I pair – olfactory nerves, nervi olfactorii. Olfactory tract

Anatomy

The olfactory nerves are nerves of special sensitivity - olfactory. They begin from the olfactory neurosensory cells, forming first neuron of the olfactory pathway and located in the olfactory region of the nasal mucosa. In the form of 15-20 thin nerve trunks (olfactory filaments), consisting of unmyelinated nerve fibers, they, without forming a common trunk of the olfactory nerve, penetrate through the horizontal plate of the ethmoid bone (lat. lamina cribrosa ossis ethmoidalis) into the cranial cavity, where they enter the olfactory bulb (lat. bulbus olfactorius) (here lies body of the second neuron), passing into the olfactory tract (lat. tractus olfactorius), which are axons of cells located in the olfactory bulbs (lat. bulbus olfactorius). The olfactory tract passes into the olfactory triangle (lat. trigonum olfactorium). The latter consists mainly of nerve cells and is divided into two olfactory stripes, entering the anterior perforated substance (lat. area subcallosa and transparent septum (lat. septum pellucidum), where there are cell bodies of third neurons. Then the fibers of the cells of these formations in various ways reach the cortical end of the olfactory analyzer, which lies in the area of ​​the hook (lat. uncus) and the parahippocampal gyrus lat. gyrus parahyppocampalis of the temporal lobe of the cerebral hemispheres.

Function

Olfactory nerves are nerves of special sensitivity.

The olfactory system begins with the olfactory part of the nasal mucosa (the area of ​​the upper nasal passage and the upper part of the nasal septum). It contains the bodies of the first neurons of the olfactory analyzer. These cells are bipolar.

As noted above, the olfactory analyzer is a three-neuron circuit:

1. The bodies of the first neurons are represented by bipolar cells located in the nasal mucosa. Their dendrites end on the surface of the nasal mucosa and form the olfactory receptor apparatus. The axons of these cells in the form of olfactory filaments end on the bodies of second neurons, morphologically located in the olfactory bulbs
2. The axons of the second neurons form the olfactory tracts, which end on the bodies of the third neurons in the anterior perforated substance (lat. substantia perforata anterior), lat. area subcallosa and transparent septum (lat. septum pellucidum)
3. Cell bodies of third neurons are also called primary olfactory centers. It is important to note that the primary olfactory centers are connected to the cortical territories of both their own and the opposite side; The transition of part of the fibers to the other side occurs through the anterior commissure (lat. comissura anterior). In addition, it provides a connection with the limbic system. The axons of the third neurons are directed to the anterior parts of the parahippocampal gyrus, where Brodmann's cytoarchitectonic area is located 28. This area of ​​the cortex contains the projection fields and the association zone of the olfactory system.

An appetizing odor simultaneously triggers the salivation reflex, while an unpleasant odor leads to nausea and vomiting. These reactions are associated with emotions. Smells can be pleasant or unpleasant. The main fibers that provide connection between the olfactory system and the autonomous areas of the brain are the fibers of the medial bundles of the forebrain and the medullary striae of the visual thalamus.

The medial forebrain bundle consists of fibers that ascend from the basal olfactory area, the peramygdala, and the septal nuclei. On their way through the hypothalamus, some of the fibers end on the nuclei of the subthalamic region. Most of the fibers are directed to the brain stem and make contact with the vegetative zones of the reticular formation, with the salivary and dorsal lat nuclei. n.intermedius ( Wriesberg nerve), glossopharyngeal (lat. n. glossopharyngeus) and vagus (lat. n.vagus) nerves.

The medullary striae of the optic thalamus give off synapses to the leash nuclei. From these nuclei it goes to the interpeduncular nucleus (Ganser's node) and to the tegmental nuclei. leash-pedicle path, and from them the fibers are directed to the vegetative centers of the reticular formation of the brain stem.

The fibers that connect the olfactory system with the thalamus opticus, the hypothalamus and the limbic system probably provide the accompaniment of olfactory stimuli with emotions. The septal area, in addition to other brain areas, is connected through associative fibers with the cingulate gyrus (lat. gyrus cinguli).

