what are the cells that make up the sensory organ

1 ANSWERS

1. amomipais82
   

   HI,
   Taste
   Taste buds are the sensory receptor organs for taste. Each taste bud is composed of 40 to 100 epithelial cells of three different types: supporting cells, receptor, or taste cells and basal cells. These actually represent three developmental stages of the same cell line. Basal cells act as stem cells, dividing and differentiating into supporting cells, which then, in turn differentiate into mature taste cells.
   
   Supporting cells occupy most of the taste bud. They function to insulate the mature taste cells from each other and from the surrounding tongue epithelium. Both they and the mature taste cells possess long microvilli called gustatory hairs, which project through a taste pore to the surface epithelium. These hairs are believed to be the receptor portions of the taste cells. Sensory dendrites are coiled around the taste cells, representing the initial part of the gustatory pathway to the brain.
   
   Smell
   The organ of smell is the olfactory epithelium. This pseudostratified layer is composed of olfactory receptor cells, supporting cells, and basal cells.
   
   Olfactory cells are bipolar nerve cells characterised by the olfactory vesicle, from which several olfactory cilia extend. These long, nonmotile cilia act as the receptors for smell. Olfactory cells are surrounded and cushioned by supporting cells, and they are renewed by the dividing and differentiating basal cells.
   
   Bowman’s glands are located in the connective tissue of the lamina propria beneath the olfactory epithelium. They secrete a mucous which is released onto the olfactory epithelial surface via ducts. This fluid acts as a solvent in which odorous molecules dissolve, and are then detected by the olfactory cell receptors. The secretion is continually renewed, ensuring that old odours are flushed away, leaving the receptors free to detect new stimuli.
   
   Sight
   The retina of the eye is responsible for photo reception. Its inner, neural layer is principally composed of three cell types: photoreceptors, bipolar neurons and ganglion cells. There are two types of photoreceptors, rods and cones. Rods are sensitive to light of low intensity, while cones are sensitive to high intensity light. Muller cells function as the supporting elements of the retina. They are highly columnar cells which extend from the inner surface of the retina to the inner segments of the photoreceptors.
   
   The outer layer of the retina is composed of pigmented epithelial cells, which play a role in light absorption, as well as in the synthesis of vitamin A and phagocytosis. Within the tunic vasculosa of the eye, there are also layers of pigmented epithelial cells, and also nonpigmented, columnar epithelium.
   
   A layer of cuboidal epithelial cells underlies the capsule of the lens on the anterior surface. Towards the middle of the lens, the cells become elongated in a process of differentiating into lens fibres.
   
   The lacrimal gland is one of the eye’s accessory structures. It is a compound tubuloalveolar gland which secretes tears which serve to moisten and lubricate the cornea and conjunctiva. Tears contain the antibacterial enzyme lysozyme, and therefore they also protect the eye against bacterial infections.
   
   Sound
   The hair cells of the organ of Corti within the inner ear are divided into two types: inner and outer hair cells. The outer hair cells, illustrated below, are columnar, with a basal nucleus and a specialised receptor surface. Inner hair cells are similar, but are goblet shaped. Each cell has over 100 sensory, stiff stereocilia, which are arranged in parallel rows on the apical surface, and are in contact with the tectorial membrane. Sound wave induced vibrations of the basilar membrane cause the hair cells to move laterally, and shear their stereocilia against the tectorial membrane. Movement of the stereocilia causes depolarisation of the hair cell, which is then transduced to the brain via the cochlear nerve, fibres of which are coiled around the basal membrane of the hair cells.
   
   Together with the hair cells, there are several different types of supporting cell in the organ of Corti, including inner and outer pillar cells, inner and outer phalangeal cells, cells of Hensen, and border cells. These supporting cells share many characteristics, and differ primarily in their shape and position relative to other cells.
   
   Covering the outer wall of the cochlear duct is the stria vascularis, a thick vascularised epithelium, which secretes endolymph, and which is composed of three cell types: marginal, intermediate and basal cells.
   
   The sensory cells within the vestibular labyrinth are type I and type II hair cells. Type I cells are bulbar in shape and a re almost completely surrounded by a cup-shaped afferent nerve endings. Type II cells are columnar in shape and they make contact with small afferent nerve terminals containing synaptic vesicles. Both cell types possess 50-100 elongated, rigid stereocilia (microvilli) arranged in rows and a single kinocilium (a true cilium) arranged along their apical surface, and embedded in the otolithic membrane above. They function to detect changes in the position of the head. Supporting cells surround the hair cells and make up the majority of the cell population.
   
   Cristae ampullares are specialised sensory regions within the ampullae of the semicircular ducts. They have a high density of mitochondria which is indicative of a high metabolic rate, and together with the presence of secretory vesicles, they suggest that the dark cells of the crista ampullaris may synthesise and secrete endolymph.
   
   The endolymph sac is the expanded end of the endolymphatic duct within the vestibular labyrinth. It has an epithelial lining containing light cells, with microvilli extending from their apical surface and many cytosolic vesicles, and electron-dense dark cells with abundant cytoplasmic filaments running between the organelles. The light cells are thought to play a role in the reabsorption of endolymph, while the dark cells have been shown to phagocytose particles within the endolymphatic sac and are believed to be a defensive mechanism within the inner ear.

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