerebrospinal (descending). Propriospinal pathways connect neurons of one or different segments of the spinal cord. The function of such connections is associative and consists in the coordination of posture, muscle tone, movements of various body metameres.
№33 Physiological characteristic cranio- cerebral nerves
Cranial nerves - 12 pairs of nerves emerging from the medulla at the base of the brain and innervating the structures of the skull, face, neck.
The motor nerves originate in the motor nuclei of the trunk. The predominantly motor nerves include a group of oculomotor nerves: oculomotor (3rd), block (4th), abducens (6th), and also facial (7th), which controls mainly facial muscles, but also contains fibers of taste sensitivity and autonomic fibers that regulate the function of the lacrimal and salivary glands, accessory (11th), innervating the sternocleidomastoid and trapezius muscles, hyoid (12th), innervating the muscles of the tongue.
Sensory neurons are formed from the fibers of those neurons whose bodies lie in the cranial ganglia outside the brain. Sensitive ones include olfactory (1st), visual (2nd), vestibulocochlear, or auditory (8th), which provide, respectively, smell, vision, hearing and vestibular function.
The mixed nerves include the trigeminal (5th), which provides facial sensitivity and control of the masticatory muscles, as well as the glossopharyngeal (9th) and vagus (10th), which provide sensitivity to the posterior parts of the oral cavity, pharynx and larynx, as well as the functioning of the muscles pharynx and larynx. The vagus also provides parasympathetic innervation. internal organs.
The cranial nerves are designated by Roman numerals in the order of their location:
I - olfactory nerve;
II - optic nerve;
III - oculomotor nerve;
IV - trochlear nerve;
V - trigeminal nerve;
VI - abducens nerve;
VII - facial nerve;
VIII - vestibulocochlear nerve;
IX - glossopharyngeal nerve;
X- nervus vagus;
XI - accessory nerve;
XII - hypoglossal nerve
No. 32 Medulla oblongata and pons. Their structure and functional value
Structure and meaning medulla oblongata subject to the general laws of the structure of the nervous system (the entire nervous system consists of gray and white matter). The medulla oblongata is integral part rhomboid brain and is a direct continuation of the spinal cord. The medulla oblongata is divided into several parts by the same furrows as the spinal cord. On the sides of one of them (the anterior median sulcus) are the so-called pyramids of the medulla (it turns out that, as it were, the anterior cords of the spinal cord continue into these pyramids).
In these pyramids, the intersection of nerve fibers occurs. On the back side of the medulla oblongata runs the posterior median sulcus, on the sides of which lie the posterior cords of the medulla oblongata. In these posterior cords of the medulla oblongata are the continuation of the sensitive thin and wedge-shaped bundles. Three pairs of cranial nerves come out of the medulla oblongata - IX, X, XI pairs, which are respectively called - glossopharyngeal nerve, vagus nerve, accessory nerve. Also, the medulla oblongata takes part in the formation of the rhomboid fossa, which is the bottom of the 4th ventricle of the brain. In this 4th ventricle (more precisely, in the rhomboid fossa), the vasomotor and respiratory centers are located, if damaged, death occurs instantly. The internal structure of the medulla oblongata is very complex. It contains several nuclei of gray matter:
1. The core of the olive is an intermediate center of balance.
2. Reticular formation - a network of nerve fibers and their processes, passing throughout the entire brain, carries out the relationship and coordination of all brain structures.
3. nuclei of the cranial nerves described above.
4. Vasomotor and respiratory center
In the white matter of the medulla oblongata are fibers: long and short. Short ones carry out the relationship of various structures of the medulla oblongata itself, and long ones - the connection of the medulla oblongata with other structures of the central nervous system.
Bridge - ventral part of the hindbrain, represents a massive protrusion on the ventral surface of the brainstem (hindbrain).
Ventral the surface of the bridge faces the slope of the skull, dorsal participates in the formation of the rhomboid fossa.
* In the lateral direction, the bridge continues into a massive middle cerebellar peduncle leading to the cerebellum. At the border with the bridge, the trigeminal nerve (V) emerges from the pedicle. On the ventral surface of the bridge there is a shallow groove in which the basilar (main) artery lies. On its dorsal surface, on the border with the medulla oblongata, white cerebral stripes are visible, running transversely.
Inside the bridge there is a powerful bundle of transverse fibers called the trapezoid body, which divides the bridge into ventral and dorsal parts.