Clinic of the lesion

Anosmia and hyposmia

Anosmia (lack of sense of smell) or hyposmia (decreased sense of smell) on both sides is more often observed in diseases of the nasal mucosa. Hyposmia or anosmia on one side is usually a sign of a serious illness.

Possible causes of anosmia:

1. Underdevelopment of the olfactory pathways.
2. Diseases of the olfactory mucosa of the nose (rhinitis, nasal tumors, etc.).
3. Rupture of the olfactory filaments during a fracture of the lamina cribrosa of the ethmoid bone due to traumatic brain injury.
4. Destruction of the olfactory bulbs and tracts at the source of the bruise according to the type of counter-impact, observed when falling on the back of the head
5. Inflammation of the ethmoid bone sinuses (lat. os ethmoidae, inflammatory process of the adjacent pia mater and surrounding areas.
6. Median tumors or other space-occupying formations of the anterior cranial fossa.

It should be noted that interruption of the integrity of the pathways coming from the primary olfactory centers does not lead to anosmia, since they are bilateral.

Hyperosmia

Hyperosmia - an increased sense of smell is observed in some forms of hysteria and sometimes in cocaine addicts.

Parosmia

A perverted sense of smell is observed in some cases

Also

The olfactory nerve can serve as a portal of entry for brain and meningeal infections. The patient may not be aware of the loss of smell. Instead, due to the disappearance of the sense of smell, he may complain of a violation of the sense of taste, since the perception of smells is very important for the formation of the taste of food (there is a connection between the olfactory system and the Latin nucleus tractus solitarii).

Research methodology

The state of smell is characterized by the ability to perceive odors of varying intensity by each half of the nose separately and identify (recognize) different odors. With calm breathing and closed eyes, a finger is pressed against the wing of the nose on one side and the odorous substance is gradually brought closer to the other nostril. It is better to use familiar non-irritating odors (volatile oils): laundry soap, rose water (or cologne), bitter almond water (or valerian drops), camphor. The use of irritating substances such as ammonia or vinegar should be avoided, since this simultaneously causes irritation of the endings of the trigeminal nerve (lat. n.trigeminus). It is noted whether odors are correctly identified. In this case, it is necessary to keep in mind whether the nasal passages are free or whether there are catarrhal phenomena from them. Although the subject may be unable to name the substance being tested, the mere awareness of the presence of the odor rules out anosmia.

Literature

1. Bing Robert Compendium of topical diagnostics of the brain and spinal cord. A brief guide to the clinical localization of diseases and lesions of the nerve centers Translation from the second edition - Printing house of P. P. Soykin - 1912
2. Gusev E.I., Konovalov A.N., Burd G.S. Neurology and neurosurgery: Textbook. - M.: Medicine, 2000
3. Duus P. Topical diagnosis in neurology Anatomy. Physiology. Clinic - M. IPC "Vazar-Ferro", 1995
4. Nervous illnesses / S. M. Vinichuk, E. G. Dubenko, E. L. Macheret et al.; Per ed. S. M. Vinichuk, E. G. Dubenka - K.: Health, 2001
5. Pulatov A. M., Nikiforov A. S. Propaedeutics of nervous diseases: A textbook for students of medical institutes - 2nd ed. - T.: Medicine, 1979
6. Sinelnikov R. D., Sinelnikov Ya. R. Atlas of human anatomy: Textbook. Benefit. - 2nd ed., stereotypical - In 4 volumes. T.4. - M.: Medicine, 1996
7. Triumphov A.V. topical diagnosis of diseases of the nervous system M.: MEDpress LLC. 1998

