Cortical hearing centers. Functions of the central parts of hearing
In the medial geniculate body of the metathalamus, the fibers of the nuclei of the lateral (auditory) lemniscus end, therefore the medial geniculate body, together with the inferior colliculus of the midbrain roof, is the subcortical center of hearing.
The medial geniculate body lies in front of the handle of the inferior colliculus of the midbrain roof under the thalamic cushion. It is connected to the lower colliculus using the handle of the lower colliculus. The fibers of the nuclei of the lateral (auditory) lemniscus end in the medial geniculate body, therefore the medial geniculate body, together with the inferior colliculus of the midbrain roof, is the subcortical center of hearing.
The medial geniculate body, along with the lower colliculi of the midbrain roof plate (quadrigeminal), is the subcortical center of the auditory analyzer
Thalamus: specific nucleus
Central auditory system
The metathalamus is formed by the paired medial geniculate body and lateral geniculate body, lying behind each optic thalamus. The medial surfaces of both visual thalamus facing each other form the lateral walls of the cavity of the diencephalon - the third ventricle.
In the lateral part of the dorsal thalamus, there are two highly specialized thalamic nuclei, which represent the switching zones of the ascending fibers of the auditory system to the auditory cortex and the ascending visual fibers to the visual cortex. Since the nuclei are highly specialized and in humans are clearly expressed as independent mound-like structures, anatomists (R.D. Sinelnikov, M.R. Sapin) distinguish these nuclei into an independent section of the dorsal thalamus - the retrothalamic region (metathalamus).
The metathalamus thus includes two pairs of metathalamic geniculate bodies: the lateral geniculate body of the metathalamus (corpus geniculatum laterale) and the medial geniculate body of the metathalamus (corpus geniculatum mediale).
The lateral geniculate body is located lateral to the thalamic cushion. It is connected to the superior colliculus of the midbrain via the handle of the superior colliculus. Most of the lateral root of the optic tract ends in the lateral geniculate body (the other part ends in the pillow), therefore, together with the pillow and the superior colliculus of the roof of the midbrain, the lateral geniculate body is the subcortical center of vision.
The medial geniculate body lies in front of the handle of the inferior colliculus of the midbrain roof under the thalamic cushion. It is connected to the inferior colliculus of the midbrain roof using the handle of the inferior colliculus. The fibers of the nuclei of the lateral (auditory) lemniscus end in the medial geniculate body, therefore the medial geniculate body, together with the inferior colliculus of the midbrain roof, is the subcortical center of hearing.
15. COORDINATION OF MOVEMENTS. TYPES OF MOVEMENTS. DEVELOPMENT OF MOTOR SKILLS.
The term “coordination” comes from the Latin coordinatio - mutual ordering. Coordination of movements refers to the processes of coordinating the activity of the muscles of the body, aimed at the successful completion of a motor task.
For the central nervous system, the control object is the musculoskeletal system. The uniqueness of the musculoskeletal system lies in the fact that it consists of a large number of links, movably connected at joints that allow rotation of one link relative to another.
Human movements are very diverse, but all this diversity can be reduced to a small number of basic types of activity: ensuring posture and balance, locomotion (active movement in space over distances significantly exceeding the characteristic dimensions of the body) and voluntary movements.
Maintaining posture in humans is ensured by the same physical muscles that perform movement, and there are no specialized tonic muscles. During “postural” muscle activity, the force of their contraction is usually small, the mode is close to isometric indicators, and the duration of contraction is significant. The “postural” or postural mode of muscle work primarily involves low-threshold, slow, and fatigue-resistant motor units.
One of the main tasks of “postural” activity is maintaining the desired position of the body parts in the field of gravity (keeping the head from hanging, keeping the ankle joints from dorsiflexing when standing, etc.). “Postural” activity can also be aimed at fixing joints that do not participate in the movement being performed. In work activity, maintaining a pose is associated with overcoming external forces.
A typical example of a pose is a person standing. Maintaining balance while standing is possible if the projection of the body's center of gravity is within the support contour. Ensuring stability is achieved by the active work of many muscles of the trunk and legs, and the force developed by these muscles is small. The maximum tension when standing is developed by the muscles of the ankle joint, and the minimum tension is developed by the muscles of the knee and hip joints. In most muscles, activity is maintained at a more or less constant level. Other muscles are activated periodically. This activation is associated with small fluctuations in the body's center of gravity in both the sagittal and frontal planes that constantly occur during standing. The muscles of the lower leg counteract the deviations of the body, returning it to an upright position. Maintaining a posture is an active process that, like movement, involves feedback from receptors. Vision and the vestibular apparatus are involved in maintaining a vertical posture. Proprioception also plays an important role. Maintaining balance while standing is only a special case of “postural” activity.
Related to the concept of posture is the concept of muscle tone. The term “tone” has many meanings. At rest, muscle fibers have turgor, which determines their resistance to pressure and stretching. This constitutes that component of tone that is not associated with specific neural activation of the muscle causing its contraction. However, under natural conditions, most muscles are usually activated to some extent by the nervous system, in particular to maintain posture (“postural” tone). Another important component of tone is the reflex component, determined by the stretch reflex. In humans, it is detected by the resistance to muscle stretching during passive rotation of a limb link in the joint.
The most common form of human locomotion is walking. It refers to cyclic motor acts in which successive phases of movement are periodically repeated.
Running differs from walking in that the leg that is behind you pushes off the support before the other leg comes down on it. As a result, running has a period without support, a period of flight.
Voluntary movements in a broad sense can be called a variety of movements performed both in the process of work and in everyday life.
The motor skills that children learn are typically everyday activities such as tying shoelaces, using scissors, or performing jumping jacks. Mastering these skills allows the child to move freely, take care of himself and show creativity. Some of them try to master more complex skills, such as performing gymnastic exercises, playing the piano, and even horse riding.
