Cortical centers. Subcortical centers Subcortical auditory centers include

The midbrain (mesencephalon) is the upper part of the brain stem. The midbrain is divided into the dorsal part - the roof of the brain (tectum) and the ventral part - the legs of the brain (pedunculi cerebri). The cavity of the midbrain is represented by a narrow canal - the Sylvian aqueduct (aqueductus cerebri), which connects the III and IV cerebral ventricles.

The roof of the midbrain, or plate of the quadrigemina, is formed by two upper (colliculi superior) and two lower colliculi (colliculi inferior). From each pair of hillocks in the direction of the diencephalon, pathways depart - pairs of handles of the hillocks (branchii colliculus). The handles of the superior colliculus terminate in the lateral geniculate bodies, while those of the inferior colliculi terminate in the medial geniculate bodies of the diencephalon.

On the basis of the brain, in front of the bridge lie the legs of the brain - two symmetrical thick divergent rollers that abut against the cerebral hemispheres. Between the legs there is an interpeduncular fossa (fossa interpeduncularis), closed by a posterior perforated space (substantia perforata posterior). On the medial surface of each leg, fibers of the third pair emerge oculomotor nerve(III - n. oculomotorius). The fibers of the IV pair of the trochlear nerve (IV-n. trochlearis) depart from the dorsal surface of the midbrain. Both nerves of the midbrain are motor.

On a transverse section of the midbrain, three sections are distinguished:

1) the roof of the midbrain (tectum mesencephali);

2) tire (tegmentum mesencephali);

3) the base of the legs of the brain (basis pedunculi cerebralis).

The outer surface of the roof of the midbrain is covered with a thin layer of white matter, passing into the knobs of the mounds.

Under this layer are the nuclei of the upper (nucleus colliculi superioris) and lower (nucleus colliculi inferioris) tubercles of the quadrigemina. The nuclei of the superior tubercles have a layered structure. Afferent fibers come to them from the optic tract, from the spinal cord along the spinothectal pathways, as well as collaterals from the lateral and medial loops. Efferent fibers depart to the motor nuclei of the brainstem and spinal cord along the tectobulbar and tectospinal tracts. The upper handles of the anterior tubercles are connected with the lateral geniculate bodies. In the nuclei of the lower tubercles, part of the fibers of the lateral loop ends. With efferent fibers, they are intertwined with the medial geniculate bodies (along the lower handles), as well as with spinal cord and the brain stem (along the tectospinal and tectobulbar tracts).

32. Question. Primary visual and auditory centers located in the midbrain.

The superior colliculus is the subcortical visual center, while the inferior colliculus serves as a switching point for the auditory pathways and plays the role of the auditory subcortical center. In the tegmentum of the midbrain there are red nuclei (nucleus ruber), which give rise to the rubrospinal path. In the red nuclei, the fibers of the upper legs of the cerebellum end. Around the aqueduct of Sylvius is the central gray matter (substantia grisea centralis). It contains the nuclei of the reticular formation of the midbrain, which receive collaterals from the ascending and descending paths passing here, and direct their long axons to other brain structures and to the cerebral cortex. The nuclei of the trochlear nerve (IV pair) lie in the central part of the gray matter, directly at the aqueduct of Sylvius, at the level of the inferior tubercles of the quadrigemina. Under the bottom of the water supply, at the level of the upper tubercles of the quadrigemina, are the nuclei of the oculomotor nerves (III pair). Lateral and superior to the red nuclei are layers of medial loops extending from the pontine tire. Between the tire and the base of the legs is a nucleus, consisting of cells rich in melanin - a black substance (substantia nigra).

The base of the legs of the brain is devoid of nuclei and is formed by the cortical-spinal, cortical-bridge pathways descending from the cerebral cortex.

The midbrain is the primary visual and auditory center, carrying out quick reflex reactions (defensive and orienting). In addition, red nuclei and substantia nigra are nuclei that control muscle tone and movement.

126. Cell structure retinas of the eye. The path of light in the retina. Pathways of the visual analyzer. Subcortical centers of vision (specific and nonspecific). Cortical center of vision

The retina has three radially arranged layers of nerve cells and two layers of synapses.

Ganglion neurons lie in the very depths of the retina, while photosensitive cells (rod and cone cells) are the most distant from the center, that is, the retina is the so-called inverted organ. Because of this position, light must penetrate all layers of the retina before it can fall on the photosensitive elements and induce the physiological process of phototransduction. However, it cannot pass through the epithelium or choroid, which are opaque.

When looking at blue light, leukocytes passing through the capillaries located in front of the photoreceptors can be perceived as small bright moving dots. This phenomenon is known as the blue field entopic phenomenon (or the Shearer phenomenon).

In addition to photoreceptor and ganglionic neurons, there are also bipolar nerve cells in the retina, which, located between the first and second ones, make contacts between them, as well as horizontal and amacrine cells that make horizontal connections in the retina.

