ChemistryreceptorIt is to feel inside and outside the bodyEnvironmental chemistryThe general term for stimulus receptors.Chemoreceptors are mostly distributed in nasal cavity and oral mucosa, tongue, eye conjunctivagenitalsMucosa, visceral wall, perivascular andnervous systemSome parts.
Chinese name
Chemoreceptor
Features
Feel the chemical stimulation of the internal and external environment of the body
The earliest animals on the earth lived in the ocean. When the composition of seawater changed significantly, it could directly affect the survival of the organism.So the chemoreceptorsBiological evolutionChina developed earlier.Unicellular animalIt shows thatChemotaxisBehavior.Amoeba、parameciumBoth show activities that tend to food and avoid harmful substances.coelenterateasHydraOfCoelomAnd the front end of the body has a chemosensory structure, which is generally low-grade aquaticCrustaceaMost of them have sensitive chemoreceptors on the body surface. All kinds of fish have developed chemoreceptors. In addition to the mouth and nose, there are also many chemoreceptors on both sides of the body.Terrestrial insects are very sensitive to chemical stimuli in the air. They are located around their mouths, on both sides of their bodies, on their antennae, legs andOvulatory foramenThere are chemoreceptors everywhere.Higher animals living in the air, because their body surface is wrapped with thick skin, their chemoreceptors are mostly concentrated in the skin or mucous membrane of the mouth, nose and face, of whichTaste receptorandOlfactory receptorIs more developed.
Main principles
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Chemoreceptors play a guiding role in animal behavior. Animals' activities such as feeding, avoiding harm, choosing habitat, finding host, "social" communication, courtship, etc. generally rely on the information received by chemical receptors.
Chemoreceptor
To feel chemical stimulation asSuitable stimulation, and the resulting centringNerve impulseThe receptor of.Although taste receptors and olfactory receptors are chemical receptors, they are difficult to correspond to taste and smell in many cases.Strictly speaking, coelenterates and other whole individuals are scattered (mostly hairy) primarySensory cellThey are chemoreceptors, but it is difficult to identify them one by one.In worms, these receptors gather to form sensory buds.PlanarianClassPolychaete, a pair at the front end of the bodyCiliated sulcusIt can also be regarded as the sameDevelopment stage。snail、SlugsTentacles and waterGastropodsThe coat hypertrophy seen near this gill（Olfactometer）The chemoreceptors are densely distributed, which seems to be at least equivalent to telesensory chemoreceptors.CrustaceaThe sensory hairs of the antennae andchitinThe cone (Chitinkegel) is also included in the chemoreceptor;In addition, chemoreceptors can also be seen in oral organs and the mouth.Spiders, use food firstTarsal ganglionOrgan touch test, then feel with clamp angle, finally bite and use mouthInternal receptorPerception;andAcari, forelimbTibiaHaller's or gan is a chemoreceptor.EchinodermaSpines (especiallyForked spine）Although it shows the sensitivity to chemical stimuli, the receptors are not clear.Insects and vertebrates, with the differentiation of smell and taste, have more developed structures of the two receptors.In addition, there are less specific chemoreceptors - common chemoreceptors, which also play an important role in higher animals.
Function
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Chemoreceptor, inAnimal behaviorIt has a guiding role. Animals' activities such as feeding, avoiding harm, choosing habitat, looking for host, "social" communication, courtship, etc. generally rely on chemical receptors to receive information.Smell is an important sense for humans and animals to recognize the environment, especiallyGregarious animalIt can often be used to identify enemies and friends, find nests, remember the way home, chase prey, escape harm, and find spouses.In identifying food and exploring the synergistic activities of olfactory receptors and taste receptors in toxic substances.
Human distribution
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The chemical receptors of the human body include those of taste, smell, artery and gastrointestinal tract.
Taste receptor
The taste receptors of various animals are mostly located in the front of the head, mouth and tongue because of their role in guiding feeding activities.In addition to the mouth, fish also have taste receptors in the skin around the mouth and on both sides of the body.insectDue to the special way of foraging, there are scattered taste receptors in all parts of the body, as well as in the mouth, antennae, legs and other places.stayAnimal evolutionTaste receptors play an important role in the discrimination between food and harmful substances in the environment.Higher animalThe taste receptor of the stomach is an important sensory device for various digestive reflex activities.
In humans and other higher animals, taste receptors are relatively concentrated, mainly distributed in the back of the tongue and the mucosa on both sides, and a small part is scattered in the mucosa of the pharynx and the back of the mouth.