Experts have long identified a number of essential conditions for motor learning. These are readiness, activity, attention, motivation of competence and feedback. Forming any new skill requires that the child be in a state of readiness. In order to benefit from the exercise, the child must have reached a certain level of development (due largely to maturation processes) and have a number of prior knowledge and skills. Despite the fact that it is quite difficult to determine when children reach this state of readiness, classic studies conducted in Russia and the USA allowed us to draw the following conclusion. If you begin to skill-teach a child new actions at the moment of his highest readiness, he will master them quickly, with minimal effort and without much stress. Children in this state want to learn, enjoy their studies and are wildly happy about their successes. Their behavior is the best indicator of whether they have reached a state of readiness; they themselves begin to imitate certain actions.
Activity is essential for motor development. Children won't learn to climb stairs if they don't try. They won't be able to throw the ball unless they practice it. If a child lives in cramped conditions, the development of his motor skills will be delayed. Children who are unable to fully demonstrate their activity when learning something (due to a lack of toys, places for examination, people they could imitate) may have difficulties in developing motor skills. On the other hand, those whose environments actively influence them and are varied have the necessary stimulation for learning. They copy the performance of certain actions, repeating them many times. Children love to pour water from one glass to another, which helps them understand the concepts of “full” and “empty”, “fast” and “slow”. This self-selected and regulated learning regimen is often more effective than an adult-programmed learning cycle.
Motor development occurs more efficiently through attention, which requires a certain level of wakefulness and engagement in the situation. But how can you encourage your child to be more attentive? Kids cannot simply be told what and how they need to do. For example, 2-3 year old children master physical skills more successfully if someone guides their actions. In order to teach a child any special movements of the arms and legs, it is useful to resort to games and exercises. This technique has shown that children aged 3 to 5 years are better able to concentrate their attention if they actively repeat someone else's actions. At the age of 6-7 years, they can already pay attention to verbal instructions and are able to follow them quite accurately, at least when they take part in activities that are familiar to them.
The subcortical centers are located above the diencephalon. Of these, the most important are the striatal bodies, which consist of two nuclei: the caudate and the lentiform. The caudate nucleus is adjacent to the optic thalamus. It is separated from the lenticular nucleus by a bundle of white nerve fibers - the internal capsule. The lenticular nucleus is divided into an outer part, the putamen, and an inner part, the globus pallidus.
The globus pallidus is the main motor center of the diencephalon. Its stimulation causes strong contractions of the muscles of the neck, arms, torso and legs, mainly on the opposite side. Overexcitation of the globus pallidus causes obsessive movements of the hands, mainly the fingers - athetosis and the whole body - chorea. Chorea, or involuntary dance, occurs in children from 6 to 15 years old. The globus pallidus inhibits the red nucleus along centrifugal fibers, suppressing contractile tone. Therefore, turning off the globus pallidus leads to general stiffness, a sharp increase in muscle tone, a mask-like face, and quiet monotonous speech. The globus pallidus refines the coordination of movements, participating in the performance of additional movements that contribute to the performance of the main ones, for example, in fixing joints, swinging arms when walking, etc., and coordinates motor reflexes with autonomic functions.
The caudate nucleus and the shell of the lentiform nucleus inhibit the globus pallidus along centrifugal fibers and stop the overproduction of movements (hyperkinesis) caused by its excitation. Therefore, their defeat causes hyperkinesis, athetosis and chorea. The caudate nucleus and putamen of the lentiform nucleus receive centripetal fibers from the optic thalamus and cerebellum, which ensures their participation in the functions of these parts of the nervous system.
The motor nuclei of the striatum, optic thalamus, diencephalon and hypothalamic region and the red nucleus are part of the extra-pyramidal system, which, with the leading role of the pyramidal system, is involved in the performance of complex congenital motor acts associated with the activity of internal organs (food, sexual reflexes etc.) and in changes in the position and movement of the body (work and sports movements, walking, running, etc.). In each hemisphere, the limbic, or marginal, lobe of the cerebral hemispheres is closely connected with the listed formations of the brain stem, which, like the cingulate gyrus, encircles the corpus callosum in front and goes around behind, passing into the seahorse gyrus (hippocampus). Together with the fornix and the amygdala nucleus, the limbic lobe makes up the limbic system.
The limbic system is connected to the reticular formation of the brain stem and causes changes in body functions characteristic of emotions, the leading role in the implementation of which belongs to the frontal lobes.
Read:
|
Conducting pathways and centers of the auditory analyzer.
The conduction path of the auditory analyzer ensures the conduction of nerve impulses from the sensory hair cells of the spiral (corti) organ to the auditory centers of the cerebral cortex.
The modern understanding of the activity of analyzers allows us to distinguish three main parts of the auditory analyzer:
· peripheral receptor compartment - cochlea with organ of Corti
· conducting pathways and centers of the cochlear system, including subcortical formations
· the part of the cerebral cortex that perceives and processes information.
The sound-receiving system is the inner ear. It contains the receptor apparatus of two analyzers: the vestibular (vestibule and semicircular canals) and the auditory, which includes the cochlea with the organ of Corti.
The inner ear (auris interna) is located in the pyramid of the temporal bone and is represented by the bony labyrinth and the membranous labyrinth enclosed within it. Between the bony and membranous labyrinths there is a perilymphatic space filled with fluid - perilymph. The membranous labyrinth is filled with fluid - endolymph.
The membranous labyrinth follows the course of the bony labyrinth, which consists of three parts:
1. the front part is the cochlea (cochlea);
2. middle part - vestibule (vestibulum);
3. posterior part - three semicircular canals.
The membranous cochlea contains the organ of hearing, the so-called. spiral (or Corti) organ. It perceives sound (acoustic) vibrations that are transmitted to it through the external auditory canal, tympanic membrane, auditory ossicles, oval window of the vestibule of the labyrinth, perilymph of the cochlea and endolymph of the membranous cochlea.
Vibrations of the tympanic membrane are transmitted along the chain of auditory ossicles to the oval window of the vestibule and here they initiate vibrations of the perilymph. The vibrations of the perilymph spread along the scala vestibular to the apex of the cochlea, pass into the scala tympani and descend down to the round window of the vestibule. In the absence of the round window, the stapes, due to the incompressibility of the fluid, could not set the perilymph in motion.
At the same time, vibrations of the perilymph (and endolymph) of the cochlea cause irritation of certain sensoroepithelial hair cells of the organ of Corti, which is perceived by the dendrites of the first neurons of the auditory analyzer.
