Olfactory pathways in the brain. Meaning of the olfactory tract in medical terms. See what the "Olfactory tract" is in other dictionaries
The olfactory analyzer ensures the perception of olfactory stimuli, the conduction of nerve impulses to the olfactory centers, the analysis and integration of the information received in them.
Olfactory receptors are located in olfactory region of the nasal mucosa and represent peripheral processes of olfactory cells (Fig. 1). The olfactory cells themselves are the bodies of the first neuron of the olfactory analyzer(Fig. 2, 3).
Rice. 1. (stained area of the mucous membrane of the lateral wall of the nasal cavity and nasal septum): 1 - olfactory bulb (bulbus olfactorius); 2 - olfactory nerves (nn. olfactorii; lateralis); 3 - olfactory tract (tractus olfactorius); 4 - superior nasal concha (concha nasalis superior); 5 - olfactory nerves (nn. olfactorii; medialis); 6 - nasal septum (septum nasi); 7 - lower nasal concha (concha nasalis inferior); 8 - middle nasal concha (concha nasalis media).
Rice. 2.: R - receptors - peripheral processes of sensitive cells of the mucous membrane of the olfactory region of the nasal cavity; I - the first neuron - sensitive cells of the mucous membrane of the olfactory region of the nasal cavity; II - the second neuron - mitral cells of the olfactory bulb (bulbus olfactorius); III - the third neuron - cells of the olfactory triangle, the anterior perforated substance and the nuclei of the transparent septum (trigonum olfactorium, septum pellucidum, substantia perforata anterior); IV - cortical end of the olfactory analyzer - cells of the cortex of the hook and parahippocampal gyrus (uncus et gyrus parahippocampalis); 1 - olfactory region of the nasal cavity (pars olfactoria tunicae mucosae nasi); 2 - olfactory nerves (nn. olfactorii); 3 - olfactory bulb; 4 - olfactory tract and its three bundles: medial, intermediate and lateral (tractus olfactorius, stria olfactoria lateraris, intermedia et medialis); 5 - short way - to the cortical end of the analyzer; 6 - the middle path - through the plate of the transparent septum, the arch and fringe of the seahorse to the bark; 7 - a long way - over the corpus callosum as part of the cingulate bundle; 8 - mammillary bodies and the path from them to the thalamus (fasciculus mamillothalamicus); 9 - nuclei of the thalamus; 10 - upper mounds of the midbrain and the path to them from the mastoid bodies (fasciculus mamillotegmentalis).
Rice. 3. .
The central processes of the olfactory cells make up the olfactory nerves (nn. olfactorii), which penetrate the cranial cavity through the openings of the cribriform plate (lamina cribrosa) of the ethmoid bone. The olfactory nerves go to the olfactory bulb and come into contact with the mitral cells olfactory bulb (bodies of the second neuron).
The axons of the second neurons are in the composition olfactory tract, are divided into the medial bundle - to the olfactory bulb of the opposite side, the lateral bundle - to the cortical end of the analyzer and the intermediate bundle, which approaches the bodies of the third neurons. Bodies of third neurons located in olfactory triangle, nuclei of the transparent septum and the anterior perforated substance.
The axons of the third neurons are sent to the cortical end of the olfactory analyzer in three ways: from the cells in the olfactory triangle, a long path above the corpus callosum, from the nuclei of the transparent septum there is a middle path through the fornix, and from the anterior perforated substance, a short path leads immediately to the hook.
The long path provides olfactory associations, the average search for the source of the odor, and the short motor protective reaction to a pungent odor. The cortical end of the olfactory analyzer is located in the hook and parahippocampal gyrus.
A feature of the olfactory analyzer is that nerve impulses initially enter the cortex, and then from the cortex to the subcortical centers: the papillary bodies and the anterior nuclei of the thalamus, interconnected by the papillary-thalamic bundle.
The subcortical centers, in turn, are connected with the cortex of the frontal lobes, the motor centers of the extrapyramidal system, the limbic system and the reticular formation, providing emotional reactions, protective motor reactions, changes in muscle tone, etc. in response to olfactory stimuli.