In the ventral part of the pons, there are own pontine nuclei, which are connected to the cerebral cortex with the help of cortical-bridge fibers. The axons of the pons' own nuclei, forming pontocerebellar fibers, go through the middle cerebellar peduncles to the cerebellar cortex. Through these connections, the cerebral cortex influences the activity of the cerebellum. Pyramid paths run at the base of the bridge.
The dorsal part of the bridge is located dorsally from the trapezius body, here are the nuclei of the trigeminal (V), abducens (VI), facial (VII) and vestibulocochlear (VIII) cranial nerves. In the central sections of the dorsal part of the bridge, along its entire length, there is a reticular formation. In the lateral sections of the dorsal part, there is a medial loop.
Functions of the pons: conductive and reflex. In this department there are centers that control the activity of facial and chewing and one of the oculomotor muscles. The pons receives nerve impulses from the receptors of the sense organs located on the head: from the tongue (taste sensitivity), inner ear(auditory sensitivity and balance) and skin.
№34 Anatomy and physiology of sensory cranial nerves
The cranial nerves are called peripheral nerves that originate from parts of the brain, and the nuclei of these nerves are laid in the brainstem (midbrain, pons and cerebellum).
Most cranial nerves enter the skull through the hindbrain. The cranial nerves III, IV, and VI control the six external muscles of the eye, which carry out the movements of this organ. Cranial nerves V (trigeminal) receive sensory information and transmit nimble signals to mandible, and VII pairs (facial) carry sensory information from the structures of the hyoid arch. The eighth cranial nerves (auditory) contain sensory fibers that are involved in hearing and maintaining balance. The IXth pair of cranial nerves (glossopharyngeal nerve) nerves the pharyngeal arch, carrying both sensory and agile signals.
Touch:
Olfactory nerve (Olfactory nerves sensitive in function, consists of nerve fibers, which are processes of the olfactory cells of the olfactory organ. These fibers form 15-20 olfactory filaments (nerves) that leave the olfactory organ and enter the cranial cavity through the ethmoid plate of the mesh bone, where they approach the neurons of the olfactory bulb, nerve impulses are transmitted through various formations of the peripheral olfactory brain to its central section.)
Visual (optic nerve sensitive in function, consists of nerve fibers, which are processes of the so-called ganglion cells of the retina of the eyeball. From the orbit through the optic canal, the nerve passes into the cranial cavity, where it immediately forms a partial intersection with the nerve of the opposite side (optic chiasm) and continues into the optic tract. Due to the fact that only the medial half of the nerve passes to the opposite side, the right optic tract contains nerve fibers from the right halves, and the left tract from the left halves of the retina of both eyeballs. The visual tracts approach the subcortical visual centers - the nuclei of the upper hillocks of the roof of the midbrain, the lateral geniculate bodies and the pillows of the thalamus. The nuclei of the superior colliculi are connected to the nuclei of the oculomotor nerve (through them pupillary reflex) and with the nuclei of the anterior horns of the spinal cord (orienting reflexes to sudden light stimuli are carried out). From the nuclei of the lateral geniculate bodies and the pillows of the thalamus, the nerve fibers in the composition of the white matter of the hemispheres follow to the cortex of the occipital lobes (visual sensory cortex).)
Spatial-cochlear(a nerve of special sensitivity, consisting of two roots of different function: the vestibular root, which carries impulses from the static apparatus, represented by the semicircular ducts of the vestibular labyrinth, and the cochlear root, which conducts auditory impulses from the spiral organ of the cochlear labyrinth. VIII pair - the vestibulocochlear nerve - connects the hearing organs , equilibrium and gravity)
№35 Anatomy and physiology of motor cranial nerves
(III, IV, VI, XI and XII pairs) - motor nerves:
oculomotor nerve(according to the motor function, it consists of motor somatic and efferent parasympathetic nerve fibers. These fibers are the axons of the neurons that make up the nuclei of the nerve. There are motor nuclei and an additional parasympathetic nucleus. They are located in the brain stem at the level of the upper mounds of the roof of the midbrain. The nerve exits the cavity of the skull through the superior orbital fissure into the orbit and is divided into two branches: superior and inferior.The motor somatic fibers of these branches innervate the superior, medial, inferior rectus and inferior oblique muscles of the eyeball, as well as the muscle that lifts the upper eyelid (they are all striated) , and the parasympathetic fibers - the muscle that narrows the pupil, and the ciliary muscle (both smooth. Parasympathetic fibers switch on the way to the muscles in the ciliary node, which lies in the posterior part of the orbit.)
Block nerve(according to the motor function, it consists of nerve fibers extending from the nucleus. The nucleus is located in the legs of the brain at the level of the lower mounds of the roof of the midbrain. The nerves exit the cranial cavity through the superior orbital fissure into the orbit and innervates the superior oblique muscle of the eyeball.)