Finally, let's turn to the key element of the hearing organ - the organ of Corti. It contains 2 types of cells: sensory hair epithelial cells and supporting epithelial cells. Supporting cells, in turn, are divided into 3 types: pillar cells, phalangeal and border cells.
Pillar cells are narrow cells located on the basilar plate in two rows - so that the rows at the top converge at an angle to each other, and an internal tunnel filled with endolymph is formed between the rows. The tunnel divides the cells of the spiral organ (both sensory and supporting) into internal and external. Phalangeal cells lie on the basilar plate on each side of the pillar cells. In this case, the internal phalangeal cells are arranged in 1 row, and the external ones - in 3-4 rows. On each such cell, as on a bed, there is a sensory cell. To hold the latter, phalangeal cells have thin finger-like processes (“phalanxes”).
Since the sensory cells are located on the phalangeal cells, therefore, in accordance with the number of the latter, the internal sensory cells are located in 1 row, and the external ones in 3-4 rows. There are two formations on the apical surface of sensory cells:
1. cuticle-film of glycoprotein nature;
2. special microvilli - stereocilia, which are combined into bundles, pierce the cuticle and contact the integumentary membrane.
The bases of sensory cells form synapses - with the dendrites of the first neurons of the auditory analyzer and with efferent nerve fibers. Efferent nerve fibers approach the organ of Corti from the olive (nucleus of the medulla oblongata) - the so-called. olivocochlear bundle. In this case, some of the efferent fibers end on sensory cells, and others end on afferent fibers extending from these cells (forming axodendritic synapses). Apparently, efferent fibers have an inhibitory effect, i.e. limit impulses coming from the organ of Corti. The mediators in the synapses they form are: acetylcholine, gamma-aminobutyric acid (GABA) and glycine.
Bodies first(afferent) neurons are located at the base of the spiral bone crest of the cochlea and form the so-called. spiral ganglion (ganglion spirale cochleae). The dendrites of these neurons approach the basilar membrane (losing the myelin sheath). Then some of them go to the inner hair cells, the other part passes through the tunnel and goes to the outer hair cells. The axons of the bipolar neurons of the spiral ganglion form the radix cochleare, which, as part of n. VIII (n. Vestibulocochlearis), exits the pyramid of the temporal bone through the internal auditory opening. In the region of the cerebellopontine angle, the nerve enters the brainstem directly behind the inferior cerebellar peduncle (pedunculus cerebellaris inferior). In the brain stem there are second neurons auditory nerve, represented by the ventral and dorsal cochlear nuclei of the bridge (nucleus cochlearis ventralis et nucleus cochlearis dorsalis) and nucleus olivaris cranialis.
Axons originating from the ventral cochlear nucleus move to the opposite side and participate in the formation of the trapezoidal body (corpus trapezoideum), located on the border between the base and the tyres, of the pons. Axons originating from the dorsal cochlear nucleus extend to the dorsal surface of the pons, forming the medullary (auditory) stripes of the fourth ventricle, which then pass as part of the trapezoidal body. In the trapezoidal body, the axons of the second neurons partially end on the neurocytes of the small nuclei of the trapezoidal body. The fibers of the trapezoid body form the bend-lateral (auditory) loop (Lemniscus lateralis), which consists of axons of the second and, partially, third neurons(nuclei of the trapezoid body) of the auditory pathway.
The auditory loop fibers are directed to subcortical centers: inferior colliculi of the midbrain, medial geniculate body, median nuclei of the thalamus ( 4 neurons):
· from the lower colliculi of the midbrain, information is carried out to the superior colliculi and further along the tr.tectosinalis - an extrapyramidal protective motor tract that provides a response to unexpected sound stimuli;
· from the median nuclei of the thalamus, impulses arrive at the medial nuclei, which are the subcortical sensitive center of the extrapyramidal system; this ensures redistribution of muscle tone in response to appropriate sound stimulation;
· from the nuclei of the medial geniculate bodies auditory information along tr. geniculotemporalis passes through the posterior leg of the internal capsule and then, in the form of radiatio acustica, is directed to the middle part of the superior temporal gyrus, the projection center of hearing.
The central end of the auditory analyzer is located in the cortex of the superior temporal lobe of each cerebral hemisphere (in the auditory cortex). The transverse temporal gyri, the so-called Heschl gyrus, are especially important in the perception of sound stimuli. In the medulla oblongata, a partial crossover of nerve fibers occurs, connecting the peripheral part of the auditory analyzer with its central part. Thus, the cortical hearing center of one hemisphere is connected with peripheral receptors (organs of Corti) on both sides. Conversely, each organ of Corti is connected to both cortical hearing centers (bilateral representation in the cerebral cortex). The cortical nucleus of the auditory analyzer perceives auditory stimulation mainly from the opposite side. Due to the incomplete decussation of the auditory pathways, unilateral damage to the lateral lemniscus, subcortical auditory center or cortical nucleus of the auditory analyzer may not be accompanied by a severe hearing disorder, only a decrease in hearing in both ears is noted. Also quite often there is a decrease in hearing due to neuritis (inflammation) of the vestibulocochlear nerve. Hearing loss can also occur as a result of selective irreversible damage to sensory hair cells when large doses of antibiotics that have an ototoxic effect are introduced into the body.
The core of the auditory analyzer of oral speech has a close connection with the cortical center of the auditory analyzer and is located, like the auditory analyzer, in the region of the superior temporal gyrus. This nucleus is located in the posterior parts of the superior temporal gyrus, on the side facing the external sulcus of the cerebral hemisphere. The function of the core is that a person can not only perceive and understand someone else’s speech, but also control his own.
The primary cortical field is surrounded by secondary projection fields in which auditory stimuli are analyzed, identified, and compared. They are also interpreted and recognized as noises, tones, melodies, vowels and consonants, words and sentences, in other words, symbols of speech. If these cortical areas are damaged in the dominant hemisphere, the ability to recognize sounds and understand speech is lost (sensory aphasia).