The pathways of the olfactory analyzer (tractus olfactorius) have a complex structure. The olfactory receptors of the nasal mucosa perceive changes in the chemistry of the air and are the most sensitive compared to the receptors of other senses. First neuron formed by bipolar cells located in the mucous membrane of the superior turbinate and nasal septum. The dendrites of the olfactory cells have club-shaped thickenings with numerous cilia that perceive air chemicals; axons connect to olfactory filaments(fila olfactoria), penetrating through the openings of the cribriform plate into the cranial cavity, and are switched in the olfactory glomeruli olfactory bulb(bulbus olfactorius) to the second neuron . Axons of the second neuron(neutral cells) form olfactory tract and end at olfactory triangle(trigonum olfactorium) and in anterior perforated substance(substantia perforata anterior), where the cells of the third neuron are located. Axons of the third neuron grouped into three bundles - external, intermediate, medial, which are directed to various brain structures. External beam, going around the lateral sulcus of the cerebrum, reaches the cortical center of smell, located in hook(uncus) of the temporal lobe. Intermediate beam, passing in the hypothalamic region, ends in mastoid bodies and in the midbrain ( red core). Medial bundle is divided into two parts: one part of the fibers, passing through the gyrus paraterminalis, goes around the corpus callosum, enters the vaulted gyrus, reaches the hippocampus And hook; the other part of the medial fascicle forms olfactory-leash bundle nerve fibers passing through brain stripes(stria medullaris) of the thalamus on its own side. The olfactory-lead fascicle ends in the nuclei of the triangle of the frenulum of the suprathalamic region, where the descending pathway begins, connecting the motor neurons of the spinal cord. Nuclei of the triangular frenulum duplicated by a second system of fibers coming from the mastoid bodies.

The olfactory system has not undergone dramatic changes during evolution and has no representation in the neocortex.

Auditory sensory system

Auditory system , auditory analyzer - a set of mechanical, receptor and neural structures that perceive and analyze sound vibrations. The structure of the auditory system, especially its peripheral part, may vary in different animals. Thus, a typical sound receiver in insects is the tympanic organ; one of the sound receivers in bony fish is the swim bladder, the vibrations of which, under the influence of sound, are transmitted to the Weberian apparatus and further to the inner ear. In amphibians, reptiles and birds, additional receptor cells (basilar papilla) develop in the inner ear. In higher vertebrates, including most mammals, the auditory system consists of the outer, middle and inner ears, the auditory nerve and successively connected nerve centers (the main ones are the cochlear and superior olive nuclei, the posterior tubercles of the quadrigeminal, the auditory cortex).

The development of the central part of the auditory system depends on environmental factors and on the importance of the auditory system in animal behavior. The auditory nerve fibers travel from the cochlea to the cochlear nuclei. Fibers from the right and left cochlear nuclei go to both symmetrical sides of the auditory system. Afferent fibers from both ears converge in the superior olive. In the frequency analysis of sound, a significant role is played by the cochlear septum - a kind of mechanical spectral analyzer that functions as a series of mutually mismatched filters, spatially scattered along the cochlear septum, the vibration amplitude of which ranges from 0.1 to 10 nm (depending on the sound intensity).

The central parts of the auditory system are characterized by a spatially ordered position of neurons with maximum sensitivity to a certain sound frequency. The nervous elements of the auditory system, in addition to frequency, exhibit a certain selectivity to the intensity, duration of sound, etc. Neurons of the central, especially higher parts of the auditory system, selectively respond to complex signs of sounds (for example, to a certain frequency of amplitude modulation, to the direction of frequency modulation and sound movement ).

The auditory analyzer includes the hearing organ, the pathways of auditory information and the central representation in the cerebral cortex.

Hearing organ

Organa audites - labyrinth, which contains two types of receptors: one of them (organ of Corti) serve to perceive sound stimuli, others represent perceiving devices static-kinetic apparatus, necessary for the perception of the forces of gravity, to maintain balance and orientation of the body in space. At low stages of development, these two functions are not differentiated from each other, but the static function is primary. The prototype of a labyrinth in this sense can be a static bubble (oto- or statocyst), which is very common among invertebrate animals living in water, such as mollusks. In vertebrates, this initially simple form of the vesicle becomes significantly more complex as the functions of the labyrinth become more complex.

Genetically, the vesicle originates from the ectoderm by invagination followed by lacing, then the tube-like appendages of the static apparatus - the semicircular canals - begin to separate. Hagfish have one semicircular canal connected to a single vesicle, as a result of which they can move only in one direction; cyclostomes have two semicircular canals, thanks to which they are able to move their body in two directions. Starting with fish, all other vertebrates develop 3 semicircular canals, corresponding to the three dimensions of space existing in nature, allowing them to move in all directions.