Abducens nerve(by function, the motor consists of nerve fibers extending from the neurons of the nerve nucleus located in the bridge. It exits the skull through the superior orbital fissure into the orbit and innervates the lateral (external) rectus muscle of the eyeball.)
facial nerve(mixed in function, includes motor somatic fibers, secretory parasympathetic fibers and sensory taste fibers. Motor fibers depart from the nucleus of the facial nerve located in the bridge. Secretory parasympathetic and sensory taste fibers are part of the intermediate nerve, which has parasympathetic and sensory nuclei in the bridge and exits the brain near the facial nerve.Both nerves (both facial and intermediate) follow into the internal auditory canal, in which the intermediate nerve enters the facial.After that, the facial nerve penetrates into the canal of the same name, located in the pyramid temporal bone. In the canal, it gives off several branches: a large stony nerve, a drum string, etc. A large stony nerve contains secretory parasympathetic fibers to the lacrimal gland. The drum string passes through the tympanic cavity and, leaving it, joins the lingual nerve from the third branch of the trigeminal nerve; it contains taste fibers for the taste buds of the body and the tip of the tongue, and secretory parasympathetic fibers in the submandibular and sublingual salivary glands.)
accessory nerve(according to the motor function, it consists of nerve fibers extending from the neurons of the motor nuclei. These nuclei are located in the medulla oblongata and in the cervical segment of the spinal cord. The nerve exits the skull through the jugular foramen to the neck and innervates the sternomastoidal and trapezius muscles.)
hypoglossal nerve(The nucleus of the hypoglossal nerve is motor, lies in the middle sections of the posterior part of the medulla oblongata. From the side of the rhomboid fossa, it is projected in the region of the triangle of the hypoglossal nerve. The nucleus of the hypoglossal nerve consists of large multipolar cells and a large number of fibers located between them, by which it is divided into three more or less isolated cell groups innervates the muscles of the tongue: the styloglossus, hyoidoglossus and genioglossus muscles, as well as the transverse and rectus muscles of the tongue.)
№36 Anatomy and physiology of mixed cranial nerves
Trigeminal nerve(It consists of three branches. Of these, the first two are sensitive, the third contains both sensory and motor fibers. On the basis of the brain, it is shown from the thickness of the pons varolii at the point of departure from the last middle cerebellar peduncle in two parts: sensory and motor roots.
Both parts are directed forward and somewhat laterally and penetrate into the gap between the sheets of hard tissue. meninges. Along the sensitive root, between its leaves, a trigeminal cavity is formed, located on the trigeminal impression of the top of the temporal bone pyramid. The cavity contains a relatively large (15 to 18 mm long) trigeminal ganglion, which is concave posteriorly and convex anteriorly. Three main branches of the trigeminal nerve depart from its anterior convex edge: ophthalmic, maxillary and mandibular nerves.
The motor root goes around the trigeminal ganglion from the inside, goes to the foramen ovale, where it enters into the third branch of the trigeminal nerve. V pair - trigeminal nerve - innervates the masticatory muscles)
Glossopharyngeal(The glossopharyngeal nerve appears on the lower surface of the brain 4-6 roots behind the olive, below the vestibulocochlear nerve (VIII pair of cranial nerves). It goes outward and forward and exits the skull through the anterior part of the jugular foramen. In the region of the hole, the nerve thickens somewhat due to the superior ganglion located here). Having exited through the jugular foramen, the glossopharyngeal nerve thickens again due to the lower ganglion), which lies in a stony dimple on the lower surface of the temporal bone pyramid. IX pair - Provides: motor innervation of the stylo-pharyngeal muscle, raising the pharynx; innervation of the parotid gland; providing it secretory function; general sensitivity of the pharynx, tonsils, soft palate, eustachian tube, tympanic cavity taste sensation in the posterior third of the tongue.)
№37 Cerebellum, its structure and functions
Cerebellum lies under the occipital lobes of the cerebral hemispheres, separated from it by a horizontal fissure and located in the posterior cranial fossa.
The nuclei of the cerebellum developed in parallel with its development and are paired accumulations of gray matter, lying deep in the white, closer to the "worm". Distinguish:
* jagged;
* corky;
* spherical,
* the core of the tent.
Anterior to it is the bridge and the medulla oblongata.
Cerebellum consists of two hemispheres, in each of which the upper and lower surfaces are distinguished.
In addition, the cerebellum has middle part - worm separating the hemispheres from each other.