The functional significance of different parts of the auditory analyzer is different. The system of the eardrum, auditory ossicles and receptors of the organ of Corti forms the perceptive apparatus. At the level of the lower colliculi, reflex arcs are closed, providing motor responses to auditory stimuli. For example, a person usually turns his head towards the source of the sound. This reflex appears from early childhood. At a sharp unexpected sound, a person flinches. This is a variant of the “start reflex”, which closes at the level of the midbrain with the participation of the reticular formation. In the cortical sections of the auditory analyzer, complex processes of processing sound signals take place - isolating sound images, comparing them with signals stored in memory.
Thus, the auditory pathways are a set of nerve fibers that conduct nerve impulses from the cochlea to the auditory centers of the cerebral cortex, resulting in an auditory sensation. The time it takes for the auditory signal to travel from the outer ear to the auditory centers of the brain is about 10 milliseconds. The brain and the intermediate nodes of the auditory pathways extract not only information about the pitch and volume of the sound, but also other characteristics of the sound, for example, the time interval between the moments when the right and left ear picks up the sound - this is the basis of a person’s ability to determine the direction in which the sound is coming. In this case, the brain evaluates both the information received from each ear separately and combines all the information received into a single sensation. In order to correctly hear and understand sounds, coordinated work of the auditory analyzer and the brain is necessary. Thus, without exaggeration, we can say that a person hears not with his ears, but with his brain!
Auditory pathways and lower auditory centers - this is the conductive afferent (bringing) part of the auditory sensory system, conducting, distributing and transforming sensory excitation generated by auditory receptors to form reflex reactions of effectors and auditory images in the higher auditory centers of the cortex.
All auditory centers, starting from the cochlear nuclei and up to the cerebral cortex, are arranged tonotopically, i.e. receptors of the organ of Corti are projected into them onto strictly defined neurons. And, accordingly, these neurons process information about sounds only of a certain frequency, a certain pitch. The further alongauditory pathwayThe auditory center is located from the cochlea, the more complex sound signals excite its individual neurons. this suggests that an increasingly complex synthesis of individual characteristics of sound signals occurs in the auditory centers.
It cannot be assumed that information about sound signals is processed only sequentially during the transition of excitation from one auditory center to another. All auditory centers are interconnected by numerous complex connections, with the help of which not only the transfer of information in one direction is carried out, but also its comparative processing.
Diagram of auditory pathways
1 - cochlea (organ of Corti with hair cells - auditory receptors);
2 - spiral ganglion;
3 - anterior (ventral) cochlear (cochlear) nucleus;
4 - posterior (dorsal) cochlear (cochlear) nucleus;
5 - nucleus of the trapezoid body;
6 - upper olive;
7 - nucleus of the lateral loop;
8 - nuclei of the posterior colliculi of the midbrain quadrigeminal;
9 - medial geniculate body of the metathalamus of the diencephalon;
10 - projection auditory zone of the cerebral cortex.
Rice. 1. Diagram of auditory sensory pathways (according to Sentagotai).
1 - temporal lobe; 2 - midbrain; 3 - isthmus of the rhombencephalon; 4 - medulla oblongata; 5 - snail; 6 - ventral auditory nucleus; 7 - dorsal auditory nucleus; 8 - auditory stripes; 9 - olivo-auditory fibers; 10 - superior olive: 11 - nuclei of the trapezoid body; 12 - trapezoidal body; 13 - pyramid; 14 - lateral loop; 15 - nucleus of the lateral loop; 16 - triangle of the lateral loop; 17 - inferior colliculus; 18 - lateral geniculate body; 19 - cortical hearing center.
The structure of the auditory pathways
Schematic pathway of auditory excitation : auditory receptors (hair cells in the organ of Corti of the cochlea) - peripheral spiral ganglion (in the cochlea) - medulla oblongata (first the cochlear nuclei, i.e. cochlear, after them - the olivary nuclei) - midbrain (inferior colliculus) - diencephalon (medial geniculate bodies, also known as internal) - cerebral cortex (auditory zones of the temporal lobes, fields 41, 42).
First(I) auditory afferent neurons (bipolar neurons) are located in the spiral ganglion, or node (gangl. spirale), located at the base of the hollow cochlear spindle. The spiral ganglion consists of the bodies of auditory bipolar neurons. The dendrites of these neurons pass through the canals of the bony spiral plate to the cochlea, i.e. they begin from the outer hair cells of the organ of Corti. Axons leave the spiral ganglion and gather in the auditory nerve, which enters the brain stem in the region of the cerebellopontine angle, where they end with synapses on the nerve cells of the cochlear (cochlear) nuclei: dorsal (nucl. cochlearis dorsalis) and ventral (nucl. cochlearis ventralis). These cells of the cochlear nuclei are second auditory neurons (II).
The auditory nerve has the following names: N. vestibulocochlearis, sive n. octavus (PNA), n. acusticus (BNA), sive n. stato-acusticus - equilibrium-auditory (JNA). This is the VIII pair of cranial nerves, consisting of two parts: cochlear (pars cochlearis) and vestibular, or vestibular (pars vestibularis). The cochlear part is a set of axons of the first neurons of the auditory sensory system (bipolar neurons of the spiral ganglion), the vestibular part is the axons of afferent neurons of the labyrinth, providing regulation of the position of the body in space (in the anatomical literature, both parts are also called nerve roots).
Second auditory afferent neurons (II) are located in the dorsal and ventral cochlear (cochlear) nucleus of the medulla oblongata.
Two ascending auditory tracts begin from neurons of the second cochlear nuclei. The contralateral ascending auditory tract contains the bulk of the fibers emerging from the cochlear nuclei complex and forms three bundles of fibers: 1- ventral auditory strip, or trapezoid body, 2 - intermediate auditory strip, or strip of Held, 3 - back, or dorsal, auditory strip - Monakov's strip. The main part of the fibers contains the first bundle - the trapezoidal body. The middle, intermedial, stripe is formed by the axons of part of the cells of the posterior section of the posterior ventral nucleus of the cochlear complex. The dorsal auditory stria contains fibers coming from the cells of the dorsal cochlear nucleus, as well as axons of part of the cells of the posterior ventral nucleus. The fibers of the dorsal strip go along the bottom of the fourth ventricle, then go into the brain stem, cross the midline and, bypassing the olive without ending in it, join the lateral lemniscus of the opposite side, where they rise to the nuclei of the lateral lemniscus. This strip bypasses the superior cerebellar peduncle, then passes to the opposite side and joins the trapezius body.