As a result, vestibule of the labyrinth and semicircular canals having a special nerve - n. vestibularis. With access to land, with the advent of locomotion using limbs in terrestrial animals, and upright walking in humans, the importance of balance increases. While the vestibular apparatus is formed in aquatic animals, the acoustic apparatus, which is in its infancy in fish, develops only with access to land, when direct perception of air vibrations becomes possible. It gradually separates from the rest of the labyrinth, spiraling into a cochlea.

With the transition from the aqueous to the air environment, a sound-conducting apparatus is attached to the inner ear. Starting with amphibians, it appears middle ear- tympanic cavity with eardrum and auditory ossicles. The acoustic apparatus reaches its highest development in mammals, which have a spiral cochlea with a very complex sound-sensitive device. They have a separate nerve (n. cochlearis) and a number of auditory centers - subcortical (in the hindbrain and midbrain) and cortical. They also have outer ear with a recessed ear canal and auricle.

Auricle represents a later acquisition that plays the role of a speaker to amplify sound, and also serves to protect the external auditory canal. In terrestrial mammals, the auricle is equipped with special muscles and easily moves in the direction of sound. It is absent in mammals leading an aquatic and underground lifestyle; in humans and higher primates it undergoes reduction and becomes immobile. At the same time, the emergence of oral speech in humans is associated with the maximum development of auditory centers, especially in the cerebral cortex, which form part of the second signaling system.

The embryogenesis of the organ of hearing and balance in humans proceeds similarly to phylogenesis. At the 3rd week of embryonic life, on both sides of the posterior medullary vesicle, an auditory vesicle appears from the ectoderm - the rudiment of the labyrinth. By the end of 4 weeks, a blind duct (ductus endolymphaticus) and 3 semicircular canals grow from it. The upper part of the auditory vesicle, into which the semicircular canals flow, represents the rudiment of the elliptical sac (utriculus), it is separated at the point where the endolymphatic duct departs from the lower part of the vesicle - the rudiment of the future spherical sac (sacculus). At the 5th week of embryonic life, from the anterior part of the auditory vesicle corresponding to the sacculus, a small protrusion (lagena) first occurs, growing into a spiral-twisted cochlea passage (ductus cochlearis). Initially, the walls of the vesicle cavity, due to the ingrowth of peripheral processes of nerve cells from the auditory ganglion lying on the anterior side of the labyrinth, turn into sensory cells (organ of Corti). The mesenchyme adjacent to the membranous labyrinth turns into connective tissue, creating perilymphatic spaces around the formed utriculus, sacculus and semicircular canals. In the 6th month of intrauterine life, around the membranous labyrinth with its perilymphatic spaces, a bone labyrinth arises from the perichondrium of the cartilaginous capsule of the skull through perichondral ossification, repeating in general the shape of the membranous labyrinth.

Middle ear- tympanic cavity with auditory tube - develops from the first pharyngeal pouch and the lateral part of the upper wall of the pharynx, therefore, the epithelium of the mucous membrane of the middle ear cavities comes from the endoderm. The auditory ossicles located in the tympanic cavity are formed from the cartilage of the first (malleus and incus) and second (stirrup) visceral arches. The outer ear develops from the first gill pouch.

In a newborn, the auricle is relatively smaller than in an adult and does not have pronounced convolutions and tubercles. Only by the age of 12 does it reach the shape and size of the auricle of an adult. After 50 - 60 years, the cartilage begins to dehydrate. The external auditory canal in a newborn is short and wide, and the bony part consists of a bony ring. The size of the eardrum in a newborn and an adult is almost the same. The eardrum is located at an angle of 180° to the upper wall, and in an adult - at an angle of 140°.

Tympanic cavity filled with fluid and connective tissue cells, its lumen is small due to the thick mucous membrane. In children under 2 - 3 years of age, the upper wall of the tympanic cavity is thin, has a wide stony-scaly gap filled with fibrous connective tissue with numerous blood vessels. The posterior wall of the tympanic cavity communicates through a wide opening with the cells of the mastoid process. The auditory ossicles, although they contain cartilaginous points, correspond to the size of an adult. The auditory tube is short and wide (up to 2 mm). The shape and size of the inner ear do not change throughout life.