Gray matter the cerebellar cortex, consisting of the bodies of neurons, is divided into lobules by deep furrows. Smaller furrows separate the leaves of the cerebellum from each other.
Cerebellar cortex branches and penetrates into the white matter, which is the body of the cerebellum, formed by the processes of nerve cells.
white matter, branching, penetrates into the gyrus in the form of white plates.
The gray matter contains paired nuclei, lying deep in the cerebellum and forming the core of the tent, related to the vestibular apparatus. Lateral to the tent are the spherical and cork-shaped nuclei, which are responsible for the work of the muscles of the body, then the dentate nucleus, which controls the work of the limbs.
The cerebellum communicates with the periphery through other parts of the brain, with which it is connected by three pairs of legs.
- upper legs connect the cerebellum to the midbrain
- medium- with a bridge
- lower- with the medulla oblongata (spinal-cerebellar bundle of Flexic and bundles of Gaulle and Burdach)
Functions of the cerebellum
The main function of the cerebellum- coordination of movements, however, in addition to this, it performs some autonomic functions, taking part in managing the activity of autonomic organs and partly controlling skeletal muscles.
The cerebellum performs three main functions
1. coordination of movements
2. balance regulation
3. regulation muscle tone
№38 Diencephalon, its structure and functions
The structure of the diencephalon. It consists of two parts - the thalamus and the hypothalamus. The hypothalamus acts as the highest organ vegetative system. Physiologically, it is associated with the pituitary gland, so it is discussed in the endocrine system section.
The structure of man assigned a very important function to the diencephalon. It cannot even be separated and specifically named - the diencephalon is involved in the regulation of almost all processes in the body.
The thalamic brain consists of three parts - the thalamus itself, the epithalamus and the metathalamus.
The thalamus occupies the most significant part of the diencephalon. He is large cluster gray matter in the lateral walls on the sides of the diencephalon. The thalamus can be divided into two parts - the anterior end and the pad. This division is not accidental. The fact is that these two parts are functionally different parts - the small pillow is the visual center, and the front part is the center of the afferent (sensitive) pathways. The thalamus, through the so-called (part of the white matter), is very closely connected with the subcortical system, and, in particular, with the caudate nucleus.
Functions: Collection and evaluation of all incoming inf-and from org-s senses. Isolation and transmission to the cerebral cortex of the most important information. regulation of emotional behavior. The highest subcortical center of the vegetative NS and all vital fun-th org-ma. Ensuring the constancy of the internal environment and exchange processes-owls org-ma. Regulation of motivated behavior and defensive reactions(thirst. Hunger, satiety, fear, rage, not/pleasure) Participation in the change of sleep and wakefulness.
№39 Ascending pathways of the spinal cord, medulla oblongata, pons varolii and cerebral peduncles
The structure of the spinal cord
Spinal cord, medulla spinalis (Greek myelos), lies in spinal canal and in adults it is a long (45 cm in men and 41-42 cm in women), a cylindrical cord somewhat flattened from front to back, which at the top (cranially) directly passes into the medulla oblongata, and at the bottom (caudally) ends with a conical sharpening, conus medullaris, at level II of the lumbar vertebra. Knowing this fact is of practical importance (so as not to damage the spinal cord during a lumbar puncture in order to take cerebrospinal fluid or to spinal anesthesia, it is necessary to insert a syringe needle between the spinous processes of the III and IV lumbar vertebrae).
From the conus medullaris, the so-called terminal thread , filum terminale, representing the atrophied lower part of the spinal cord, which below consists of a continuation of the membranes of the spinal cord and is attached to the II coccygeal vertebra.
The spinal cord along its course has two thickenings corresponding to the roots of the nerves of the upper and lower extremities: the upper one is called cervical enlargement , intumescentia cervicalis, and the lower one - lumbosacral , intumescentia lumbosacralis. Of these thickenings, the lumbosacral is more extensive, but the cervical is more differentiated, which is associated with a more complex innervation of the hand as a labor organ. Formed as a result of thickening of the side walls of the spinal tube and passing along the midline anterior and posterior longitudinal grooves : deep fissura mediana anterior, and superficial, sulcus medianus posterior, the spinal cord is divided into two symmetrical halves - right and left; each of them, in turn, has a slightly pronounced longitudinal groove running along the line of entry of the posterior roots (sulcus posterolateralis) and along the line of exit of the anterior roots (sulcus anterolateralis).