So, axons of II neurons extending from cells dorsal nucleus (auditory tubercle), form brain striae (striae medullares ventriculi quarti), located in the rhomboid fossa on the border of the pons and medulla oblongata. Most of the medullary stria passes to the opposite side and, near the midline, is immersed in the substance of the brain, connecting to the lateral loop (lemniscus lateralis); the smaller part of the medullary stria is attached to the lateral loop of its own side. Numerous fibers emerging from the dorsal nucleus go as part of the lateral loop and end in the lower tubercles of the quadrigeminal colliculus inferior and in the internal (medial) geniculate body (corpus geniculatum mediate) of the thalamus, this is the diencephalon. Some of the fibers, bypassing the internal geniculate body (auditory center), go to the external (lateral) geniculate body of the thalamus, which is visual subcortical center of the diencephalon, which indicates a close connection between the auditory sensory system and the visual one.
Axons of II neurons from cells ventral nucleus participate in the formation of the trapezoidal body (corpus trapezoideum). Most of the axons in the lateral loop (lemniscus lateralis) pass to the opposite side and end in the superior olive of the medulla oblongata and the nuclei of the trapezoid body, as well as in the reticular nuclei of the tegmentum on auditory neurons III. Another, smaller part of the fibers ends on the same side in the same structures. Therefore, it is here, in the olives, that the comparison of acoustic signals coming from two sides from two different ears takes place. Olives provide binaural analysis of sounds, i.e. compare sounds from different ears. It is the olives that provide stereo sound and help accurately target the sound source.
Still others auditory afferent neurons (III) are located in the nuclei of the superior olive (1) and trapezoid body (2), as well as in the inferior colliculus of the midbrain (3) and in the internal (medial) geniculate bodies (4) of the diencephalon. Axons of III neurons participate in the formation of the lateral loop, which contains fibers of II and III neurons. Some fibers of II neurons are interrupted in the nucleus of the lateral lemniscus (nucl. lemnisci proprius lateralis). Thus, in the nucleus of the lateral lemniscus there are also III neurons. Fibers of II neurons of the lateral lemniscus switch to III neurons in the medial geniculate body (corpus geniculatum mediale). The fibers of III neurons of the lateral lemniscus, passing by the medial geniculate body, end in the inferior colliculus (colliculus inferior), where tr is formed. tectospinalis. Thus, in the inferior colliculus of the midbrain there is inferior auditory center, consisting of IV neurons.
Nerve fibers of the lateral lemniscus, which belong to the neurons of the superior olive, penetrate from the pons into the superior cerebellar peduncles and then reach its nuclei. Thus, the cerebellar nuclei receive auditory sensory stimulation from the auditory lower nerve centers of the olive. Another part of the axons of the superior olive goes to the motor neurons of the spinal cord and further to the striated muscles. Thus, the auditory lower nerve centers of the superior olive control effectors and provide motor auditory reflex reactions.
Axons of III neurons located in medial geniculate body(corpus geniculatum mediate), passing through the back of the posterior leg of the internal capsule, form auditory glow, which ends on IV neurons in - Heschl’s transverse gyrus of the temporal lobe (fields 41, 42, 20, 21, 22). So, the axons of III neurons of the medial geniculate bodies form the central auditory pathway leading to the auditory sensory primary projection zones of the cerebral cortex. In addition to the ascending afferent fibers, descending efferent fibers also pass through the central auditory pathway - from the cortex to the lower subcortical auditory centers.
Fourth auditory afferent neurons (IV) are located both in the inferior colliculus of the midbrain and in the temporal lobe of the cerebral cortex (Brodmann's areas 41, 42, 20, 21, 22).
The inferior colliculus is reflex motor center, through which tr is connected. tectospinalis. Thanks to this, during auditory irritation, the spinal cord is reflexively connected to perform automatic movements, which is facilitated by the connection of the superior olive with the cerebellum; The medial longitudinal fascicle (fasc. longitudinalis medialis) is also connected, combining the functions of the motor nuclei of the cranial nerves. Destruction of the inferior colliculus is not accompanied by hearing loss, but it plays an important role as a “reflex” subcortical center, in which the efferent part of the indicative auditory reflexes in the form of eye and head movements is formed.
The bodies of cortical neurons IV form columns of the auditory cortex, which form the primary auditory images. From some IV neurons there are pathways through the corpus callosum to the opposite side, into the auditory cortex of the contralateral (opposite) hemisphere. This is the final pathway for auditory sensory stimulation. It also ends on IV neurons. Auditory sensory images are formed in higher auditory nerve center of the cortex- Heschl’s transverse gyrus of the temporal lobe (fields 41, 42, 20, 21, 22). Low sounds are perceived in the anterior parts of the superior temporal gyrus, and high sounds are perceived in its posterior parts. Fields 41 and 42, as well as 41/42 of the temporal region of the cortex belong to the small-cell (pulverized, koniocortical) sensory fields of the cerebral cortex. They are located on the upper surface of the temporal lobe, hidden in the depths of the lateral (Sylvian) fissure. In area 41, the smallest and most densely cellular, most of the afferent fibers of the auditory sensory system end. Other fields of the temporal region (22, 21, 20 and 37) perform higher auditory functions, for example, they participate in auditory gnosis. Auditory gnosis (gnosis acustica) is the recognition of an object by its characteristic sound.
Disorders (pathology)
When there is a disease in the peripheral parts of the auditory sensory system, noise and sounds of a different nature appear in auditory perception.
Decreased hearing of central origin is characterized by a violation of the higher acoustic (sound) analysis of sound stimuli. Sometimes there is a pathological exacerbation or distortion of hearing (hyperacusis, paracusia).
With cortical damage, sensory aphasia and auditory agnosia occur. Hearing disorder is observed in many organic diseases of the central nervous system.
The doctrine of the cytoarchitectonics of the cerebral cortex corresponds to the teaching of I.P. Pavlova about the cortex as a system of cortical ends of analyzers. The analyzer, according to Pavlov, “is a complex nervous mechanism that begins with the external perceptive apparatus and ends in the brain.” The analyzer consists of three parts - the external perceptive apparatus (sensory organ), the conductive part (conducting tracts of the brain and spinal cord) and the final cortical end (center ) in the cerebral cortex of the telencephalon. According to Pavlov, the cortical end of the analyzer consists of a “core” and “scattered elements.”