Sound waves, meeting the resistance of the eardrum, together with it vibrate the handle of the hammer, which displaces all the auditory ossicles. The base of the stapes presses on the perilymph of the vestibule of the inner ear. Since the fluid is practically incompressible, the perilymph of the vestibule displaces the fluid column of the scala vestibule, which moves through the opening at the apex of the cochlea (helicotrema) into the scala tympani. Its liquid stretches the secondary membrane covering the round window. Due to the deflection of the secondary membrane, the cavity of the perilymphatic space increases, which causes the formation of waves in the perilymph, the vibrations of which are transmitted to the endolymph. This leads to displacement of the spiral membrane, which stretches or bends the hairs of sensory cells. Sensory cells are in contact with the first sensory neuron.

Outer ear

The outer ear (auris externa) is a structural formation of the hearing organ, which includes Auricle, external auditory canal and eardrum, lying on the border of the outer and middle ear.

Auricle(auricula) - structural unit of the outer ear. The base of the auricle is represented by elastic cartilage covered with thin skin. The auricle is funnel-shaped with indentations and protrusions on the inner surface. Its free edge is curl(helix) - curved towards the center of the ear. Below and parallel to the helix is antihelix(anthelix), which ends at the bottom near the opening of the external auditory canal tragus(tragus). Posteriorly the tragus is located antitragus(antitragus). In the lower part of the auricle there is no cartilage and the skin forms a fold - lobe or ear lobule (lobulus auriculare). Above, behind and below, rudimentary striated muscles are attached to the cartilaginous part of the external auditory canal, which have actually lost their function, and displacement of the auricle does not occur.

External auditory canal(meatus acusticus externus) – structural formation of the outer ear. The outer third of the external auditory canal consists of cartilage (cartilago meatus acustici), related to the auricle; two-thirds of its length is formed by the bony part of the temporal bone. The external auditory canal has an irregular cylindrical shape. Opening on the side surface of the head, it is directed along the frontal axis into the depths of the skull and has two bends: one in the horizontal, the other in the vertical plane. This shape of the ear canal ensures that only sound waves reflected from its walls pass to the eardrum, which reduces its stretching. The entire ear canal is covered with thin skin, in the outer third of which there are hair and sebaceous glands (gll. cereminosae). The epithelium of the skin of the external auditory canal continues to the eardrum.

Eardrum(membrana tympani) - a formation located on the border of the outer and middle ear. The eardrum develops along with the organs of the outer ear. It is an oval, 11x9 mm in size, thin translucent plate. The free edge of this plate is inserted into tympanic sulcus(sulcus tympanicus) in the bony part of the ear canal. It is strengthened in the furrow by a fibrous ring, not along the entire circumference. On the side of the auditory canal, the membrane is covered with squamous epithelium, and on the side of the tympanic cavity with mucosal epithelium.

The basis of the membrane consists of elastic and collagen fibers, which in its upper part are replaced by fibers of loose connective tissue. This part is poorly stretched and is called pars flaccida. In the central part of the membrane, the fibers are arranged circularly, and in the anterior, posterior and lower peripheral parts - radially. Where the fibers are oriented radially, the membrane is stretched and shines in reflected light. In newborns, the eardrum is located almost transversely to the diameter of the external auditory canal, and in adults - at an angle of 45°. In the central part it is concave and is called navel(umbo membranae tympani), where the handle of the hammer is attached to the side of the middle ear .

Middle ear

The middle ear (auris media) is a structural formation of the hearing organ. Comprises tympanic cavity with those imprisoned in it auditory ossicles and auditory tube connecting the tympanic cavity with the nasopharynx.

Tympanic cavity

The tympanic cavity (cavum tympani) is a structural formation of the middle ear, located at the base of the pyramid of the temporal bone between the external auditory canal and the labyrinth (inner ear). It contains a chain of three small auditory ossicles that transmit sound vibrations from the eardrum to the labyrinth. The tympanic cavity has an irregular cuboid shape and a small size (volume about 1 cm3). The walls that limit the tympanic cavity border important anatomical structures: the inner ear, the internal jugular vein, the internal carotid artery, the cells of the mastoid process and the cranial cavity.