Human taste receptorBasic structureIt's a taste bud, mostly concentrated on the tonguepapillaMedium.According to the shape of nipple, it can be divided into:Contoured nippleIt is located at the back of the tongue in the shape of a man, with a number of contours. The top of the nipple is disc shaped, surrounded by groovesMarginal partThere are multiple taste buds.Fungiform papilla, round mushroom shaped, small and flat, mostly on the back and sides of the tongue,Dorsum linguaeIt is widely distributed, and there are fewer taste buds in the fungiform papilla.Filamentous papilla, slender, distributed on both sides of the tongue, with a few taste buds and scatteredTaste cell。Another is calledLobular papilla, distributed on both sides of the posterior part of the tongue, in a folded shape.
LingualInnervationFrom 7th and 9thCerebral nerveThe anterior 2/3 of the tongue is composed ofChordae tympaniNerve innervation.The last 1/3 is composed ofGlossopharyngeal nerve(the 9th cranial nerve).The taste receptors distributed on the dorsal and bilateral edges of the anterior part of the tongue mainly receive sweet and salty stimuli;Distributed at the back of the tongue, it mainly receives acid and bitter stimulation.
The basic structure of taste receptors The taste bud consists of 30 to 80 cells of various types, most of which havemicrovilliThe cells are long spindle shaped, and the microvilli end extends to the mouth of the taste bud（Flavorhole）。There is afferent near the bottom of the cellNerve endingsFormation of bothSynapseType connection.ReceptivityThe cells are generally called flavor cells and can be divided into three categories.The most important is type II cells, which have nerve endings gathered near the bottom of the cells, and have more synaptic connections.The second is type I cell, which may be aSertoli cell。In the third kind of cells, there is often a mucilaginous substance in the taste pores with fewer taste buds, covering the microvilli of taste cells.When the ingredients in food are mainlyWater solubilityComponents can causecell membraneOpen the channel of an ion, so thatMembrane potentialFluctuation occurs, and the taste cells are excitedsynaptic transmission, causing excitation of afferent nerve endings.For example, H+and Na+can excite taste cells.Generally variouscationCan excite taste cells, andanionOfteninhibition, some of the cellsproteinMolecules can combine with certain parts of carbohydrate molecules, which may be the basis of sweet sense.Compounds with N-C=S group in the solution can cause bitter taste.
Olfactory receptor
The olfactory receptor, like the taste receptor, is more important to general animals than to humans, and the sense of smell is more important than the sense of taste, because the olfactory receptor can sense distant stimuli, can also sense the changes of substances in the environment within a certain time (up to several days), and can also act with the taste receptor at the same time to identify the characteristics of external substances.aquaticIts olfactory receptor can sense the gas components dissolved in water or staying on the water surface.Generally, substances that can excite olfactory receptors are mainly gases,volatilityOils, acids (such as HCI), and some substances can becomeSuspended solids, or suspended substances in steam (such as components in odor fog).Most of the substances that can excite the olfactory receptor must first dissolve in the mucus on the surface of the olfactory mucosa, or directly dissolve in theOlfactory cellMembranouslipidMedium.In the process of evolution, some animals have particularly developed olfactory receptors, and the area of olfactory mucosa is particularly large. For example, dogs and sharks are two outstanding examples.The human olfactory receptor is located in the upper part of the nasal cavity, and the area of the olfactory mucosa is not large.So the sense of smell is not very sensitive.Many advanced animals with underdeveloped sense of smell often use forced inhalation to make the air flow rush upwardNasal meatusTo smell the gas.
Smell is an important sense for people and animals to recognize the environment. Especially, social animals can often be used to identify enemies and friends, find nests, remember the way home, chase prey, escape harm, and find mates.In identifying food and exploring the synergistic activities of olfactory receptors and taste receptors in toxic substances.
lower animalFor example, the antennae of insects have olfactory receptors, and trace chemicals in the environment they fly or pass throughmaterialThey are very sensitive.Some female insects can secretePheromone(or called pheromone), which can lure male insects from a long distance.MarineScallop in ShellFor evading the enemy, such asStarfishAnd developed a very sensitive sense of smell.If a very small amount of starfish immersion solution is added to the sea water where it is, an escape reaction will occur immediately.In higher or lower animalsvertebrateBoth have extremely sensitive olfactory function.For example, sharks can smell people falling into the water several kilometers away.Dogs have a very good sense of smell and can be trained by humans to detect animals with high efficiency.The function of olfactory receptor is related to the sexual activity of some animals.goldenVoleWhen the female mouse is in estrus, it can emit a special smell, which can stimulate the male mouse after smelling itestrusPhysiological activities of.The human sense of smell can improve the ability of discrimination after training and learning, for example, doctors can diagnose certain diseases by sense of smell.