Analyzer core According to structural and functional features, they are divided into the central field of the nuclear zone and the peripheral one. In the first, finely differentiated sensations are formed, and in the second, more complex forms of reflection of the external world.
Trace elements represent those neurons that are located outside the nucleus and carry out simpler functions.
Based on morphological and experimental-physiological data in the cerebral cortex, the most important cortical ends of the analyzers (centers), which through interaction provide brain functions, have been identified.
The localization of the core analyzers is as follows:
Cortical end of the motor analyzer(precentral gyrus, precentral lobule, posterior part of the middle and inferior frontal gyri). The precentral gyrus and the anterior section of the pericentral lobule are part of the precentral region - the motor or motor zone of the cortex (cytoarchitectonic fields 4, 6). In the upper part of the precentral gyrus and the precentral lobule there are motor nuclei of the lower half of the body, and in the lower part - the upper half. The largest area of the entire zone is occupied by the centers of innervation of the hand, face, lips, tongue, and the smaller area is occupied by the centers of innervation of the muscles of the trunk and lower extremities. This area was previously considered to be only motor, but is now considered to be the region containing interneurons and motor neurons. Interneurons perceive stimuli from proprioceptors of bones, joints, muscles and tendons. The centers of the motor zone innervate the opposite part of the body. Dysfunction of the precentral gyrus leads to paralysis on the opposite side of the body.
Core of the motor analyzer for combined head and eye rotation in the opposite direction, as well as Motor nuclei of written speech - graphs related to voluntary movements associated with writing letters, numbers and other characters are localized in the posterior part of the middle frontal gyrus (field 8) and on the border of the parietal and occipital lobes (field 19) . The center of the graph is also closely connected with area 40, located in the supramarginal gyrus. If this area is damaged, the patient cannot make the movements necessary to draw letters.
Premotor zone located anterior to the motor areas of the cortex (fields 6 and 8). The processes of the cells of this zone are connected both with the nuclei of the anterior horns of the spinal cord, and with the subcortical nuclei, red nucleus, substantia nigra, etc.
Core of the motor speech articulation analyzer(speech-motor analyzer) are located in the posterior part of the inferior frontal gyrus (field 44, 45, 45a). In field 44 - Broca's area, in right-handed people - in the left hemisphere, the analysis of irritations from the motor apparatus is carried out, through which syllables, words, and phrases are formed. This center was formed next to the projection area of the motor analyzer for the muscles of the lips, tongue, and larynx. When it is affected, a person is able to pronounce individual speech sounds, but he loses the ability to form words from these sounds (motor or motor aphasia). In case of damage to field 45, the following is observed: agrammatism - the patient loses the ability to compose words from words, to coordinate words into sentences.
Cortical end of the motor analyzer of complex coordinated movements in right-handers it is located in the inferior parietal lobule (area 40) in the region of the supramarginal gyrus. When field 40 is affected, the patient, despite the absence of paralysis, loses the ability to use household items and loses production skills, which is called apraxia.
Cortical end of a skin analyzer of general sensitivity- temperature, pain, tactile, muscle-articular - located in the postcentral gyrus (fields 1, 2, 3, 5). Damage to this analyzer results in loss of sensitivity. The sequence of locations of the centers and their territory corresponds to the motor zone of the cortex.
Cortical end of the auditory analyzer(field 41) is located in the middle part of the superior temporal gyrus.
Hearing speech analyzer(control of one’s own speech and perception of someone else’s) is located in the posterior part of the superior temporal gyrus (field 42) (Wernicke’s area_ when it is disrupted, a person hears speech, but does not understand it (sensory aphasia)
Cortical end of the visual analyzer(fields 17, 18, 19) occupies the edges of the calcarine groove (field 17), complete blindness occurs with bilateral damage to the nuclei of the visual analyzer. In cases of damage to fields 17 and 18, loss of visual memory is observed. If field 19 is damaged, a person loses the ability to navigate in a new environment.
Visual analyzer of written characters located in the angular gyrus of the inferior parietal lobule (area 39s). If this field is damaged, the patient loses the ability to analyze written letters, that is, loses the ability to read (Alexia)
Cortical ends of the olfactory analyzer are located in the uncinate parahippocampal gyrus on the inferior surface of the temporal lobe and the hippocampus.
Cortical ends of the taste analyzer- in the lower part of the postcentral gyrus.
Cortical end of the stereognostic sense analyzer- the center of a particularly complex type of recognition of objects by touch is located in the superior parietal lobule(field 7). If the parietal lobule is damaged, the patient cannot recognize an object by feeling it with the hand opposite to the lesion - Stereognosia. Distinguish auditory gnosis- recognition of objects by sound (a bird by its voice, a car by the noise of its engines), visual gnosis- recognition of objects by appearance, etc. Praxia and gnosis are functions of a higher order, the implementation of which is associated with both the first and second signaling systems, which is a specific human function.
Any function is not localized in one specific field, but is only predominantly associated with it and spreads over a large area.
Speech- is one of the phylogenetically new and most complexly localized functions of the cortex associated with the second signaling system, according to I.P. Pavlova. Speech appeared in the course of human social development, as a result of labor activity. “... First, work, and then, along with it, articulate speech were the two most important stimuli, under the influence of which the monkey’s brain gradually turned into the human brain, which, for all its similarities with monkeys, far surpasses it in size and perfection” ( K. Marx, F. Engels)
The function of speech is extremely complex. It cannot be localized in any part of the cortex; the entire cortex, namely neurons with short processes located in its superficial layers, participates in its implementation. With the development of new experience, speech functions can move to other areas of the cortex, such as gesturing in the deaf and dumb, reading in the blind, writing with the foot in the armless. It is known that in the majority of right-handed people, speech functions, functions of recognition (gnosis), and purposeful action (praxia) are associated with certain cytoarchitectonic fields of the left hemisphere, while in left-handers it is the other way around.