Between the layer of ganglion cells and the layer of rods and cones are two layers of plexuses nerve fibers with many synaptic contacts. These are the outer plexiform (weave-like) layer and the inner plexiform layer. In the first, contacts are made between rods and cones and vertically oriented bipolar cells, in the second, the signal switches from bipolar to ganglion neurons, as well as to amacrine cells in the vertical and horizontal direction.

Thus, the outer nuclear layer of the retina contains the bodies of photosensory cells, the inner nuclear layer contains the bodies of bipolar, horizontal and amacrine cells, and the ganglionic layer contains ganglion cells, as well as a small number of translocated amacrine cells. All layers of the retina are permeated with Müller's radial glial cells.

The outer limiting membrane is formed from synaptic complexes located between the photoreceptor and outer ganglionic layers. The layer of nerve fibers is formed from the axons of ganglion cells. The inner limiting membrane is formed from the basement membranes of Müllerian cells, as well as the endings of their processes. Deprived of Schwann sheaths, the axons of ganglion cells, reaching the inner border of the retina, turn at a right angle and go to the place where the optic nerve is formed.

Each human retina contains about 6-7 million cones and 110-125 million rods. These photosensitive cells are unevenly distributed. The central part of the retina contains more cones, the peripheral part contains more rods. In the central part of the spot in the region of the fovea, the cones are minimal in size and mosaically ordered in the form of compact hexagonal structures.

Conducting path of the visual analyzer provides the conduction of nerve impulses from the retina to the cortical centers of the hemispheres of the diseased brain and is a complex chain of neurons connected to each other by means of synapses.

Heading towards the retina, the light beam passes through the light-refracting media of the eyeball (cornea, aqueous humor of the anterior and posterior chambers of the eye, lens, vitreous body) and is perceived by photoreceptor cells, whose bodies lie in the outer nuclear layer, in particular, their endings - receptors (rods and cones). Thus, the photoreceptor cells of the retina are the first neurons.

It should be noted that due to the refractive media of the eyeball, the light beam is concentrated in the area of ​​the place of greatest visual acuity - the retinal spot with its central fovea. In the fovea, only cone-shaped visual cells are concentrated, with which the perception of color is associated. There are 5-7 million of them in the retina. Cone-shaped optic cells are elements of daytime vision, so colors in the semi-darkness are perceived by them very weakly.

Rod-shaped visual cells are specialized for seeing objects at dusk. In the human retina, there are a total of about 75-150 million of these cells.

Light reaching the deep layers of the retina causes photochemical reactions due to visual pigments. The energy of light stimulation is converted by the photoreceptors of the retina ( rod-shaped and cone-shaped visual cells) into nerve impulses that rush to the second neurons located here in the retina.

The second neurons are represented by bipolar cells that make up the inner nuclear layer. Each bipolar neurocyte, with the help of its processes-dendrites, contacts simultaneously with several photoreceptor neurons.

in the ganglionic layer of the retina bodies of third neurons. These are large ganglionic (multipolar) cells. Usually one ganglion cell ( ganglionic neurocyte) contacts several bipolar cells. Axons of ganglion cells, converging, form the trunk of the optic nerve.

The exit point of the optic nerve from the retina is represented by the optic disc (blind spot). It does not contain photoreceptors.

Leaving the orbit, the optic nerve enters the cranial cavity through the optic canal and here forms a decussation at the base of the brain, and only the medial group of fibers following from the inner parts of the retina intersects, and the fibers from the outer parts of the retina do not intersect.

Thus, each hemisphere receives impulses simultaneously from the right and left eyes. All this ensures synchronization of movements. eyeballs and binocular vision, while amphibians and reptiles have autonomous eye movements, vision is monocular, which is associated with a complete decussation of the optic nerve fibers.

The section of the visual pathway from the retina to the optic chiasm is called optic nerve, after the cross - optic tract.

Each optic tract contains nerve fibers from the same halves of the retina of both eyes. So, the right optic tract - from the right half of the right eye (the fibers in the optic chiasm do not cross) and from the right half of the left eye (the fibers completely pass to the opposite side in the optic chiasm). Left optic tract- from the left half of the left eye (fibers crossed) and from the left half of the right eye (fibers completely crossed).

At the outer edge of the brain stem, the optic tract divides into three bundles heading towards subcortical centers of vision. Most of these fibers end on the cells of the lateral geniculate body, a smaller part - on the cells of the thalamus cushion and a small part related to the pupillary reflex - in the upper mounds of the roof of the midbrain. In these formations lie the bodies of the fourth neurons.