Development of the olfactory organ
The anlage of the olfactory organ occupies the most anterior edge of the neural plate. Then the anlage of the peripheral part of the olfactory analyzer is separated from the CNS rudiment and moves to the olfactory part of the developing nasal cavity. In the fourth month of the intrauterine period of development in the olfactory part, the cells differentiate into supporting and olfactory. The processes of the olfactory cells grow through the still cartilaginous cribriform plate (lamina cribrosa) into the olfactory bulb. This is how the secondary connection of the olfactory organ with the central nervous system occurs.
Anomalies in the development of the olfactory organ
- Arynencephaly is the absence of the central and peripheral parts of the olfactory brain.
- Olfactory nerve defects.
- Weakening, lack of olfactory perception.
In diseases of the mucous membrane of the nasal cavity, tumors of the base of the brain and the frontal lobe, a pathological decrease in the sense of smell is noted ( hyposmia) or its complete loss ( anosmia). In allergic conditions, an exacerbation of the sense of smell is possible ( hyperosmia).
Sources and literature
- Kondrashev A.V., O.A. Kaplunov. Anatomy of the nervous system. M., 2010.
The olfactory analyzer plays a significant role in the life of animals and humans, informing the body about the state of the environment, controlling 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 region of the superior turbinate and the corresponding part of the nasal septum).
Their short peripheral processes end in a thickening - an olfactory club, carrying on its free surface a different number of ciliary-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) combine with each other to form 15-20 olfactory filaments, which together make up the olfactory nerve. The olfactory filaments penetrate the cranial cavity through the ethmoid 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 transparent septum. The bodies of the third neurons are laid here. Their axons follow to the cortical end of the olfactory analyzer - the hook of the parahypocampal gyrus and the ammon horn, where the bodies of the fourth neurons are located (Fig. 34).
Ways of carrying out skin sensitivity
Skin sensitivity includes the feeling 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 segmented in the spinal cord. Pain and temperature signals are conducted along the lateral spinothalamic tract (tractus spinothalamicus lateralis).
Rice. 34. Conductive path of the olfactory analyzer
(Yu.A. Orlovsky, 2008).
The body of the first neuron is a pseudo-unipolar 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 posterior root to the nuclei of the posterior horn of the spinal cord. The second neurons are located here (in the own nuclei of the posterior horn). The axon of the second neuron passes to the opposite side and rises in the lateral funiculus of the spinal cord as part of the lateral spinothalamic tract to the oblong, where they participate in the formation of the medial loop. The fibers of the latter follow through the bridge, the legs of the brain to the lateral nuclei of the visual tubercle, 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).
The pathways of the olfactory analyzer (tractus olfactorius) have a complex structure. The olfactory receptors of the mucous membrane of the nasal cavity perceive changes in the chemistry of the air environment and are the most sensitive in comparison with the receptors of other sense organs. First neuron formed by bipolar cells located in the mucous membrane of the superior nasal concha 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 holes of the cribriform plate into the cranial cavity, and switch 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 sent to different brain structures. Outer beam, rounding the lateral sulcus of the large brain, 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 g hippocampus and hook; the other part of the medial bundle forms olfactory-lead bundle nerve fibers that run through brain strips(stria medullaris) of the thalamus of its own side. The olfactory-leading bundle ends in the nuclei of the triangle of the frenulum of the suprathalamic region, where the descending path begins, connecting the motor neurons of the spinal cord. Kernels of the triangular bridle duplicated by a second system of fibers coming from the mastoid bodies.
The olfactory system has not undergone a drastic restructuring in the course of evolution and has no representation in the neocortex.
auditory sensory system
auditory system , auditory analyzer - a set of mechanical, receptor and nervous structures that perceive and analyze sound vibrations. The structure of the auditory system, especially its peripheral part, may vary in different animals. So, 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. Amphibians, reptiles, and birds develop additional receptor cells (basilar papilla) in the inner ear. In higher vertebrates, including most mammals, the auditory system consists of the outer, middle, and inner ear, the auditory nerve, and series-connected nerve centers (the main ones are the cochlear and superior olive nuclei, the posterior colliculus, and the auditory cortex).