Association cortical areas occupy the remaining significant part of the cortex, they lack obvious specialization and are responsible for combining and processing information and programmed action. The associative cortex forms the basis of higher processes, such as memory, learning, thinking, and speech.
There are no zones that give rise to thoughts. To make the most insignificant decision, the entire brain is involved, various processes occurring in different zones of the cortex and in the lower nerve centers come into play.
The cerebral cortex receives information, processes it and stores it in memory. In the process of adaptation (adaptation) of the body to the external environment, complex systems of self-regulation and stabilization were formed in the cortex, providing a certain level of function, self-learning systems with a memory code, control systems operating on the basis of a genetic code, taking into account age and ensuring an optimal level of control and functions in the body , comparison systems that provide a transition from one form of management to another.
Connections between the cortical ends of a particular analyzer with the peripheral parts (receptors) are carried out by a system of pathways of the brain and spinal cord and peripheral nerves extending from them (cranial and spinal nerves).
Subcortical nuclei. They are located in the white matter of the base of the telencephalon and form three paired clusters of gray matter: striatum, amygdala and fence, which constitute approximately 3% of the volume of the hemispheres.
Striatum o consists of two nuclei: caudate and lentiform.
Caudate nucleus is located in the frontal lobe and is a formation in the form of an arc lying on top of the visual thalamus and the lenticular nucleus. It consists of head, body and tail, which take part in the formation of the lateral part of the wall of the anterior horn of the lateral ventricle of the brain.
Lenticular nucleus a large pyramidal-shaped accumulation of gray matter located lateral to the caudate nucleus. The lentiform nucleus is divided into three parts: the outer, dark-colored - shell and two light medial stripes - the outer and inner segments pale globe.
From each other caudate and lenticular nuclei separated by a layer of white matter - part internal capsule. Another part of the internal capsule separates the lenticular nucleus from the underlying thalamus.
The striatum forms striopallidal system, in which the more ancient structure in phylogenetic terms is the globus pallidus - pallidum. It is separated into an independent morpho-functional unit that performs a motor function. Thanks to connections with the red nucleus and the black substance of the midbrain, the pallidum carries out movements of the torso and arms when walking - cross-coordination, a number of auxiliary movements when changing body positions, facial movements. Destruction of the globus pallidus causes muscle rigidity.
The caudate nucleus and putamen are younger structures of the striatum - striatum, which does not directly have a motor function, but performs a controlling function in relation to the pallidum, somewhat inhibiting its influence.
When the caudate nucleus is damaged, a person experiences rhythmic involuntary movements of the limbs (Huntington's chorea), and when the putamen is degenerated, trembling of the limbs occurs (Parkinson's disease).
Fence- a relatively thin strip of gray matter located between the insular cortex, separated from it by white matter - outer capsule and the shell from which it is separated outer capsule. The fence is a complex formation, the connections of which have so far been poorly studied, and the functional significance is not clear.
Amygdala- a large nucleus, located under the shell in the depths of the anterior temporal lobe, has a complex structure and consists of several nuclei that differ in cellular composition. The amygdala is a subcortical olfactory center and is part of the limbic system.
The subcortical nuclei of the telencephalon function in close relationship with the cerebral cortex, diencephalon and other parts of the brain, and take part in the formation of both conditioned and unconditioned reflexes.
Together with the red nucleus, the substantia nigra of the midbrain, the thalamus of the diencephalon, the subcortical nuclei form extrapyramidal system, carrying out complex unconditioned reflex motor acts.
Olfactory brain in humans is the most ancient part of the telencephalon, which arose in connection with olfactory receptors. It is divided into two sections: peripheral and central.
To the peripheral section include: olfactory bulb, olfactory tract, olfactory triangle and anterior perforated substance.
Part central department and includes: vaulted gyrus, consisting of cingulate cortex, isthmus and parahippocampal gyrus, and hippocampus- a peculiarly shaped formation located in the cavity of the lower horn of the lateral ventricle and dentate gyrus, lying inside the hippocampus.
Limbic system(edge, edge) is so named because the cortical structures included in it are located on the edge of the neocortex and, as it were, border the brain stem. The limbic system includes both certain zones of the cortex (archipaleocortical and interstitial areas) and subcortical formations.
Of the cortical structures these are: hippocampus with dentate gyrus(old bark), cingulate gyrus(limbic cortex, which is interstitial), olfactory cortex, septum(ancient bark).
From subcortical structures: mamillary body of the hypothalamus, anterior nucleus of the thalamus, amygdala complex, and vault
In addition to numerous two-way connections between the structures of the limbic system, there are long paths in the form of closed circles along which excitation circulates. Great limbic circle - Peipets circle includes: hippocampus, fornix, mammillary body, mastoid-thalamic fascicle(Vic d'Azira bundle), anterior nucleus of the thalamus, cingulate cortex, hippocampus. Of the overlying structures, the limbic system has the closest connections with the frontal cortex. The limbic system directs its descending pathways to the reticular formation of the brain stem and to the hypothalamus.
Through the hypothalamic-pituitary system, it exercises control over the humoral system. The limbic system is characterized by special sensitivity and a special role in the functioning of hormones synthesized in the hypothalamus, oxytocin and vasopressin, secreted by the pituitary gland.
The main integral function of the limbic system is not only the olfactory function, but also the reactions of the so-called innate behavior (eating, sexual, searching and defensive). It carries out the synthesis of afferent stimuli, is important in the processes of emotional and motivational behavior, organizes and ensures the flow of vegetative, somatic and mental processes during emotional and motivational activity, carries out the perception and storage of emotionally significant information, the selection and implementation of adaptive forms of emotional behavior.
Thus, the functions of the hippocampus are associated with memory, learning, the formation of new behavior programs when conditions change, and the formation of emotional states. The hippocampus has extensive connections with the cerebral cortex and the hypothalamus of the diencephalon. In mentally ill patients, all layers of the hippocampus are affected.
At the same time, each structure included in the limbic system contributes to a single mechanism, having its own functional characteristics.
Anterior limbic cortex provides emotional expressiveness of speech.
Cingulate gyrus takes part in reactions of alertness, awakening, and emotional activity. It is connected by fibers to the reticular formation and the autonomic nervous system.