Axons of the fourth neurons, whose bodies are located in the lateral geniculate body and the pillow of the thalamus, pass in the form of a compact bundle through the posterior part of the posterior leg of the internal capsule, then, scattering like a fan, form visual radiance (Graziole's bundle *) and reach the cortical nucleus of the visual analyzer, which lies on the medial surface of the occipital lobes on the sides of the spur groove.

* Grantiolet Louis (1815-1885)- French physician, anatomist and physiologist. He worked in Paris, from 1853. taught anatomy at the University of Paris. since 1862 -Professor of zoology there. He studied comparative anatomy, anthropology, and psychology. Known for his work on the anatomy of the brain. He described a bundle of nerve fibers in the cerebrum, extending from the lateral geniculate body and the thalamic cushion to the visual center in the occipital cortex.

One of the divisions of the large brain is its smallest part - midbrain(mesencephalon), presented in the form of four "knolls", in which the nuclei are enclosed, performing the function of the centers of vision and hearing, the conductor of their signals. The "mounds" of the mesencephalon are a key part in the processing of information perceived by the senses.

What is the midbrain

Between the bridge and the diencephalon is gray matter, about 2 cm long and 3 cm wide, which is the second upper (superius) visual wire center. The nuclei of the medial auditory analyzer are also located there, which stood out, became a separate structure already in ancient people and is necessary for better transmission of signals from the sense organs to the final auditory centers.

Location

The nuclei of the mesencephalon, the pons and the medulla oblongata constitute the most important structure - the brainstem, which is a continuation of the spinal cord. The stem part was located in the canal of the first, second cervical vertebrae and partially in the occipital fossa. The complex of neurons is sometimes considered not as a separate independent part, but as a kind of longitudinal separating layer or tubercle of the medulla between the pons and diencephalon.

The structure of the midbrain

Conducting pathways pass through the stem part, connecting the cerebral cortex with the neurons of the spinal cord and the stem, in which they secrete:

• subcortical primary centers of the visual analyzer;
• subcortical primary centers of the auditory analyzer;
• all pathways connecting the nuclei of the cerebral hemispheres with the spinal cord;
• complexes (bundles) of white matter, providing direct interaction of all parts of the brain.

Based on this, the midbrain (mesencephalon) consists of two main parts: the tire (or roof), which contains the primary subcortical centers of hearing and vision, the legs of the brain with the interpeduncular space, representing the pathways. The most important component is the Sylvian aqueduct - a canal connecting the cavity of the third ventricle with the sinus of the fourth.

The aqueduct surrounds the gray and white central substance on all sides. The gray matter contains the reticular formation, nuclei cranial nerves. At the point where the aqueduct passes into the fourth ventricle, the medullary sail (in Latin, velum medullare) is formed. On the side sections of the Sylvius, the aqueduct looks like a triangle or a narrow slit and acts as an indicative element that helps to mark the location of the cerebral regions on x-rays.

Roof

The plate of the quadrigemina or the roof of the midbrain consists of two pairs of tubercles - upper and lower. Between them lies a large gap - the subpineal triangle. From all tubercles in the direction to the neurons of the cerebral hemispheres, bundles of fibers or cranked bodies depart. The first pair of hillocks are the primary visual centers, and the second pair are the primary auditory centers.

legs

Two thick strands, originating from under the pons, are called legs. They have several groups nerve cells sensory assignment together with motor neurons. In the medulla, formations of black and red color are isolated, which regulate arbitrary, involuntary movements of the fibers of striated muscle tissue.

Red cores

A structure that directly regulates the coordination of all voluntary movements of a person along with cerebellar neurons. The red nuclei consist of two parts: a small cell, which is the basis of the pathways, and a large cell, which forms the basis of the nuclei. Located in the upper tire next to the substantia nigra, they represent the main pyramidal centers of motor activity - the main part of the brain that controls all conscious and reflex movements of the human body.

black substance

The location of the black substance in the form of a crescent is between the tire and the legs. The substance contains a lot of melanin pigment, which gives the substance dark color. The substance belongs to the extrapyramidal propulsion system, regulates predominantly muscle tone and how automatic movements will be performed. The peculiarity of the medulla is that if black matter for some reason does not fulfill its function, then it is taken over by the red nuclei of the midbrain.

midbrain functions

For a long time, the network of nuclei was attributed to only one purpose in anatomy - the separation of the trunk and the cerebral hemispheres. In the course of further research, it became clear that they perform almost all the functions inherent in highly differentiated nervous tissue, they are the point of intersection of most of the sensory nerve pathways. The following functions of the human midbrain are distinguished:

1. Regulation of the physiology of the motor response to a strong external stimulus (pain, bright light, noise).
2. The function of binocular vision is to provide the ability to see a clear image simultaneously with both eyes.
3. The reaction in the organs of vision, which is of a vegetative nature, is manifested by accommodation.
4. Reflexes of the midbrain, providing a simultaneous turn of the eyes and head to an external stimulus of any strength.
5. Center for brief processing of the primary sensory, sensitive signal (vision, hearing, smell, touch) and its further direction to the main centers of the analyzers).
6. Adjustment of conscious and reflex skeletal muscle tone, allowing voluntary muscle contractions.