These grooves divide each half of the white matter of the spinal cord into three longitudinal cords: front - funiculus anterior, side - funiculus lateralis and rear - funiculus posterior. The posterior cord in the cervical and upper thoracic regions is also divided by an intermediate groove, sulcus intermedius posterior, into two bundles: fasciculus gracilis and fasciculus cuneatus . 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. front spine , radix ventral is s. anterior, exiting through sulcus anterolateralis, consists of neurites motor (centrifugal, or efferent) neurons, whose cell bodies lie in the spinal cord, while back spine , radix dorsalis s. posterior, included in sulcus posterolateralis, contains processes sensory (centripetal, or afferent) neurons whose bodies lie in the spinal nodes.
At some distance from the spinal cord, the motor root is adjacent to the sensory and together they form the trunk of the spinal nerve, truncus n. spinalis, which neuropathologists distinguish under the name of the funiculus, funiculus. Inflammation of the cord (funiculitis) causes segmental disorders of both 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 is then divided 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. The spinal nodes of the sacral roots lie inside the sacral canal, and the node of the coccygeal root lies 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 part of the last nerve roots descend to the corresponding intervertebral foramens parallel to the filum terminate, enveloping it and the conus medullaris in a thick bundle, which is called ponytail , cauda equina.
SPINAL CORD.
Spinal cord, medulla spipalis(Greek muelos), lies in the spinal canal and in adults it is a long, somewhat flattened front-to-back cylindrical strand from the for.magnum level to L I (in men) and L II (in women).
External building.
In the spinal cord there are:
Cervical thickening, intumescentia cervicalis, - the area of the spinal cord that provides innervation upper limbs, located from C5 to Th1;
The lumbosacral thickening, intumescentia lumbosacralis, is the area of the spinal cord that provides innervation to the lower extremities, located from Th12 to S3;
brain cone , conus medullaris, - lower, narrowed section of the spinal cord;
Terminal thread, filum teminale;
Anterior median fissure, fissura mediana anterior;
Posterior median fissure, sulcus medianus posterior;
The anterior lateral sulcus, sulcus ventrolateralis, is the exit point of the anterior roots of the spinal nerves;
The posterior lateral groove, sulcus dorsolateralis, is the exit point of the posterior roots of the spinal nerves; the posterior root has a thickening - the spinal ganglion, ganglion spinale, containing false unipolar nerve cells.
Throughout the SM, 124 roots depart: 62 posterior and 62 anterior (of which 31 pairs of spinal nerves are formed):
The posterior root of the spinal nerve is a collection of central processes of pseudo-unipolar cells that go from the spinal ganglion to the spinal cord;
The anterior root of the spinal nerve is a collection of axons of the cells of the motor nuclei of the anterior horns of the spinal cord, heading from the exit point of their anterior lateral sulcus of the spinal cord to the entrance to the spinal nerve.
spinal cord segment- SC section corresponding to two pairs of spinal nerve roots located at the same level in the horizontal plane.
In the spinal cord, 31 segments are distinguished, which are topographically divided into 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal.
Ponytail, cauda equina, is a collection of spinal nerve roots extending from ten lower segments and terminal thread (40 roots: 20 front and 20 back).
Internal structure of the spinal cord.
1. Gray matter, substantia grisea , on the transverse section, the CM is located inside and has the shape of a butterfly; it is represented mainly by the bodies of nerve cells. More than 90% of the gray matter are scattered cells, cellulae dissiminatae. In the middle of it there is a narrow central canal, canalis centralis, of the spinal cord, which runs the entire length of the latter and contains cerebrospinal fluid. The central canal is a remnant of the cavity of the primary neural tube. Therefore, at the top it communicates with the IV ventricle of the brain, and in the region of the conus medullaris it ends with an expansion - the terminal ventricle ventriculus terminalis.
In the gray matter, SM is isolated:
1) anterior horn, cornu anterius , which contains its own nuclei, nuclei proprii cornu anterius;
2) rear horn, cornu osterius , which has
Proprietary nucleus of the posterior horn, nucleus proprius cornu posterioris;
Thoracic nucleus, nucleus thoracicus; in the thoracic segments, it is called the Clarke nucleus, in the cervical segments, the Stilling nucleus;
Gelatinous substance, substantia gelatinosa, located in the region of the apex of the posterior horn;
The spongy zone, zona spongiosa, is located dorsal to the gelatinous substance;
The border zone, zona terminalis, is the outermost layer back horns.