The structure of olfactory receptors in higher animals, including humans, is mainly concentrated in the upper and rear parts of the nasal cavity, calledOlfactory epithelium(olfactory mucosa).Human olfactory receptors are mainlySuperior turbinateandMiddle turbinateThe total area on both sides of the upper part is about 5 square centimeters.The olfactory epithelium contains three types of cells: ① olfactory cilia grow at the outer end of olfactory cells,SomaBottle shaped, round nucleus, long bottom of cellsaxon, it goes throughEthmoid boneget intoOlfactory bulb, namely, smellnerve fiberThe olfactory cilia of the cells extend to the mucosal surface, covered with a layer of mucus. ②Long columnSertoli cell。③Basal cellThe olfactory cells and supporting cells are parallel to each other and located above the basal cells.The membrane of olfactory cells is complex, and they can sense the connection of various substances and moleculesRecipient point(receiving point) may haveSpecificity。
Except human andMonkeyOutside, manymammalIn itsnasal septumThere is a cystic structure at the front end of the bottom, and the wall of the cyst is composed of cartilage and mucosa, calledVomeronasal apparatusIts mucosal structure is similar to that of olfactory epithelium.The vomeronasal organ cavity is connected with the oral cavity and nasal cavity by several thin tubescentral nervous systemIts connection is different from the common olfactory conduction pathway. It does not pass through the olfactory bulb, but through the accessory olfactory systemAccessory olfactory bulbAndCerebral cortexDirect contact, projected onto the brainPyriform leafSeptumandamygdala。This organ may be related to the emergency defense activities of animals.
SmellreceptorOfAfferent nerveIt is the axon of the olfactory cell. The olfactory cell itself is equivalent to the first level of other receptorsneuron。The second order neurons of olfactory impulse conduction pathway are in the olfactory bulb, which isthe forebrainThe front extension of the.
carotid arteryThe body is located at the bifurcation of the common carotid artery. It is about 3 × 1.5 × 1.5 mm in humans and only 1~2 mm long oval bodies in cats or dogs.The structure of the carotid body is special and consists of two kinds of cells: type I cells (also calledArterial bulbCell), the cell body is large, round, and contains moremitochondrion。There are many fine nerve endings around the cells.Type II cells are structurallySertoli cellorInterstitial cell, distributed around type I cells.CarotidAfferent nerve fiberJoin toCarotid sinusIn nerves, enteringMedulla oblongataOfNucleus tractus solitarius。There are many small cells in the carotid bodyBlood sinus, and directly from the external carotid arteryarterioleThe tubes are connected, so when the blood composition in the carotid artery changes, the blood in the carotid body will also change.
Carotid bodyChemoreceptor, which plays an important role in the regulation of respiratory movement, can sense C in bloodO2partial pressureIncrease, causing rapid breathing, so as to discharge too much CO2.When in the bloodO2 partial pressureWhen it is too low, the afferent impulse through this receptor can also reflexively strengthen the respiratory movement to obtain more O2.In addition, it is also harmful to some toxic drugs (such ascyanide）Sensitive and sensibleHazardous substancesStimulating function, which ultimately leads toDefensive reflexThe occurrence of.
These receptors are distributed inMuscularisorMucosal layerInternalFree nerve endings, when local inflammation occurs,Organizational decompositionPeptides produced orlactic acidSuch increase will stimulate these nerve endings and accelerate the release of their afferent impulses, which will be transmitted from visceral afferent nerve fibers to the central nervous system, causing severe pain.
kidneyParabulbar apparatusThe parabulbar organ cells of the kidney can sense Na+whenAfferent arterioleWhen the internal Na+concentration decreases, it can excite the parabulbar organ cells to releaserenin, results in bloodAngiotensin IIWhen the concentration ofadrenal cortex, make it secreteAldosterol, resulting inRenal tubuleThe reabsorption capacity of Na+is strengthened.central nervous systemIn the central nervous system, except for the nuclei and neurons of certain structureYesDifferenttransmitterIn addition to the receptive ability of peptides, some parts also have the function of receptors.For example, there is a large area in the ventrolateral part of the medulla oblongata that is very sensitive to changes in blood components, called the chemoreceptor area, which can sense the stimulation of elevated CO+partial pressure in the blood.In the anterior ventral area of the third ventricle, there is a receptor area for angiotensin II.stayhypothalamusStill feel the frontBlood glucoseSensors of concentration change, etc.