The development of the central part of the auditory system depends on environmental factors, on the importance of the auditory system in the behavior of animals. The auditory nerve fibers run 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, the cochlear septum plays a significant role - a kind of mechanical spectral analyzer that functions as a series of mutually mismatched filters spatially scattered along the cochlear septum, the oscillation 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 the sound, etc. The neurons of the central, especially the higher parts of the auditory system, selectively respond to complex features of sounds (for example, to a certain frequency of amplitude modulation, to the direction of frequency modulation and movement of sound ).
The auditory analyzer includes the organ of hearing, the pathways of auditory information and the central representation in the cerebral cortex.
hearing organ
Organ of hearing (organa audites) - labyrinth, which contains two kinds of receptors: one of them (organ of Corti) serve to perceive sound stimuli, others represent perceiving devices stato-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 the labyrinth in this sense can be a static vesicle (oto- or statocyst), which is very common among invertebrate animals living in water, such as molluscs. In vertebrates, this initially simple form of the vesicle becomes much more complicated as the functions of the labyrinth become more complex.
Genetically, the vesicle originates from the ectoderm by invagination followed by lacing, then the tubular appendages of the static apparatus - the semicircular canals - begin to separate. Myxines 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, due to which they are able to move the body in two directions. Starting with fish, all other vertebrates develop 3 semicircular canals corresponding to the three dimensions of space that exist in nature, allowing them to move in all directions.
As a result, labyrinth vestibule and semicircular canals having a special nerve - n. vestibularis. With access to land, with the appearance in land animals of locomotion with the help of limbs, and in humans - upright walking, the value 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 aquatic environment to the air, a sound-conducting apparatus is attached to the inner ear. Starting with amphibians, appears middle ear- tympanic cavity with tympanic membrane and auditory ossicles. The acoustic apparatus reaches its highest development in mammals that 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 deep ear canal and auricle.
Auricle represents a later acquisition, playing the role of a horn for amplifying sound, and also serving to protect the external auditory canal. In terrestrial mammals, the auricle is equipped with special muscles and easily moves in the direction of sound. In mammals leading aquatic and underground lifestyles, it is absent; 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 are part of the second signaling system.
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 cerebral bladder, an auditory vesicle appears from the ectoderm - the rudiment of the labyrinth. By the end of 4 weeks, a blind passage (ductus endolymphaticus) and 3 semicircular canals grow out of 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 of origin of the endolymphatic duct 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 course of the cochlea (ductus cochlearis). Initially, the walls of the vesicle cavity, in connection with the ingrowth of the peripheral processes of nerve cells from the auditory ganglion lying on the front side of the labyrinth, turns into sensitive cells (the organ of Corti). The mesenchyme adjacent to the membranous labyrinth turns into a connective tissue that creates around the formed utriculus, sacculus and semicircular canals into perilymphatic spaces. At 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 by perichondral ossification, repeating the general form of the membranous.
Middle ear- the tympanic cavity with the auditory tube - develops from the first pharyngeal pocket and the lateral part of the upper pharyngeal wall, 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 (hammer and anvil) and second (stapes) visceral arches. The outer ear develops from the first gill pocket.
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, her cartilage begins to harden. The external auditory canal in a newborn is short and wide, and the bone part consists of a bone ring. The size of the eardrum in a newborn and an adult is almost the same. The tympanic membrane 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 up to 2-3 years old, 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 is connected by a wide opening with the cells of the mastoid process. The auditory ossicles, although containing 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 tympanic membrane, together with it vibrate the handle of the malleus, which displaces all the auditory ossicles. The base of the stirrup 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 advances through the opening at the top of the cochlea (helicotrema) into the scala tympani. Its liquid stretches the secondary membrane that closes 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 sensitive cells. The sensitive cells are in contact with the first sensitive neuron.
outer ear
The outer ear (auris externa) is a structural formation of the hearing organ, which includes Auricle, external auditory meatus and tympanic membrane 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 has a funnel-shaped shape with recesses and protrusions on the inner surface. Her free edge - curl(helix) - bent to the center of the ear. Below and parallel to the curl is antihelix(anthelix), which ends at the bottom near the opening of the external auditory meatus tragus(tragus). Behind the tragus is located antitragus(antitragus). In the lower part of the auricle does not contain cartilage and the skin forms a fold - lobe or ear lobe (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 the auricle does not move.