3) lateral horn, cornu laterale , located in segments C8 - L3; it contains the lateral intermediate nucleus, nucleus intermediolateralis;
4) intermediate substance, substantia intermedia , - the central part of the gray matter; it contains:
Medial intermediate nucleus, nucleus intermediomedialis;
The sacral parasympathetic nuclei, nuclei parasympathici sacrales, are located in the sacral segments (S2 - S4) between the anterior and posterior horns;
Spinal nucleus of the accessory nerve, nucieus spinalis n.accessorii, (in segments C1 - C6);
The nucleus of the spinal tract of the trigeminal nerve, nucieus spinalis n.trigemini, (at the base of the posterior horn of segments C1 - C4).
2. White matter, substantia alba.
White matter consists mainly of processes (myelin fibers) of nerve cells that form:
1) anterior cord, funiculus anterior, limited fissura mediana anterior and s.dorsolateralis;
2) the lateral cord, funiculus lateralis, is limited to s.ventrolateralis and s.dorsolateralis;
3) the posterior cord, funiculus posterior, is limited to s.medianus posterior and s.dorsolateralis.
Each cord consists of bundles of nerve fibers (axons), which are combined according to the commonality of their origin and functional purpose into the nerve tracts.
COMPOSITION OF THE CORDS OF THE SPINAL CORD.
Posterior cords contain afferent (ascending, sensitive) pathways:
1) thin bundle, fasciculus gracilis (Gaul's bundle); a thin bundle is formed by the axons of the spinal ganglion of its side. It conducts impulses of proprioceptive and tactile sensitivity from the lower extremities and torso (from 19 lower segments).
2) wedge-shaped bundle , fasciculus cuneatus (Burdach's bundle); conducts impulses of proprioceptive and tactile sensitivity from the upper limbs and upper body (from the 12 upper segments).
3) rear own beam , fasciculus proprius posterior; formed by axons of intercalary neurons of the segmental apparatus.
4) posterior root fibers that form radicular zone , zona radicularis.
Lateral cords contain the following pathways:
A. Ascending.
To the hindbrain:
1) posterior spinal cerebellar path , tractus spinocerebellaris posterior, (Flexig's bundle), is located in the back of the lateral cord along its periphery; formed by the axons of the nucleus thoracicus of its side, conducts impulses of unconscious proprioceptive sensitivity to the cerebellum.
2), anterior spinal cerebellar tract , tractus spinocerebellaris anterior, lies ventral to the previous one; conducts unconscious proprioceptive impulses.
To the midbrain:
3) dorsal tract, tractus spinotestalis, adjacent to the medial side and the anterior part of the tractus spinocerebellaris anterior.
To the intermediate brain:
4) lateral spinothalamic tract , tractus spinothalamicus lateralis is adjacent on the medial side to the tractus spinocerebellaris anterior, immediately behind the tractus spinotectalis. It conducts temperature irritations in the dorsal part of the tract, and pain in the ventral part.
B. Descending.
From the cerebral cortex:
1) lateral cortical-spinal (pyramidal) path , tractus orticospinalis (pyramidalis) lateralis. This tract is a conscious efferent motor path.
From the middle brain:
2) red nuclear-spinal tract tractus rubrospinalis. It is an unconscious efferent motor pathway that maintains skeletal muscle tone (posture) and performs complex automated movements (running, walking).
From the hindbrain:
3) olivo-spinal tract , tractus oIivospinalis, lies ventral to tractus spinocerebellaris anterior, near the anterior cord.
4) vestibulocerebral tract , tractus vestibulospinalis, is formed by the axons of the vestibular nuclei of the bridge and provides a redistribution of muscle tone in response to a change in body position in space.
Anterior cords contains descending paths.
From the cerebral cortex:
1) anterior cortical-spinal (pyramidal) path , tractus corticospinalis (pyramidalis) anterior, constitutes a common pyramidal system with the lateral pyramidal bundle.
From the midbrain:
2) tegmental-spinal tract, tractus testospinalis, lies medial to the pyramidal bundle, limiting the fissura mediana anterior. Thanks to him, reflex protective movements are carried out with visual and auditory irritations - the visual-auditory reflex tract.
From various nuclei of the medulla oblongata, related to balance and coordination of movements, namely:
3) from the nuclei of the vestibular nerve - tractus vestibulospinalis - lies on the border of the anterior and lateral cords;
4) from formatio reticularis - tractus reticulospinalis anterior, lies in the middle part of the anterior cord;
5) the bundles themselves, fasciculi proprii, are directly adjacent to the gray matter and belong to the own apparatus of the spinal cord.
6) tractus spinothalamicus anterior s. ventralis, is the way of conducting impulses of touch, touch (tactile sensitivity).