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Peripheral auditory system

Central part of the auditory system.

Features of the development of the organ of hearing in children

1. Hearing is a function of the body that provides the perception of sound vibrations in a particular habitat. In humans, this function is realized by a combination of mechanical, receptor and central nervous structures that form the auditory analyzer, or auditory sensory system.

auditory sensory system- a set of peripheral and cerebral nervous structures that provide the perception of sound vibrations. The auditory sensory system consists of peripheral and central sections.

Peripheral department includes the outer, middle and inner ear.

Central department represented by subcortical and cortical centers of hearing.

At different levels of evolutionary development and close connection with the characteristics of the habitat - aquatic, terrestrial, air - various forms of organization of the auditory system have developed with different functional capabilities for the perception of certain characteristics of sound signals.

So, back to the peripheral part of the auditory system.

Outer ear.

The outer ear is represented by the auricle and outer ear canal. Auricle It is made up of cartilage covered with skin. It passes directly into the external auditory meatus. Anterior to the external auditory meatus is a cartilaginous protrusion - the tragus. Ear lobe - lower part auricle, it consists of soft tissue and does not contain cartilage. External acoustical pass - in an adult, it has a length of 2.5-3.0 cm. Its initial part consists of cartilaginous tissue. The large (inner) part of the external auditory canal, the bony tube, is part of the temporal bone of the skull. The external auditory meatus forms a bend at the junction of the cartilaginous part with the bone. Throughout the external auditory canal is covered with skin, in which there are sebaceous and sulfuric glands that secrete the ear, a waxy protective substance. Despite their considerable size, the external structures of the human ear play a relatively small role in the processes of sound perception. Functions of the outer ear (pinna, external auditory canal and outer side eardrum) are reduced to ensuring directional reception of sound waves. The auricles are a mouthpiece and contribute to the concentration of sounds coming from different parts of space. Parts of the outer ear have a protective function. They protect the eardrum from mechanical and thermal influences, provide a constant temperature and humidity in this area, regardless of fluctuations in temperature and humidity in the external environment, thereby maintaining the stability of the elastic properties of the eardrum. The production of earwax protects against insects.

Eardrum. The external auditory canal ends at the tympanic membrane, which transmits air vibrations in the outer ear through the ossicular system of the middle ear. The tympanic membrane, whose area is 66-70mm2, is the boundary between the outer and middle ear. It has the shape of a cone with a top directed into the cavity of the middle ear, and is located at an angle of 45-50 degrees from the external passage. From the side of the external auditory canal, the tympanic membrane is covered with a thin layer of skin, the epidermis. From the side of the middle ear, it is covered with a mucous membrane, like the entire shell of the middle ear.

Most of the tympanic membrane is inserted into the bony groove in the depth of the ear canal and is called stretched. The smaller part, the anterosuperior, is attached where the bony groove breaks, is the relaxed part, or shrapnel membrane. The middle part of the stretched tympanic membrane consists of radial and circular fibrous fibers, which give it special strength. There is no fibrous layer in the shrapnel membrane.

From the side of the external ear, the tympanic membrane looks like a shiny gray oval plate; in the upper anterior part, a protrusion is visible - the place of attachment of the short process of the malleus - the bone of the middle ear. The handle of the malleus is fixed in the center of the tympanic membrane. This part, drawn into the middle ear, is called the navel of the eardrum. The main function of the tympanic membrane is the transmission of sound vibrations in the external auditory canal to the ossicular system. The eardrum performs a protective function, because thanks to the fibrous layer it has a special strength and can withstand air pressure up to two atmospheres.

Middle ear.

The middle ear consists of air cavities in the thickness of the pyramid of the temporal bone and includes:

- tympanic cavity

- auditory (Eustachian) tube

-mastoid

tympanic cavity, the central part of the middle ear, is a narrow irregular pyramid with a volume of about 1 cm. About 10 drops of liquid or a blackcurrant berry are placed in it. Six walls are clearly visible in the tympanic cavity:

External tympanic membrane

Internal - separates the tympanic cavity from the inner ear

Upper - separates the tympanic cavity from the cranial cavity

Inferior - borders on a large blood vessel - the bulb of the jugular vein

Anterior - in its lower part there is an opening leading to the Eustachian tube

Posterior - there is an opening in it connecting the tympanic cavity with the mastoid cavern

In the inner wall there are two openings-windows: an oval, or vestibule window (3-4 mm in diameter), and a round, or cochlear window (1-2 mm in diameter). The base of the stirrup is inserted into the oval window, attached by means of an annular ligament. The round window is covered with an elastic film called the secondary tympanic membrane. In the thickness of the inner and rear walls there is a channel facial nerve, therefore, with a disease of the middle ear, it can be involved in the inflammatory process.