Anterior wall of the tympanic cavity(paries caroticus) - a wall close to the internal carotid artery. At the top of this wall is internal opening of the auditory tube(ostium tympanicum tubae anditivae), which gapes widely in newborns and young children, which explains the frequent penetration of infection from the nasopharynx into the middle ear cavity and further into the skull.

Membranous wall of the tympanic cavity(paries membranaceus) - lateral wall, formed by the eardrum and the bony plate of the external auditory canal. The upper, dome-shaped expanded part of the tympanic cavity forms supratympanic pocket(recessus epitympanicus), containing two bones: head of the malleus and incus. With the disease, pathological changes in the middle ear are most pronounced in the supratympanic recess.

Mastoid wall of the tympanic cavity(paries mastoideus) - posterior wall, delimits the tympanic cavity from the mastoid process. Contains a number of elevations and openings: pyramidal elevation(eminentia pyramidalis), which contains the stapes muscle (m. stapedius); projection of the lateral semicircular canal(prominentia canalis semicircularis lateralis); facial canal projection(prominentia canalis facialis); mastoid cave(antrum mastoideum), bordering the posterior wall of the external auditory canal.

The tegmental wall of the tympanic cavity(paries tegmentalis) - the upper wall, has a dome shape (pars cupularis) and separates the cavity of the middle ear from the cavity of the middle cranial fossa.

Jugular wall of the tympanic cavity(paries jugularis) - the lower wall, separates the tympanic cavity from the fossa of the internal jugular vein, where its bulb is located. In the posterior part of the jugular wall there is subulate protuberance(prominentia styloidea), a trace of pressure from the styloid process.

Auditory ossicles(ossicula auditus) - formations inside the tympanic cavity of the middle ear, connected by joints and muscles, providing air vibrations of varying intensity. The auditory ossicles include hammer, anvil and stirrup.

Hammer(malleus) – auditory ossicle. At the malleus they secrete neck(collum mallei) and handle(manubribm mallei). Hammer head(caput mallei) is connected by the incus-mallear joint (articulatio incudomallearis) to the body of the incus. The handle of the malleus fuses with the eardrum. And the muscle that stretches the eardrum (m. tensor tympani) is attached to the neck of the malleus.

Tensor tympani muscle(m. tensor tympani) is a striated muscle that originates from the walls of the muscular-tubal canal of the temporal bone and is attached to the neck of the malleus. By pulling the handle of the hammer inside the tympanic cavity, it strains the eardrum, so the eardrum is tense and concave into the cavity of the middle ear. Innervation of the muscle from the V pair of cranial nerves.

Anvil(incus) – auditory ossicle, has a length of 6-7 mm, consists of body(corpus incudis) and two legs: short (crus breve) and long (crus langum). The long leg bears a lenticular process (processus lenticularis) and is articulated by the incudostapedia joint with the head of the stapes (articulatio incudostapedia).

Stirrup(stapes) - auditory ossicle, has head ( caput stapedis), front and back legs(crura anterius et posterius) and base(basis stapedis). The stapedius muscle is attached to the posterior leg. The base of the stapes is inserted into the oval window of the vestibule of the labyrinth. The annular ligament (lig. anulare stapedis) in the form of a membrane located between the base of the stapes and the edge of the oval window ensures the mobility of the stapes when exposed to air waves on the eardrum.

Stapes muscle(m. stapedius) - a striated muscle, begins in the thickness of the pyramidal eminence of the mastoid wall of the tympanic cavity and is attached to the posterior leg of the stapes. Contracting, it brings the base of the stirrup out of the hole. Innervation from the VII pair of cranial nerves. During strong vibrations of the auditory ossicles, together with the muscle that stretches the eardrum, it holds the auditory ossicles, reducing their displacement.

Eustachian tube

The auditory tube (tuba auditiva), the Eustachian tube, is a formation of the middle ear that serves to allow air from the pharynx to enter the tympanic cavity, which maintains equal pressure on the outer and inner sides of the eardrum. The auditory tube consists of bone and cartilage parts that are connected to each other. Bone part(pars ossea), 6 - 7 mm long and 1 - 2 mm in diameter, is located in the temporal bone. Cartilaginous part(pars cartilaginea), made of elastic cartilage, has a length of 2.3 - 3 mm and a diameter of 3 - 4 mm, located in the thickness of the lateral wall of the nasopharynx.