LECTURE #15
ANATOMY AND PHYSIOLOGY OF THE SPINAL CORD
The spinal cord (medulla spinalis) is a complex of the nucleus of the gray matter and the nerve fibers of the white matter, forming 31 pairs of segments. The spinal cord is about 43-45 cm long, about 1 cm in diameter, and weighs about 30-32 g. Each segment includes a corresponding sensory root that enters from the dorsal side and a motor (motor) root that exits from the ventral side.
The spinal cord (SC) is located in the spinal canal from C1 to L2, surrounded by membranes, between which cerebrospinal fluid (CSF) circulates. From above, the SM is connected to the brain. In the lower part, the SM has a cerebral cone (conus medullaris), from which the final thread (filum terminale) begins, at the level of the 2nd coccygeal vertebra, attached to the dura mater. With flexion and extension of the spine, there is a slight displacement in the spinal canal.
The diameter of the SM along its length is uneven. At the level of C 4-7 and Th 1, as well as in the lumbar and sacral regions, there are thickenings ( cervical enlargement And lumbosacral thickening), which are determined by the quantitative content of gray matter nerve cells involved in the innervation of the upper and lower extremities.
The SM consists of two symmetrical halves (right and left), separated in front - deep anterior median fissure, and behind - deep posterior median fissure. On the right and left halves there are anterior and posterior lateral grooves, in which, respectively, motor and sensory roots are located. There are 124 roots in total: 62 anterior (motor) and 62 posterior (sensory). The anterior roots are the axons of the effector cells located in the spinal cord. The posterior roots are the central processes of pseudo-unipolar cells located in the spinal nodes.
The CM consists of 31 segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal). Segment - a section of the spinal cord located in the horizontal plane, anatomically and functionally associated with 4 roots of the spinal nerves. The segments are responsible for the innervation of the skin and muscles of the corresponding parts of the body: cervical - neck, upper limbs, diaphragm; chest - chest, back and abdomen; lumbar, sacral and coccygeal - lower torso and lower extremities. Innervation on the trunk is presented in the form of annular bands, on the extremities - longitudinal.
In the lower sections of the spine, the length of the roots of the spinal nerves (SNR) is greater than in the upper ones (in the lumbar and sacral - 3-12 cm, in the cervical 1-1.5 cm). The roots of the 10 lower segments of the spine (L 2-5, S 1-5, Co 1) are ponytail, located in the sac of the dura mater and containing 40 roots (20 anterior + 20 posterior).
On a transverse section, the CM consists of both gray matter located inside in the form of a butterfly and white matter surrounding it. Gray matter is a collection of nerve cells nerve fibers. White matter is represented by processes of nerve cells that form nerve fibers.
IN gray matter distinguish the following departments:
1) Hind horns.
They contain sensitive nuclei that receive information from the sensitive (receptor) cells of the spinal nodes, accumulate it and transmit it to the integration centers of the brain.
2) Front horns (wider).
3) Lateral horns.
They contain vegetative sympathetic nuclei that receive information from sensitive cells of the spinal nodes, analyze it and provide sympathetic innervation of the internal organs.
4) Intermediate zone.
It contains a large number of intercalary neurons (about 90% of all gray matter cells).
The white matter on the right and left sides is divided by the roots of the spinal nerves into 3 cords (posterior, lateral and anterior), in which bundles of nerve fibers pass - tracts that provide two-way communication between the nuclei of the spinal cord and certain centers of the brain. A tract is a collection of axons of neurons that are identical in function and ensure the conduction of nerve impulses in a strictly defined direction.
The paths going from the sensory nuclei of the SM to the nuclei of the brain are called ascending (afferent); going from the centers of the brain to the SM - descending (afferent).
SPINAL TRACTS
I . Posterior cord
At the level of the cervical and upper thoracic segments of the spinal cord, the posterior intermediate sulcus is divided into two bundles.
1. thin beam (face. gracillis, Gaulle beam)
It is formed from the central processes of the nerve cells of the spinal nodes (SMU), from Th 9 and below.
2. wedge-shaped bundle (face. cuneatus, Burdach beam)
It is located laterally than the previous one. It consists of processes of cells of the thoracic and cervical SMU. The fibers of the thin and wedge-shaped bundles end in the nuclei of the medulla oblongata and provide conscious proprioceptive sensitivity.
3. Beam for holding tactile feeling.
Located between the two previous ones. It starts from the nuclei of the posterior columns and ends in the thalamus.