External auditory canal(meatus acusticus externus) - structural formation of the outer ear. The outer third of the external auditory meatus 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 meatus has an irregular cylindrical shape. Opening on the lateral 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 form of the ear canal ensures that only sound waves reflected from its walls pass to the tympanic membrane, which reduces its stretching. The entire auditory meatus 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 passes to the tympanic membrane.
Eardrum(membrana tympani) - a formation located on the border of the outer and middle ear. The tympanic membrane develops along with the organs of the outer ear. It is an oval, 11x9 mm, thin translucent plate. The free edge of this plate is inserted into tympanic sulcus(sulcus tympanicus) in the bone part of the ear canal. It is strengthened in the furrow by the fibrous ring, not along the entire circumference. On the side of the ear canal, the membrane is covered with a squamous epithelium, and on the side of the tympanic cavity with an epithelium of the mucous membrane.
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 loosely stretched and is called the pars flaccida. In the central part of the membrane, the fibers are arranged circularly, and in the anterior, posterior and lower peripheral parts of it - radially. Where the fibers are oriented radially, the membrane is stretched and glistens in reflected light. In newborns, the tympanic membrane 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 malleus is attached from the side of the middle ear .
Middle ear
The middle ear (auris media) is a structural formation of the organ of hearing. Comprises tympanic cavity with the enclosed ossicles and auditory tube, which communicates the tympanic cavity with the nasopharynx.
tympanic cavity
The tympanic cavity (cavum tympani) is a structural formation of the middle ear, laid at the base of the pyramid of the temporal bone between the external auditory meatus and the labyrinth (inner ear). It contains a chain of three small auditory ossicles that transmit sound vibrations from the tympanic membrane to the labyrinth. The tympanic cavity has an irregular cuboid shape and a small size (about 1 cm 3 in volume). The walls limiting the tympanic cavity border on important anatomical formations: 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 closely adjacent 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) - the lateral wall, formed by the tympanic membrane and the bone plate of the external auditory canal. The upper, dome-shaped expanded part of the tympanic cavity forms epitympanic pocket(recessus epitympanicus), containing two bones: malleus head and anvil. With the disease, pathological changes in the middle ear are most pronounced in the epitympanic pocket.
Mastoid wall of the tympanic cavity(paries mastoideus) - the back wall, delimits the tympanic cavity from the mastoid process. Contains a series of elevations and openings: pyramidal eminence(eminentia pyramidalis), which contains the stirrup muscle (m. stapedius); projection of the lateral semicircular canal(prominentia canalis semicircularis lateralis); protrusion of the facial canal(prominentia canalis facialis); mastoid cave(antrum mastoideum), bordering the posterior wall of the external auditory canal.
Tire wall of the tympanic cavity(paries tegmentalis) - the upper wall, has a domed shape (pars cupularis) and separates the middle ear cavity 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 back of the jugular wall there is styloid protrusion(prominentia styloidea), a trace of the pressure of 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 are hammer, anvil and stirrup.
Hammer(malleus) - auditory ossicle. The malleus secretes neck(collum mallei) and handle(manubribm mallei). Hammer head(caput mallei) is connected by an anvil-hammer joint (articulatio incudomallearis) with the body of the anvil. The handle of the malleus fuses with the tympanic membrane. And a muscle is attached to the neck of the malleus, which stretches the eardrum (m. tensor tympani).
Muscle that stretches the tympanic membrane(m. tensor tympani) - a striated muscle, originates from the walls of the musculo-tubal canal of the temporal bone and is attached to the neck of the malleus. Pulling the handle of the malleus inside the tympanic cavity, strains the tympanic membrane, so the tympanic membrane is tense and concave into the cavity of the middle ear. Innervation of the muscle from the fifth 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 the lenticular process (processus lenticularis), articulates with the head of the stirrup (articulatio incudostapedia) by the anvil-stapes joint.