Originate from the cartilaginous part of the auditory tube tensor palatine muscle(m. tensor veli palatini), velopharyngeal muscle(m. palatopharyngeus), muscle lifting the velum(m. levator veli palatini). Thanks to these muscles, when swallowing, the auditory tube opens and the air pressure in the nasopharynx and middle ear is equalized. The inner surface of the tube is covered with ciliated epithelium; in the mucous membrane there are mucous glands(gll. tubariae) and accumulation of lymphatic tissue. It is well developed and forms the tubal tonsil at the mouth of the nasopharyngeal opening of the tube.

Inner ear

The inner ear (auris interna) is a structural formation related to both the organ of hearing and the vestibular apparatus. The inner ear consists of bony and membranous labyrinths. These labyrinths form vestibule, three semicircular canals(vestibular apparatus) and snail related to the organ of hearing.

Snail(cochlea) is an organ of the auditory system, part of the bony and membranous labyrinth. The bony part of the cochlea consists of spiral channel(canalis spiralis cochleae), limited by the bone substance of the pyramid. The channel has 2.5 circular strokes. Located in the center of the cochlea hollow bone rod(modiolus), located in the horizontal plane. It protrudes into the lumen of the cochlea from the side of the rod. bony spiral plate(lamina spiralis ossea). In its thickness there are openings through which blood vessels and auditory nerve fibers pass to the spiral organ.

Spiral plate The cochlea, together with the formations of the membranous labyrinth, divides the cochlear cavity into 2 parts: staircase vestibule(scala vestibuli), connecting to the cavity of the vestibule, and staircase drum(scala tympani). The place where the scala vestibule transitions into the scala tympani is called lucid opening of the cochlea(helicotrema). The window of the cochlea opens into the scala tympani. The cochlear aqueduct originates from the scala tympani and passes through the bony substance of the pyramid. On the lower surface of the posterior edge of the pyramid of the temporal bone there is an external snail water pipe hole(apertura externa canaliculi cochleae).

Cochlear part the membranous labyrinth is represented cochlear duct(ductus cochlearis). The duct begins from the vestibule in the area cochlear recess(recessus cochlearis) of the bony labyrinth and ends blindly near the apex of the cochlea. In cross-section, the cochlear duct has a triangular shape, and most of it is located closer to the outer wall. Thanks to the cochlear duct, the cavity of the bony duct of the cochlea is divided into 2 parts: the upper one - the scala vestibule and the lower one - the scala tympani.

The outer (stria vascular) wall of the cochlear duct fuses with the outer wall of the bony duct of the cochlea. The upper (paries vestibularis) and lower (membrana spiralis) walls of the cochlear duct are a continuation of the bony spiral plate of the cochlea. They originate from its free edge and diverge towards the outer wall at an angle of 40 - 45°. On the bottom wall there is a sound-receiving apparatus - spiral organ(organ of Corti).

spiral organ(organum spirale) is located throughout the entire cochlear duct and is located on a spiral membrane, which consists of thin collagen fibers. Sensitive hair cells are located on this membrane. The hairs of these cells are immersed in a gelatinous mass called cover membrane(membrana tectoria). When a sound wave swells the basilar membrane, the hair cells standing on it sway from side to side and their hairs, immersed in the covering membrane, bend or stretch to the diameter of a hydrogen atom. These atom-sized changes in the position of the hair cells produce a stimulus that generates the generator potential of the hair cells.

One reason for the high sensitivity of hair cells is that the endolymph maintains a positive charge of about 80 mV relative to the perilymph. The potential difference ensures the movement of ions through the pores of the membrane and the transmission of sound stimuli. When electrical potentials were removed from different parts of the cochlea, 5 different electrical phenomena were discovered. Two of them - the membrane potential of the auditory receptor cell and the endolymph potential - are not caused by the action of sound; they are also observed in the absence of sound. Three electrical phenomena - the microphonic potential of the cochlea, the summation potential and the potentials of the auditory nerve - arise under the influence of sound stimulation.