The tympanic cavity is usually divided into three sections: upper, middle and lower.

In the tympanic cavity on thin ligaments, the auditory ossicles are movably fixed: hammer, anvil and stirrup. The sizes of the bones are calculated in millimeters. The smallest of them, the stirrup, weighs 2.5mg, its height is 4mm, its length is 3mm, and its width is 1.4mm.

The malleus has a head, a handle and two processes (short and long). The anvil is presented in the form of a body and two processes (long and short). The stirrup consists of two legs, a head and a base.

Vibrations of the tympanic membrane set in motion a hammer, the handle of which is attached to the navel of the tympanic membrane. The movements of the malleus are transmitted to the anvil and further to the final bone in this chain, the stirrup. The base of the stirrup (movable plate) is reinforced with an annular ligament in the oval cochlear window leading to the inner ear. The sound pressure at the entrance to the cochlea, due to the transfer function of the auditory ossicles, is amplified by 20 times. Such amplification has a large functional role, since the fluid of the inner ear has a much greater acoustic resistance than air.

In addition to the transfer function, the ossicular system plays a protective role: at high stimulus intensities, the nature of the movement of the ossicles changes, which ensures a change in the volume of fluids moved in the inner ear and protects the auditory system from overload. Violation of the activity of the auditory ossicles does not lead to total loss hearing. Due to the transmission of sound vibrations to the round window of the cochlea and bone conduction auditory sensitivity is preserved.

The tension of the tympanic membrane and the ossicular chain is provided by two muscles: tympanic(tympanic), stretching the eardrum and attached to the handle of the malleus, and stapedial(stirrup), attached to the head of the stirrup. The function of these muscles is that, by contracting, they change the amplitude of oscillations of the tympanic membrane and bones and thereby affect the transmission coefficient of sound pressure to the inner ear. They maintain the tone of the tympanic membrane and ensure the accommodation of the sound-conducting apparatus to stimuli of different intensity and frequency. With the contraction of the muscle stretching the eardrum, auditory sensitivity increases, i.e. anxiety occurs, especially with unexpected sounds. Contractions of the tympanic and stapedius muscles occur at sound intensities of more than 90 dB and have a protective function. The latent period of muscle contraction is too long to protect the ear from exposure to sharp sudden sounds, but with prolonged exposure to prolonged strong noise, muscle contraction acquires an important protective role - adaptive.

Muscle contractions, especially those stretching the tympanic membrane, also occur under the action of a new acoustic stimulus, during swallowing, chewing and yawning, during one's own speech activity. This indicates that the muscles of the middle ear are involved in not only the protective acoustic reflex, but also in the orientation response and feedback from the speech system to the auditory input. So, when a person speaks or sings, the muscles of the middle ear contract and the low-frequency sounds of the voice are suppressed, while the high-frequency sounds pass through the middle ear without distortion.

If the muscles of the middle ear are paralyzed due to a pathological process, the normal perception of loud sounds is disturbed, and the risk of acoustic injury increases. Thus, the muscles of the middle ear are a protective and adaptive active mechanism for regulating the intensity of an external stimulus and increasing the noise immunity of hearing.

Auditory (Eustachian) tube- connects the tympanic cavity of the middle ear with the nasopharynx. It is a narrow canal 3.5 cm long. The Eustachian tube is lined with ciliated epithelium, the hairs of which move towards the pharynx. The function of the Eustachian tube is to equalize the pressure in the middle ear with the pressure of the outside air. The walls of the Eustachian tube from the side of the nasopharynx are usually in contact with each other, but when swallowing they diverge as a result of contraction of the pharyngeal muscles. In this case, air from the nasopharynx passes into the tympanic cavity, and the pressure in the middle ear cavity is equalized with atmospheric pressure. This is especially important when there are sudden pressure drops near the eardrum (during high-speed ascent or descent in an elevator, airplane, etc.). Under these conditions, the Eustachian tube provides equalization of pressure on both sides of the eardrum, which relieves unpleasant and pain arising from sudden changes in pressure in the external environment.

mastoid process - temporal bone, located behind the auricle. In the thickness of the mastoid process there are many interconnected air cavities. The largest cavity - a cave (antrum) - communicates with tympanic cavity middle ear through a hole in its back wall. Both cavities have great importance in providing the resonant properties of the middle ear.

The inner ear is the canal system of the temporal bone with auditory and vestibular receptors located in it sensory systems. The relationship of the structures of the inner ear is complex, which justifies its name - the labyrinth. Distinguish bony and membranous labyrinths. The bony labyrinth is like a case for the membranous labyrinth. The membranous labyrinth is filled with endolymph fluid, and the space between the membranous labyrinth and bone fluid is perilymph. The inner ear consists from the vestibule, semicircular canals and cochlea.

vestibule, the central part of the labyrinth, represented by round and oval membranous sacs. The round sac communicates with the cochlea, the oval sac communicates with the semicircular canals.