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 back leg. The stirrup base is inserted into the oval window of the labyrinth vestibule. The annular ligament (lig. anulare stapedis) in the form of a membrane located between the base of the stirrup and the edge of the oval window ensures the mobility of the stirrup when air waves act on the eardrum.
stirrup 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 back leg of the stirrup. Contracting, removes the base of the stirrup from the hole. Innervation from the VII pair of cranial nerves. With strong vibrations of the auditory ossicles, together with the muscle that stretches the eardrum, it holds the auditory ossicles, reducing their displacement.
auditory trumpet
The auditory tube (tuba auditiva), the Eustachian tube, is the formation of the middle ear, which serves to access air from the pharynx into the tympanic cavity, which maintains the same pressure on the outer and inner sides of the tympanic membrane. The auditory tube consists of bone and cartilage parts that are interconnected. 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.
From the cartilaginous part of the auditory tube originate tensor palatine muscle(m. tensor veli palatini), palatopharyngeal muscle(m. palatopharyngeus), muscle lifting the veil of the sky(m. levator veli palatini). Thanks to these muscles, when swallowing, the auditory tube opens and the air pressure in the nasopharynx and middle ear equalizes. The inner surface of the tube is covered with ciliated epithelium; in the mucosa are mucous glands(gll. tubariae) and accumulation of lymphatic tissue. It is well developed and forms a 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 is made up of bony and membranous labyrinths. These labyrinths form vestibule, three semicircular canals(vestibular apparatus) and snail relating to the organ of hearing.
Snail(cochlea) - an organ of the auditory system, is part of the bone and membranous labyrinth. The bony part of the cochlea is made up 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 shaft(modiolus), located in the horizontal plane. In the lumen of the cochlea from the side of the rod is issued bony spiral plate(lamina spiralis ossea). In its thickness there are holes through which blood vessels and fibers of the auditory nerve pass to the spiral organ.
spiral plate The cochlea, together with the formations of the membranous labyrinth, divides the cochlear cavity into 2 parts: vestibule stairs(scala vestibuli), which connects to the cavity of the vestibule, and drum ladder(scala tympani). The place where the scala vestibule passes into the scala tympani is called clarified hole of the cochlea(helicotrema). A snail window opens into the drum stairs. From the scala tympani originates the aqueduct of the cochlea, passing through the bone substance of the pyramid. On the lower surface of the posterior edge of the pyramid of the temporal bone is the outer snail plumbing hole(apertura externa canaliculi cochleae).
cochlear part membranous labyrinth is represented cochlear duct(ductus cochlearis). The duct starts from the vestibule in the area cochlear cavity(recessus cochlearis) of the bony labyrinth and ends blindly near the top of the cochlea. On a transverse section, the cochlear duct has a triangular shape, and most of it is located closer to the outer wall. Thanks to the cochlear passage, the cavity of the bony passage of the cochlea is divided into 2 parts: the upper one - the scala vestibule and the lower one - the scala tympani.
The outer (vascular strip) wall of the cochlear duct fuses with the outer wall of the cochlear osseous tract. 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 is a sound-receiving apparatus - spiral organ(organ of Corti).
spiral organ(organum spirale) is located throughout the cochlear duct and is located on a spiral membrane, which consists of thin collagen fibers. Sensory hair cells are located on this membrane. The hairs of these cells are immersed in a gelatinous mass called integumentary 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 integumentary membrane, bend or stretch to the diameter of a hydrogen atom. These atom-sized changes in the position of hair cells produce a stimulus that generates a hair cell generator potential.
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 diverting electrical potentials from different parts of the cochlea, 5 different electrical phenomena were found. Two of them - the membrane potential of the auditory receptor cell and the potential of the endolymph - are not caused by the action of sound, they are also observed in the absence of sound. Three electrical phenomena - the microphone potential of the cochlea, the summation potential and the potentials of the auditory nerve - arise under the influence of sound stimuli.
