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	{{Arey1924 Header}}		{{Arey1924 Header}}

	~~CHAPTER~~ XV ~~THE SENSE ORGANS~~		=Chapter XV The Sense Organs=


	The sense cells of primitive animals, such as worms, are ectodermal in origin and position. Only those of the vertebrate olfactory organ have retained this primitive positional relation, although the germ-layer origin is unchanged. During ]jhylogenesis the cell-bodies of all other such primary sensory neurones, except smell, migrated inward to form the dorsal ganglion (Parker), hence their peripheral processes either end freely in the epithelium, are associated with various sensory corpuscles, or appropriate new cells to serve as sensory receiptors (taste; hearing).		The sense cells of primitive animals, such as worms, are ectodermal in origin and position. Only those of the vertebrate olfactory organ have retained this primitive positional relation, although the germ-layer origin is unchanged. During ]jhylogenesis the cell-bodies of all other such primary sensory neurones, except smell, migrated inward to form the dorsal ganglion (Parker), hence their peripheral processes either end freely in the epithelium, are associated with various sensory corpuscles, or appropriate new cells to serve as sensory receiptors (taste; hearing).
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	Among the sense organs are receptive elements of general sensibility which Ipelong to the integument, muscles, tendons, and viscera; these mediate such sensations as touch, pressure, muscle and tendon sensibility, temperature, and pain. Other organs, of a special sensory nature, are responsible for the sensations of taste, smell, vision, and hearing. Each is tuned to a specific and exclusive kind of stimulus. The organs of smell, vision, and hearing are distance receptors, in contrast to all others which collect information from the organism itself and especially from its integument. The apparatus for smell and taste consists of little more than the ' special sensory cells alone, whereas the eye and ear possess elaborate accessory mechanisms for receiving the external stimulus and converting it into a form suitable to affect the sensory cells proper.		Among the sense organs are receptive elements of general sensibility which Ipelong to the integument, muscles, tendons, and viscera; these mediate such sensations as touch, pressure, muscle and tendon sensibility, temperature, and pain. Other organs, of a special sensory nature, are responsible for the sensations of taste, smell, vision, and hearing. Each is tuned to a specific and exclusive kind of stimulus. The organs of smell, vision, and hearing are distance receptors, in contrast to all others which collect information from the organism itself and especially from its integument. The apparatus for smell and taste consists of little more than the ' special sensory cells alone, whereas the eye and ear possess elaborate accessory mechanisms for receiving the external stimulus and converting it into a form suitable to affect the sensory cells proper.

			==General Sensory Organs==


	~~GENERAL SENSORY ORGANS~~

	Free nerve terminations form the great majority of all the general sensory organs. When no sensory corpuscle is developed, the neurofibrils of the sensory nerve fibers separate and end among the cells of the epithelia.		Free nerve terminations form the great majority of all the general sensory organs. When no sensory corpuscle is developed, the neurofibrils of the sensory nerve fibers separate and end among the cells of the epithelia.
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	~~THE GUSTATORY ORGAN~~		==The Gustatory Organ==

	In fetuses of three months, thickenings of the lingual epithelium represent the future taste buds. The parent tissue is quite clearly entoderm, yet an ectodermal origin is sometimes asserted. The cells of an anlage lengthen and extend to the surface of the epithelium. The ovoid mass then differentiates into sensory taste cells, with modified cuticular tips, and into supporting cells. Taste buds are supplied by nerve fibers of the seventh, ninth, and tenth cranial nerves; the fibers branch and end in contact with the periphery of the taste cells.		In fetuses of three months, thickenings of the lingual epithelium represent the future taste buds. The parent tissue is quite clearly entoderm, yet an ectodermal origin is sometimes asserted. The cells of an anlage lengthen and extend to the surface of the epithelium. The ovoid mass then differentiates into sensory taste cells, with modified cuticular tips, and into supporting cells. Taste buds are supplied by nerve fibers of the seventh, ninth, and tenth cranial nerves; the fibers branch and end in contact with the periphery of the taste cells.

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Book - Developmental Anatomy 1924-15 - Revision history

Z8600021 at 06:34, 24 October 2016

Z8600021 at 23:11, 22 October 2016

Z8600021 at 02:29, 22 October 2016

Z8600021: Created page with "{{Arey1924 Header}} CHAPTER XV THE SENSE ORGANS The sense cells of primitive animals, such as worms, are ectodermal in origin and position. Only those of the vertebrate olf..."