Semicircular canals- upper, rear and outer are located in three mutually perpendicular planes. One of the ends of each channel is extended and is called ampoule. The vestibule and semicircular canals belong to the peripheral part of the vestibular (spatial) analyzer, or the organ of balance. In the sacs of the vestibule, the receptor of the vestibular analyzer is the otolith apparatus. The otolithic receptor consists of hair and supporting cells. Cell hairs are covered with an otolithic membrane, which includes hexagonal otolith crystals formed by calcium and magnesium salts. In the semicircular canals, the receptor of the organ of balance consists of hair (ciliary) and supporting cells, which form a special comb in the ampulla of the canals.

Snail- bone structure of the inner ear that performs the function of sound reception. The cochlea is twisted in the form of a spiral (bone labyrinth). The spiral forms 2.5-2.75 whorls, begins with a wide base and ends with a narrowed apex. The total length of the cochlear canal is approximately 35 mm. The central bone rod around which the coil of the cochlea is twisted is called the spindle (modiolus).

The organ of Corti is located in the cochlear duct. Its main functional part is the auditory cells, which end in sensory hairs and are therefore called hair cells.

The role of the cochlea in sound perception and hence:

The cochlea as a receptor apparatus converts the acoustic energy of sound vibrations into the excitation energy of nerve fibers

1 stage of frequency analysis of the acting sound is carried out in the cochlea

That. produced in the snail frequency-temporal spatial analysis of sound.

The peripheral section of the auditory analyzer is connected to the central, or cortical, end by nerve pathways consisting of four segments, or neurons.

2 question. The central end of the auditory analyzer is located in the cortex of the upper temporal lobe of each of the cerebral hemispheres (in auditory area bark). Especially importance in the perception of sound stimuli, they have transverse temporal gyrus, or the so-called Geschl gyrus. In the medulla oblongata, there is a partial intersection of nerve fibers connecting the peripheral section of the auditory analyzer with its central section. Thus, the cortical hearing center of one hemisphere is associated with peripheral receptors (organs of Corti) on both sides.

Consider the classical auditory pathway. This ascending specific path consists of several successive levels. (More at the seminar and at neuropathology)

1. Cochlear spiral ganglion

2. Cochlear nuclei medulla oblongata

3. Superior olive of the medulla oblongata

4. inferior tubercles of the quadrigemina of the midbrain

5. medial geniculate bodies of the thalamus

6. auditory fields of the temporal cortex.

In addition to the classical pathway, additional ascending auditory pathways have been found.

The projection center of hearing, or the core of the auditory analyzer. Located in the middle third of the superior temporal gyrus (field 22), it is predominantly on the surface of the gyrus facing the insula. In this center, the fibers of the auditory pathway terminate, originating from the neurons of the medial geniculate body (subcortical center of hearing) of its own and predominantly opposite sides. Ultimately, the fibers of the auditory pathway pass as part of the auditory radiance, radiatio acustica.

With the defeat of the projection center of hearing on one side, there is a decrease in hearing in both ears, and on the opposite side of the lesion, hearing is reduced to a greater extent. Complete deafness is observed only with bilateral damage to the cortical projection analyzers of hearing.

The projection center of vision, or the core of the visual analyzer. This nucleus is localized on the medial surface of the occipital lobe, along the edges of the spur groove (field 17). It ends with the fibers of the visual pathway from its own and opposite sides, originating from the neurons of the lateral geniculate body (subcortical center of vision). The neurons of field 17 perceive light stimuli, therefore, the retina is projected on this field.

Unilateral damage to the projection center of vision within field 17 is accompanied by partial blindness in both eyes, but in different parts of the retina. Complete blindness occurs only with a bilateral defeat of field 17.

The projection center of smell, or the core of the olfactory analyzer. It is located on the medial surface of the temporal lobe in the cortex of the parahippocampal gyrus and in the hook (limbic region - fields A, E). Here the fibers of the olfactory pathway end on their own and opposite sides, originating from the neurons of the olfactory triangle. With a unilateral lesion of the projection center of smell, a decrease in smell and olfactory hallucinations are noted.

The projection center of taste, or the core of the taste analyzer. It is located in the same place as the projection center of smell, that is, in the limbic region of the brain. In the projection center of taste, the fibers of the taste pathway of their own and opposite sides, originating from the neurons of the basal nuclei of the thalamus, end.

When the limbic region is affected, there are disorders of taste, smell, and hallucinations appear.