The membrane potential of the auditory receptor cell is recorded when a microelectrode is introduced into it. As well as in other nerve or receptor cells, the inner surface of the membranes of auditory receptors is negatively charged (-80 mV). Since the hairs of the auditory receptor cells are washed by positively charged endolymph (+ 80 mV), the potential difference between the inner and outer surface of their membrane reaches 160 mV. The significance of a large potential difference lies in the fact that it greatly facilitates the perception of weak sound vibrations. The potential of the endolymph, recorded when one electrode is inserted into the membranous canal, and the other into the region of the round window, is due to the activity of the choroid plexus (stria vascularis) and depends on the intensity of oxidative processes. With respiratory disorders or suppression of tissue oxidative processes by cyanides, the potential of the endolymph drops or disappears. If you insert electrodes into the cochlea, connect them to an amplifier and a loudspeaker, and act on sound, then the loudspeaker accurately reproduces this sound.
The described phenomenon is called the cochlear microphone effect, and the recorded electric 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 the summation potential. As a result of the appearance in the hair cells under the action of sound vibrations of the microphone and summation potentials, impulse excitation of the fibers of the auditory nerve occurs. The transfer of excitation from the hair cell to the nerve fiber occurs, apparently, both electrically and chemically.
BNA, JNA) part of the olfactory brain in the form of a thin cord located on the lower surface of the frontal lobe of the cerebral hemisphere between the olfactory bulb and the olfactory triangle.
1. Small medical encyclopedia. - M.: Medical Encyclopedia. 1991-96 2. First aid. - M.: Great Russian Encyclopedia. 1994 3. Encyclopedic dictionary of medical terms. - M.: Soviet Encyclopedia. - 1982-1984.
See what the "Olfactory tract" is in other dictionaries:
- (tractus olfactorius, PNA, BNA, JNA) part of the olfactory brain in the form of a thin cord located on the lower surface of the frontal lobe of the cerebral hemisphere between the olfactory bulb and the olfactory triangle ... Big Medical Dictionary
Schemes ... Wikipedia
Scheme of the olfactory brain The olfactory brain (lat. rhinencephalon) is a set of a number of structures of the telencephalon associated with the sense of smell ... Wikipedia
Olfactory brain- - the brain area responsible for the neuropsychology of odor perception: the olfactory bulb, olfactory tract, piriformis zone, parts of the piriform cortex and the amygdala complex ... Encyclopedic Dictionary of Psychology and Pedagogy
OLFATIVE BRAIN- Area of the brain responsible for the perception of smells. It includes the olfactory bulb, olfactory tract, piriformis, parts of the piriform cortex, and parts of the amygdala complex... Explanatory Dictionary of Psychology
- (tractus olfactomesencephalicus; L. Edinger, 1855 1918, German neurologist; A. Wallenberg, 1862 1949, German neuropathologist) a bundle of nerve fibers connecting the olfactory tract and the olfactory triangle with the nuclei of the hypothalamus, mastoid bodies, ... ... Big Medical Dictionary
Brain structures that were associated with the olfactory analyzer in the early stages of evolution. The olfactory brain consists of the olfactory bulb, olfactory tract, olfactory triangle, anterior perforated substance, ... ... medical terms
olfactory brain- (rhinencephalon) the most ancient part of the cerebral hemispheres, divided into peripheral and central sections. The peripheral section is located on the lower surface of the frontal lobe and includes the olfactory tract with the olfactory bulb, ... ... Glossary of terms and concepts on human anatomy
BRAIN OFLATIVE- (rhinencephalori) structures of the brain, which in the early stages of evolution were associated with the olfactory analyzer. The olfactory brain consists of the olfactory bulb, olfactory tract, olfactory triangle, anterior ... ... Explanatory Dictionary of Medicine
cranial nerves- Olfactory nerve (n. olfactorius) (I pair) refers to the nerves of special sensitivity. It starts from the olfactory receptors of the nasal mucosa in the superior nasal concha. Represents 15 20 thin nerve threads, ... ... Atlas of human anatomy
Brain- (encephalon) (Fig. 258) is located in the cavity of the brain skull. The average weight of the adult brain is approximately 1350 g. It has an ovoid shape due to the protruding frontal and occipital poles. On the outer convex upper lateral ... ... Atlas of human anatomy
