Chap17_2401 - 1 THE SPECIAL SENSES Chapter 17 Anatomy and...

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1 THE SPECIAL SENSES Chapter 17 Anatomy and Physiology Lecture
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2 THE SPECIAL SENSES (Special Senses - smell , taste , sight , hearing , and equilibrium - have receptor organs that are structurally more complex than receptors for general sensations.) Olfactory sensation - Smell Gustatory sensation - Taste Visual sensation - Sight Auditory and Equilibrium sensation - Hearing and balance *The sense of smell is the least specialized. *The sense of sight is the most specialized. OLFACTION Olfaction – The sense of smell, occurs in response to odors that stimulate sensory receptors located in the extreme superior region of the nasal cavity, called Olfactory recess . Olfactory Epithelium – Is the specialized nasal epithelium of the olfactory recess. Olfactory Epithelium and Bulb Ten Million olfactory neurons are present within the olfactory epithelium. Three Principal Kinds of Olfactory Epithelium Cells 1. Supporting (Sustentacular) Cells - Are columnar epithelial cells of the mucous membrane lining the nose.
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3 2. Olfactory Neurons - Are bipolar neurons whose cell bodies lie between the supporting cells. -The distal (free) end of each olfactory cell contains a dendrite that terminates in a swelling (olfactory vesicle) from which six to eight cilia, called olfactory hairs radiate. Hairs are believed to react to odors in the air and then to stimulate the olfactory cells, thus initiating the olfactory response. 3. Basal Cells - Lie between the bases of the supporting cells and are believed to produce new supporting cells. -Produce mucus , which is carried to the surface of the epithelium by ducts. -The secretion moistens the surface of the olfactory epithelium and serve as a solvent for odoriferous substances . -The continuous secretion of mucus also serves to freshen the surface film of fluid and prevents continuous stimulation of olfactory hairs by the same odor. Physiology of Olfactory In order for a substance to be smelled, it must be: 1. Volatile - capable of entering into a gaseous state so that the gaseous particles can enter the nostrils. 2. Water-soluble - that it can dissolve in the mucus to make contact with olfactory cells. 3. Lipid-soluble - Plasma membrane of olfactory hairs are largely lipid, the substance to be smelled must be dissolved in the lipid covering to make contact with olfactory hairs.
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4 Neuronal Pathway of Olfaction Olfactory Neurons (Cranial Nerve I) – Their axon enter the olfactory bulb, where they synapse with Mitral cells or Tufted cells . Mitral and Tufted cells relay olfactory information to the brain through the olfactory tracts and synapse with Association neurons in the Olfactory bulbs . -They pass through foramina in the Cribriform plate of the Ethmoid bone. Olfactory bulbs
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This note was uploaded on 03/10/2012 for the course BIOL 2403 taught by Professor Campbell during the Spring '12 term at Texas Pan American.

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Chap17_2401 - 1 THE SPECIAL SENSES Chapter 17 Anatomy and...

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