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Similarly, within the vestibular labyrinth see Highstein et al. The greater density of these otoliths imparts a similar shearing force onto the ciliary bundles whenever the head alters its position with respect to gravity or experiences acceleration. In the semicircular canals the hair bundles of the sensory epithelium extend into a compliant gelatinous cupula that occludes the canal.
Thus, movements of the endolymphatic fluids deflect the cupula in response to angular acceleration of the head. An equivalent system is found in the lateral line of fish and some amphibians, a fluid-filled skin canal with numerous pores opening to the outside. Here, neuromasts lining the canals of the trunk and head feature ciliary tufts embedded in a gelatinous cupula that extends into the canal.
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Fluid movements inside the canals deflect the cupula as a result of pressure differences alongside the fish. Additional, superficial neuromasts are scattered over the skin surface of fish and amphibians, as illustrated in a superficial neuromast of the bristlenose catfish, Ancistrus Figure 2 , M. Hofmann, unpublished; k, kinocilia; s, stereocilia. Hair cell morphology highlights a conservative evolutionary feature of cell biology as it relates to sensory systems.
For example, vertebrate rods and cones arise during development as extensions of a ciliary membrane whose invaginations and vesicles form the outer segments containing photopigments. Olfactory cells also feature cilia, the membranes of which contain the odorant binding receptors and G-proteins that initiate sensory transduction.
Likewise, modified ciliary structures are characteristic of many primary mechanosensory neurons where dendrites contain the 9 pairs of ciliary fibrils extending from a ciliary base. Indeed, the cilium arose early on in eukaryotic organisms as a cellular compartment for sensing the environment, as in ciliate protozoans where it functions simultaneously as a sensory antenna and locomotory organelle.
For example, a mechanical stimulus applied to the anterior cilia of Paramecium triggers a spike-like membrane potential and calcium current that reverses the effective stroke of ciliary beating resulting in reversed swimming. Cilia aside, mechanoreception is poorly understood in invertebrate animals, with the notable exception of arthropods.
Rather, branching free nerve endings in the epithelial tissues, about which little is known other than their morphological description, appear to mediate tactile responses. Various invertebrates feature a sensory epithelium that extends into bristles or papillae that function as sensory hairs. Statocysts, invaginations lined with sensory hairs deflected by a statolith, are recognizable in animals as diverse as jellyfish, mollusks, and a few worms and echinoderms, but corresponding physiological analyses are largely unavailable.
Exceptions include the body wall stretch receptors of annelid worms, the tactile sense organs richly endowed in cephalopod suckers, and arthropods.
Nevertheless, fruit fly Drosophila and soil nematode C. The study of arthropod mechanoreceptors rivals that of vertebrates and the diversity of internal and external receptors is enormous. Like vertebrates, arthropods feature a rigid exo skeleton, which also serves as the external integument. With a relatively non compliant exterior surface devoid of epithelium and undifferentiated free nerve endings, crustaceans, insects, spiders and their allies feature a wide variety of receptors specialized to detect both the outside world as well as body structures internally.
Many are analogous to those of the skeletonized vertebrates, e. Here, stretch sensitive sensory cells are embedded within strands of muscle or elastic elements that span the joints of body and appendage segments.
The muscle receptor organ MRO of crayfish and lobster is a clear analog of the vertebrate muscle spindle organ. Here, the dendrites of two sensory neurons, one phasic and one tonic, are embedded within muscle strands stretched as the abdomen flexes.
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Sensitivity is modulated by efferent feedback to the muscle fibers that adjusts length and tension in the muscle over a range of postures. As in vertebrates, arthropod mechanoreceptors underlie the function of multiple sensory modalities, including the tactile senses, audition, and sensitivity to gravity. The scolopidial organ is a common element of many of these systems and the site of sensory transduction where one or more bipolar receptor cells with a ciliary distal process are ensheathed and capped by various cuticular end organs.
For example, the chordotonal organs are scolopidia embedded in connective tissue attached to and stretched by joint movements.
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Campaniform organs, oval patches of flexible cuticle, cap receptors that monitor cuticular stress. Often located in the leg bases, these receptors detect loading relative to orientation and gravity.
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Ta kontakt med Kundesenteret. Avbryt Send e-post. Les mer. Om boka Evolution of the Vertebrate Auditory System The function of vertebrate hearing is served by a surprising variety of sensory structures in the different groups of fish, amphibians, reptiles, birds, and mammals.
Toggle navigation Home. Contact Copyright Privacy. Home Vertebrate Hair Cells: 27 Springer Book file PDF easily for everyone and every device. This Book have some digital formats such us :paperbook, ebook, kindle, epub, fb2 and another formats. Evolution of the Vertebrate Auditory System SpringerLink A stepwise series of parallel stereocilia, increasing in length until they meet a single, longer kinocilium, form an intricate, polarized transducing system. Vertebrate Hair Cells?
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