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Special Senses Outline

Special Senses Outline - Chapter 17 The Special Senses I An...

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Chapter 17: The Special Senses I. An Introduction to the Special Senses, p. 550 The five special senses are: olfaction , gustation , vision , equilibrium , and hearing . II. Olfaction, p. 550 The olfactory organs are located in the nasal cavity on either side of the nasal septum. The olfactory epithelium contains the olfactory receptors , supporting cells, and basal (stem) cells . The lamina propria consists of areolar tissue, numerous blood vessels, nerves, and olfactory glands. The surfaces of the olfactory organs are coated with the secretions of the olfactory glands . Olfactory Receptors, p. 551 The olfactory receptors are highly modified neurons. Olfactory reception involves detecting dissolved chemicals as they interact with odorant-binding proteins. Olfactory Pathways , p. 551 Axons leaving the olfactory epithelium collect into 20 or more bundles that penetrate the cribriform plate of the ethmoid bone to reach the olfactory bulbs of the cerebrum where the first synapse occurs. Axons leaving the olfactory bulb travel along the olfactory tract to reach the olfactory cortex, the hypothalamus, and portions of the limbic system. In olfaction, the arriving information reaches the information centers without first synapsing in the thalamus. Olfactory Discrimination, p. 551 The olfactory system can distinguish thousands of chemical stimuli. The CNS interprets smells by the pattern of receptor activity. Aging and Olfactory Sensitivity, p. 551 The olfactory receptor population shows considerable turnover. The number of olfactory receptors declines with age. III. Gustation, p. 552 Taste (gustatory) receptors are clustered in taste buds . The human tongue has three types of lingual papillae: 1. filiform papillae : provide friction, do not contain taste buds 2. fungiform papillae : contains five taste buds each 3. circumvallate papillae : contain as many as 100 taste buds each Taste Receptors, p. 553 Each taste bud contains basal cells , which appear to be stem cells, and gustatory cells , which extend taste hairs through a narrow taste pore . A typical gustatory cell survives for only about 10 days before it is replaced. Gustatory Pathways, p. 553 The taste buds are monitored by cranial nerves that synapse within the solitary nucleus of the medulla oblongata and then on to the thalamus and the primary sensory cortex. Gustatory Discrimination, p. 553 The primary taste sensations are sweet, salty, sour, and bitter. Humans have two additional taste sensations: 1. umami : characteristic of beef and chicken broths and parmesan cheese. Detected by receptors sensitive to amino acids, small peptides, and nucleotides. 2. water: detected by water receptors in the pharynx. Dissolved chemicals contacting the taste hairs bind to receptor proteins of the gustatory cell. Different tastes involve different receptor mechanisms.
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