The membrane potential of an auditory receptor cell is recorded when a microelectrode is inserted into it. As with other nerve or receptor cells, the inner surface of the auditory receptor membranes is negatively charged (-80 mV). Since the hairs of auditory receptor cells are washed by positively charged endolymph (+ 80 mV), the potential difference between the inner and outer surfaces of their membrane reaches 160 mV. The significance of a large potential difference is that it greatly facilitates the perception of weak sound vibrations. The endolymph potential, recorded when one electrode is inserted into the membranous canal and the other into the area of ​​the round window, is determined by the activity of the choroid plexus (stria vascularis) and depends on the intensity of oxidative processes. When breathing is impaired or tissue oxidative processes are suppressed by cyanide, the endolymph potential decreases or disappears. If you insert electrodes into the cochlea, connect them to an amplifier and a loudspeaker and apply sound, the loudspeaker accurately reproduces this sound.

The described phenomenon is called the cochlear microphone effect, and the recorded electrical potential is called the cochlear microphone potential. It has been proven that it is generated on the hair cell membrane as a result of hair deformation. The frequency of microphone potentials corresponds to the frequency of sound vibrations, and the amplitude, within certain limits, is proportional to the intensity of sounds acting on the ear. In response to strong sounds of high frequency, a persistent shift in the initial potential difference is noted. This phenomenon is called summation potential. As a result of the occurrence of microphonic and summation potentials in the hair cells under the influence of sound vibrations on them, pulsed excitation of the auditory nerve fibers occurs. The transfer of excitation from the hair cell to the nerve fiber occurs, apparently, both electrically and chemically.

The olfactory analyzer plays a significant role in the life of animals and humans, informing the body about the state of the environment, monitoring the quality of food and inhaled air.

The first receptor neurons of the olfactory analyzer pathway (tractus olfactorius) are bipolar cells embedded in the mucous membrane of the olfactory region of the nasal cavity (the area of ​​the superior turbinate and the corresponding part of the nasal septum).

Their short peripheral processes end in a thickening - the olfactory club, which carries on its free surface a varying number of cilia-like outgrowths (olfactory hairs), significantly increasing the surface of interaction with molecules of odorous substances and transforming the energy of chemical irritation into a nerve impulse.

The central processes (axons), uniting with each other, form 15-20 olfactory filaments, which together make up the olfactory nerve. The olfactory filaments penetrate the cranial cavity through the cribriform plate of the ethmoid bone and approach the olfactory bulb, where the second neurons are located. The axons of the second neurons go as part of the olfactory tract, the olfactory triangle and the anterior perforated substance of their own and opposite sides, the subcallosal gyrus and the septum pellucidum. The bodies of the third neurons are located here. Their axons follow to the cortical end of the olfactory analyzer - the uncus of the parahypocampal gyrus and the ammonian horn, where the bodies of the fourth neurons are located (Fig. 34).

Pathways for skin sensitivity

Skin sensitivity includes sensations of pain, temperature, touch, pressure, etc.

Pathway of pain and temperature sensitivity

The beginning of the path is the skin receptor, the end is the cells of the fourth layer of the cortex of the postcentral gyrus.

The path is crossed, the cross is segment-by-segment in the spinal cord. Signals of pain and temperature are carried along the lateral spinothalamic tract (tractus spinothalamicus lateralis).

Rice. 34. Conducting path of the olfactory analyzer

(Yu.A. Orlovsky, 2008).

The body of the first neuron is a pseudounipolar nerve cell of the spinal ganglion. The dendrite goes to the periphery as part of the spinal nerve and ends with a specific receptor. The axon of the first neuron passes as part of the dorsal root to the nuclei of the dorsal horn of the spinal cord. The second neurons are located here (in the proper nuclei of the dorsal horn). The axon of the second neuron passes to the opposite side and rises in the lateral cord of the spinal cord as part of the lateral spinothalamic tract to the medulla oblongata, where it participates in the formation of the medial lemniscus. The fibers of the latter follow through the bridge, the cerebral peduncles to the lateral nuclei of the visual thalamus, where the third neurons of the pathway of pain and temperature sensitivity are located. The axon of the third neuron passes through the internal capsule and ends on the cells of the cortex of the postcentral gyrus (thalamocortical tract). This is the fourth neuron of the pain and temperature sensitivity pathway (Fig. 35).