II . Lateral cord
A. Ascending paths:
1. Posterior spinal tract (tr. spinocerebelaris posterior, the Flexig sheaf).
Conducts proprioceptive impulses
2. Anterior dorsal tract (tr. spinocerebelaris anterior, the Gowers beam).
Conducts proprioceptive impulses to the cerebellum. It is located anterior to the Flexig's bundle.
The anterior and posterior spinal tracts provide unconscious and proprioceptive sensation.
3. Lateral spinothalamic tract (tr. spinothalamicus lateralis)
It represents the fibers of the ascending pathway, which begin in the posterior column of the spinal cord, cross in the spinal cord and end in the thalamus. Provides pain, temperature, tactile sensitivity from the opposite side.
B. Descending paths:
1. Lateral cortical-spinal tract (lateral-pyramidal) -tr. corticospinalis.
Conducts motor impulses from the cerebral cortex to the anterior horns of the spinal cord. The fibers of this path are processes of giant pyramidal cells. Its fibers in each segment of the SM on their side form synapses with the motor cells of the anterior column. Provides conscious movement.
2. Red nuclear-spinal tract (tr. rubrospinalis)
It is a conductor of impulses of automatic (subconscious) control of movements and tone of skeletal muscles to the anterior horns of the spinal cord.
3. Olivo-spinal and vestibular-spinal tract (tr. olivospinalis et vestibulospinalis).
Responsible for coordinating movements and maintaining balance.
III . Anterior funiculus
1. Medial longitudinal bundle
Responsible for the combined rotation of the head and eyes.
2. tectospinal tract (tr. tectospinalis).
It 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. Provides response protective reactions to visual and auditory stimuli.
3. Reticular-spinal tract (tr. reticulospinalis).
Conducts impulses from the reticular formation of the brain to the motor nuclei of the anterior horns of the spinal cord. Provides a connection between the structures of the reticular formation. It is located in the central part of the anterior funiculus.
4. anterior corticospinal tract (tr. corticospinalis anterior).
It starts from the pyramidal cells of the anterior central gyrus of the cerebral cortex, reaches the spinal cord, where in each segment it passes to the opposite side. Responsible for conscious movements, conducting impulses of motor reactions from the cerebral cortex to the anterior horns of the spinal cord.
5. Anterior dorsal thalamic tract (tr. spinothalamicus ventralis).
It is located anterior to the reticular-spinal tract. Conducts impulses of tactile sensitivity (pressure and touch).
6. Rear longitudinal beam(fasciculus longitudinalis dorsalis).
It stretches from the brain stem to the upper segments of the spinal cord. The fibers of the bundle conduct nerve impulses that coordinate the work of the muscles of the eyeball and neck.
7. The vestibular tract (tractus vestibulospinalis).
It is located on the border of the anterior funiculus with the lateral one. Localized in the superficial layers of the white matter of the anterior funiculus of the spinal cord. 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 posterior cord contains sensory tracts, the lateral cord contains sensory and motor tracts, and the anterior cord contains predominantly motor tracts.
In functional terms, two apparatuses are distinguished in the SM: segmental and conductive.
SEGMENTAL APPARATUS OF THE SPINAL CORD
Designed to provide unconditional simple protective reflexes (pulling the hand when pricked, etc.). This device works on the principle of the simplest reflex arcs (that is, without the participation of the brain). At the same time, the first sensitive neurons are pseudounipolar SMU cells; the second - intercalary neurons of the SM; the third are the effector neurons of the anterior horns of the spinal cord, which send impulses to the muscles. In humans, all reflex acts are polysegmental (i.e., capturing several segments).
CONDUCTION APPARATUS OF THE SPINAL CORD
Designed for the implementation of complex reflexes involving nerve centers brain. Information enters the nuclei of the posterior horns of the spinal cord, where it accumulates and reaches the corresponding nerve centers of the brain through sensory pathways. After analysis in these centers, it is transmitted downstream to the motor cells of the anterior horns of the spinal cord and from them to the muscles.
second higher education "psychology" in MBA format
subject: Anatomy and evolution of the human nervous system.
Manual "Anatomy of the central nervous system"
6.2. Internal structure of the spinal cord
6.2.1. Gray matter of the spinal cord
6.2.2. white matter
6.3. reflex arcs of the spinal cord
6.4. Pathways of the spinal cord
6.1. general review 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 more rapid growth 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: “Does a child laugh at the sight of a toy… does a girl tremble at the first thought of love, does Newton create the laws of universal gravitation and write 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.
As part of the posterior horns, there are a large number of intercalary neurons (interneurons) with which it contacts most of axons coming from sensory neurons located in the spinal ganglia as part of the posterior roots. 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 chest and sacral departments 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 paths 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 paths 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