Molecules of odorous substances, having previously been dissolved in the secretion of the olfactory glands, interact with the receptor proteins of the cilia, which causes a nerve impulse that travels along the axons of the olfactory neurons, which unite in small groups of 10-100 axons and pass through the ethmoid bone, reaching the olfactory bulb. There they form glomeruli, or glomeruli, which in turn form synapses with mitral and crested cells (the second neurons of the olfactory pathway). At the same time, the number of mitral and crested cells is much less than the number of axons of the first neurons of the olfactory pathway. This is explained by the fact that axons converge into groups before the formation of glomeruli (the number of glomeruli is less than the number of axons), and then the glomeruli join into groups before synapsing with mitral cells. For example, in rabbits, 26,000 axons of olfactory neurons converge into 200 glomeruli, which then converge in a ratio of 25:1 for each mitral cell. Due to the fact that axons coming from cells with the same receptors connect into glomeruli, such convergence increases the strength of the signal entering the brain. The axons of the second neurons of the olfactory tract form the olfactory tract, which passes into the olfactory triangle (see Fig. 3). Then the olfactory triangle leads to the bodies of the third neurons, to the transparent septum and perforated substance.
The olfactory analyzer is directly connected to the limbic system. This explains the presence of significant emotional component in olfactory perception. The smell can cause a feeling of pleasure or disgust, while changing the state of the body. In addition, the importance of olfactory stimuli in the regulation of sexual behavior should not be underestimated. Animal experiments have shown that the neuronal responses of the olfactory tract can be altered by injection of testosterone. Thus, the excitation of olfactory neurons is under the influence of sex hormones.
STRUCTURE OF THE TASTE ANALYZER
The taste analyzer carries information about the nature and concentration of substances entering the oral cavity.
Taste buds are located on the surface of the tongue. The length of taste buds is from 20 to 495 microns. Together with supporting cells in groups of 40-60 elements, they form taste buds in the epithelium of the papillae of the tongue. Large papillae, surrounded by a roller (they are called trough-shaped), at the base of the tongue form clusters of up to 200 taste buds each, smaller mushroom-shaped and foliate papillae on the anterior and lateral surfaces contain only a few buds. Humans have several thousand taste buds. The glands between the papillae secrete a fluid that flushes out the taste buds. The taste bud is flask-shaped, its length and width are about 70 microns. The distal parts of the receptor cells that make up the taste buds form microvilli in the amount of 30-40, which open into a common chamber, which communicates with the external environment through a pore on the surface of the papilla. Taste molecules reach the taste buds by passing through this pore. Taste buds are replaced very quickly; their life span is 10 days, after which new receptors are formed from the basal cells.
TASTE MAP OF THE LANGUAGE. TASTE QUALITIES
Taste sensitivity in humans
A person distinguishes 4 main taste qualities - sweet, sour, bitter and salty
Table 5. Characteristic taste qualities and their effectiveness in humans
Salts such as potassium chloride, for example, cause both bitter and salty sensations. Similar mixed feelings are also characteristic of many natural taste stimuli. For example, an orange has a sweet and sour taste, while a grapefruit has a bittersweet and sour taste.
Areas can be distinguished on the surface of the tongue specific sensitivity. The taste of bitter is felt at the base of the tongue, the tip of the tongue is sweet, the sides of the tongue are sour and salty with areas overlapping.
Between the chemical properties of a substance and his taste there is no dependency. For example, not only sugars, but also lead salts have a sweet taste, and the sweetest substances are artificial sugar substitutes (saccharin). The taste of a substance also depends on its concentration. Table salt in small quantities seems sweet. Sensitivity to bitter substances is noticeably higher, tk. such substances are often poisonous, and due to their high sensitivity we are warned of their presence in water or food, even if they are there in negligible concentrations.