Amygdala complex responsible for feeding and defensive behavior; stimulation of the amygdala causes aggressive behavior.
Partition takes part in retraining, reduces aggressiveness and fear.
Mamillary bodies play a big role in developing spatial skills.
Anterior to the arch in its various sections there are centers of pleasure and pain.
Lateral ventricles are the cavities of the hemispheres of the telencephalon. Each ventricle has a central part adjacent to the superior surface of the optic thalamus in the parietal lobe and three horns extending from it.
Front horn goes to the frontal lobe posterior horn- into the occipital lobe, the lower horn - into the depth of the temporal lobe. In the lower horn there is an elevation of the inner and partially lower wall - the hippocampus. The medial wall of each anterior horn is a thin transparent plate. The right and left plates form a common transparent septum between the anterior horns.
The lateral ventricles, like all ventricles of the brain, are filled with cerebral fluid. Through the interventricular foramina, which are located in front of the visual thalamus, the lateral ventricles communicate with the third ventricle of the diencephalon. Most of the walls of the lateral ventricles are formed by the white matter of the telencephalon hemispheres.
White matter of the telencephalon. It is formed by fibers of conductive tracts, which are grouped into three systems: associative or combinational, commissural or commissural and projection.
Association fibers The telencephalon connects different parts of the cortex within one hemisphere. They are divided into short fibers, lying superficially and arcuately, connecting the cortex of two adjacent gyri, and long fibers, lying deeper and connecting areas of the cortex distant from each other. These include:
1) Belt, which can be traced from the anterior perforated substance to the hippocampal gyrus and connects the gyral cortex of the medial part of the surface of the hemisphere - refers to the olfactory brain.
2) Lower longitudinal beam connects the occipital lobe with the temporal lobe, runs along the outer wall of the posterior and inferior horn of the lateral ventricle.
3) Upper longitudinal beam connects the frontal, parietal and temporal lobes.
4) Hooked bundle connects the rectus and orbital gyri of the frontal lobe with the temporal lobe.
Commissural nerve pathways connect the cortical areas of both hemispheres. They form the following commissures or commissures:
1) Corpus callosum the largest commissure that connects various areas of the neocortex of both hemispheres. In humans it is much greater than in animals. In the corpus callosum, there is an anterior end curved downwards (beaked) - the knee of the corpus callosum, a middle part - the trunk of the corpus callosum and a thickened posterior end - the splenium of the corpus callosum. The entire surface of the corpus callosum is covered with a thin layer of gray matter - the gray vesture.
In women, more fibers pass through a certain area of the corpus callosum than in men. Thus, interhemispheric connections in women are more numerous, and therefore they are better able to integrate information available in both hemispheres, which explains gender differences in behavior.
2) Anterior callosal commissure located behind the beak of the corpus callosum and consists of two bundles; one connects the anterior perforated substance, and the other connects the gyri of the temporal lobe, mainly the hippocampal gyrus.
3) Vault commissure connects the central parts of two arcuate bundles of nerve fibers, which form a vault located under the corpus callosum. The vault is divided into a central part - the pillars of the vault and the legs of the vault. The columns of the fornix connect a triangular plate - the commissure of the fornix, the posterior part of which is fused with the lower surface of the corpus callosum. The columns of the fornix, curving posteriorly, enter the hypothalamus and end in the mamillary bodies.
Projection pathways connect the cerebral cortex with the nuclei of the brain stem and spinal cord. There are: efferent- descending motor pathways that conduct nerve impulses from the cells of the motor areas of the cortex to the subcortical nuclei, motor nuclei of the brain stem and spinal cord. Thanks to these pathways, the motor centers of the cerebral cortex are projected to the periphery. Afferent- ascending sensory pathways are processes of cells of the spinal ganglia and ganglia of the cranial nerves - these are the first neurons of the sensory pathways that end on the switching nuclei of the spinal cord or medulla oblongata, where the second neurons of the sensory pathways are located, going as part of the medial loop to the ventral nuclei of the thalamus. In these nuclei lie the third neurons of the sensory pathways, the processes of which go to the corresponding nuclear centers of the cortex.
Both sensory and motor pathways form in the substance of the cerebral hemispheres a system of radiating fascicles - the corona radiata, which gathers into a compact and powerful bundle - the internal capsule, which is located between the caudate and lenticular nuclei, on the one hand, and the thalamus, on the other hand. It distinguishes between the front leg, the knee and the back leg.
The pathways of the brain are the spinal cords.
The membranes of the brain. The brain, like the spinal cord, is covered with three membranes - dura mater, arachnoid membrane and vascular membrane.
Dura shell and the brain differs from that of the spinal cord in that it is fused to the inner surface of the skull bones, and there is no epidural space. The dura mater forms channels for the outflow of venous blood from the brain - the sinuses of the dura mater and gives rise to processes that provide fixation of the brain - these are the falx cerebri (between the right and left hemispheres of the brain), the tentorium cerebellum (between the occipital lobes and the cerebellum) and the diaphragm sella (above sella turcica, in which the pituitary gland is located). In the places where the processes depart, the dura mater is stratified, forming sinuses, where venous blood of the brain, dura mater, and skull bones flows into the system of external veins through the graduates.
Arachnoid The brain is located under the dura and covers the brain without entering its grooves, spreading over them in the form of bridges. On its surface there are outgrowths - Pachionian granulations, which have complex functions. Between the arachnoid and choroid, a subarachnoid space is formed, well defined in the cisterns that form between the cerebellum and medulla oblongata, between the cerebral peduncles, in the region of the lateral sulcus. The subarachnoid space of the brain communicates with those of the spinal cord and the fourth ventricle and is filled with circulating cerebral fluid.
Choroid The brain consists of 2 plates, between which arteries and veins are located. It is closely fused with the substance of the brain, enters all the cracks and grooves and participates in the formation of choroid plexuses, rich in blood vessels. Penetrating into the ventricles of the brain, the choroid produces cerebral fluid, thanks to its choroid plexuses.
Lymphatic vessels not found in the membranes of the brain.
The innervation of the meninges is carried out by the V, X, XII pairs of cranial nerves and the sympathetic nerve plexus of the internal carotid and vertebral arteries.