Projection center of sensitivity from internal organs, or anavisceroception lyzer. Located in lower third postcentral and precentral gyri (field 43). The cortical part of the visceroception analyzer receives afferent impulses from the smooth muscles and glands of the internal organs. In the cortex of field 43, the fibers of the interoceptive pathway end, originating from the neurons of the ventrolateral nucleus of the thalamus, into which information enters through the nuclear-thalamic tract, tr. nucleothalamicus. In the projection center of visceroception, mainly pain sensations and afferent impulses from smooth muscles are analyzed.

Projection center of vestibular functions. The vestibular analyzer undoubtedly has its representation in the cerebral cortex, but information about its localization is ambiguous. It is generally accepted that

the projection center of vestibular functions is located on the dorsal surface of the temporal lobe in the region of the middle and inferior temporal gyri (fields 20, 21). The adjacent sections of the parietal and frontal lobes also have a certain relation to the vestibular analyzer. In the cortex of the projection center of vestibular functions, fibers originating from the neurons of the central nuclei of the thalamus end. Lesions of these cortical centers are manifested by spontaneous dizziness, a feeling of instability, a feeling of sinking, a feeling of movement of surrounding objects and deformation of their contours.

Concluding the consideration of the projection centers, it should be noted that the cortical analyzers of general sensitivity receive afferent information from the opposite side of the body, so the damage to the centers is accompanied by disorders of certain types of sensitivity only on the opposite side of the body. Cortical analyzers of special types of sensitivity (auditory, visual, olfactory, gustatory, vestibular) are associated with the receptors of the corresponding organs of their own and opposite sides, therefore, the complete loss of the functions of these analyzers is observed only when the corresponding zones of the cerebral cortex are damaged on both sides.

Associative nerve centers. These centers are formed later than the projection ones, and the timing of corticalization, i.e. maturation of the cerebral cortex in these centers is not the same. Given the connection of associative centers with thought processes and verbal function, it is generally accepted that they develop in the cerebral cortex only in humans. Some researchers admit the existence of such centers in higher vertebrates. Consider the main associative centers.

The associative center of "stereognosia", or the core of the skin analyzer of bonds names of items on touch. This center is located in the superior parietal lobule (field 7). It is bilateral: in the right hemisphere - for the left hand, in the left - for the right. The center of "stereognosia" is associated with the projection center of general sensitivity (posterior central gyrus), from which nerve fibers conduct impulses of pain, temperature, tactile and proprioceptive sensitivity. The incoming impulses in the associative cortical center are analyzed and synthesized, resulting in the recognition of previously encountered objects. Throughout life, the center of "stereognosia" is constantly developing and improving. With damage to the upper parietal lobule, patients lose the ability to eyes closed create a common holistic view With object, that is, they cannot recognize this object by touch. Separate properties of objects, such as shape, volume, temperature, density, mass, are determined correctly.

The associative center of "praxia", or the analyzer of purposeful habits nyh movements. This center is located in the lower parietal lobule in \ the cortex of the supramarginal gyrus (field 40), in right-handers - in the left hemisphere of the large brain, in left-handers - in the right. In some people, the center of "praxia" is for-; mired in both hemispheres, such people equally own the right and left hands and are called ambidexes.

The center of "praxia" develops as a result of repeated repetition of complex purposeful actions. As a result of fixing temporary connections, habitual skills are formed, for example, work on a writing

typewriter, playing the piano, performing surgical procedures, etc. With the accumulation of life experience, the center of praxia is constantly being improved. The cortex in the region of the supramarginal gyrus has connections with the posterior and anterior central gyrus.

After the implementation of synthetic and analytical activities from the center of "praxia", information enters the anterior central gyrus to the pyramidal neurons.

The defeat of the center of "praxia" is manifested by apraxia, i.e., the loss of arbitrary, purposeful movements acquired by practice.

Associative center of vision, or analyzer of visual memory. This center is located on the dorsal surface of the occipital lobe (fields 18-19), in right-handers - in the left hemisphere, in left-handers - in the right. It provides memorization of objects by their shape, appearance, color. It is believed that field 18 neurons provide visual memory, and field 19 neurons provide orientation in an unusual environment. Fields 18 and 19 have numerous associative connections with other cortical centers, due to which integrative visual perception occurs. With damage to the center of visual memory (field 18), visual agnosia develops. Partial agnosia is more often observed (does not recognize acquaintances, his home, himself in the mirror). When field 19 is affected, a distorted perception of objects is noted, the patient does not recognize familiar objects, but he sees them, bypasses obstacles.

The human nervous system has specific centers. These are the centers of the second signaling system - centers that provide the ability to communicate between people through articulate human speech. Human speech can be reproduced in the form of the performance of articulate sounds ("articulation") and the image of written characters ("graphics"). Accordingly, associative speech centers are formed in the cerebral cortex (acoustic and optical centers of speech, the center of articulation and the graphic center of speech). The named associative speech centers are laid down near the corresponding projection centers. They develop in a certain sequence, starting from the first months after birth and can improve until old age. Let's consider the associative speech centers in the order of their formation in the brain.

The associative center of hearing, or the acoustic center of speech. This center is also called the Wernicke center, by the name of a German neurologist and psychiatrist, who first described in 1874 the symptoms of damage to the posterior third of the superior temporal gyrus, within which this center is located. On the neurons of this section of the cortex, nerve fibers originating from the neurons of the projection center of hearing (the middle third of the superior temporal gyrus) end. The associative hearing center begins to form in the second or third months after birth. As the center forms, the child begins to distinguish articulate speech among the surrounding sounds, first individual words, and then phrases and complex sentences.

With the defeat of the center of Wernicke, the patient develops sensory aphasia. This manifests itself in the form of a loss of the ability to understand one's own and other people's speech, although the patient hears well, reacts to sounds, but it seems to him that those around him speak an unfamiliar language. The lack of auditory control over one's own speech leads to a violation of the construction of sentences, speech becomes incomprehensible, saturated with meaningless words and sounds.

However, patients with sensory aphasia are extremely talkative. With the defeat of the center of Wernicke, since it is directly related to speech formation, not only the understanding of words suffers, but also their pronunciation.

Associative motor center of speech (speech motor), or center of speech articulation. This center is called Broca's Center, after the name of the French anatomist and surgeon, who in 1861 for the first time demonstrated at a meeting of the Paris Anthropological Society the brain of a patient with a lesion in the posterior third of the inferior frontal gyrus. The patient during his lifetime suffered from impaired articulation of speech.

The motor speech center is located in the posterior part of the inferior frontal gyrus (field 44) ​​in close proximity to the projection center of motor functions (precentral gyrus). The speech motor center begins to form in the third month after birth. It is one-sided - in right-handers it develops in the left hemisphere, in left-handers - in the right. Information from the motor speech center enters the precentral gyrus and further along the cortical-nuclear path - to the muscles of the tongue, larynx, pharynx, muscles of the head and neck.

With the defeat of the speech-motor center, motor aphasia (loss of speech) occurs. Speech in such patients is slowed down, difficult, scanned, incoherent, often characterized only by individual sounds. Patients understand the speech of others.

Associative optical center of speech, or visual analyzer of writingspoken language (center of the lexicon). This center is located in the angular gyrus of the inferior parietal lobule (field 39). For the first time this center was described in 1914 by Dezherin. The neurons of the optical center of speech receive visual impulses from the neurons of the projection center of vision (field 17). In the center of the "lexia" there is an analysis of visual information about letters, numbers, signs, the literal composition of words and understanding their meaning. The center is formed from the age of three, when the child begins to learn letters, numbers and evaluate their sound value.

With the defeat of the center of "lexia" comes alexia (reading disorder). The patient sees the letters, but does not understand their meaning and, therefore, cannot read the text.

Associative center of written signs, or motor analyzerwritten characters (center decanter). This center is located in the posterior part of the middle frontal gyrus (field 8) next to the precentral gyrus. The center of "graphics" begins to form in the fifth or sixth year of a child's life. This center receives information from the "praxia" center, designed to provide subtle, precise hand movements necessary for writing letters, numbers, for drawing. From the neurons of the "decanter" center, axons are sent to the middle part of the precentral gyrus. After switching, information is sent along the cortical-spinal tract to the muscles upper limb. When the center of "graphics" is damaged, the ability to write individual letters is lost, "agraphia" occurs. Thus, the speech centers have one-sided localization in the cortex of the cerebral hemispheres: in right-handers they are located in the left hemisphere, in left-handers - in the right. It should be noted that associative speech centers develop throughout life.

Associative center of combined rotation of the head and eyes (corticaleye center). This center is located in the middle frontal gyrus (field 9)

Rice. 53. Localization of functions in the cerebral cortex (VV Turygin, 1990). a - dorso-lateral surface; b - medial surface.

1 - associative center of the combined turn of the head and eyes in the opposite direction;

2 - center of graphics; 3 - projection center of motor functions; 4 - projection center

general sensitivity; 5 - speech motor center; 6 - projection center of visceroception;

7 - projection center of hearing; 8 - projection center of vestibular functions;

9 - associative center of hearing; 10 - center of praxia; 11 - center of stereognosy; 12 - the center of the lecture;

13 - associative center of vision; 14 - projection center of smell;

15 - projection center of taste; 16 - projection center of vision

anterior to the motor analyzer of written characters (center of graphics). It regulates the combined rotation of the head and eyes in the opposite direction due to impulses entering the projection center of motor functions (precentral gyrus) from the proprioceptors of the muscles of the eyeballs. In addition, this center receives impulses from the projection center of vision (the cortex in the region of the spur groove - field 17), originating from the neurons of the retina.

The localization of functions in the cerebral cortex is shown in Figure 53.