November 12 - Taste & Olfaction.docx

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Anatomy and Cell Biology
Anatomy and Cell Biology 3319

November 12, 2013 Taste & Olfaction Pg. 483-486 The Chemical Senses: Taste and Smell - The receptors for taste (gustation) and smell (olfaction) are classified as chemoreceptors because they respond to chemical substances Taste (Gustation) - Taste buds - taste receptors occur in taste buds in the mucosa of the mouth and pharynx - About 10,000 taste buds on surface of tongue - A few taste buds occur on the posterior region of the palate (roof of mouth), on the inner surface of the cheeks, on the posterior wall of the pharynx, and on the epiglottis - Most taste buds occur in peglike projections of the tongue mucosa called papillae o Taste buds occur within the epithelium that covers the papillae - In the small fungiform papillae scattered over the entire surface of the tongue, the taste buds are on the apical surface - In the large vallate papillae arranged in an inverted V near the back of the tongue, the taste buds are in the side walls - Each taste bud is a globular collection of 50-100 epithelial cells that resemble a bud on a tree - Each contains 2 major cell types: o Gustatory epithelial cells  Long microvilli called gustatory hairs project from the gustatory epithelial cells and extend through a taste pore to the surface of the epithelium  These microvilli are bathed in saliva containing the dissolved molecules that stimulate taste  These molecules bind to the plasma membrane of the microvilli to generate impulses in the sensory nerve fibers that innervate them o Basal epithelial cells - The cells in taste buds are replenished every 7-10 days by the division of the basal epithelium cells, replacing the gustatory epithelial cells that are scraped and burned off during eating - If an entire taste bud is destroyed, a new one will form after its nerve ending grows back into the regenerating epithelium Taste Sensations and the Gustatory Pathway - 5 basic qualities of taste: o Sweet, sour, salty, bitter, and umami (Japanese for “deliciousness”)  Umami is elicited by a substance called glutamate that is found naturally in meat, aged cheeses, and tomatoes  All modalities of taste can be elicited from all areas that contain taste buds - Taste info. reaches the brain stem and cerebral cortex through the gustatory pathway o Sensory fibers carrying taste info. from the tongue occur primarily in 2 cranial nerves:  CN7 – facial nerve – transmits impulses from taste receptors in the anterior 2/3 of the tongue  CN9 – glossopharyngeal nerve – carries sensations from the tongues posterior third, as well as from the few taste buds in the pharynx o Additional taste impulses from the few taste buds on the epiglottis and lower pharynx are conducted by the vagus nerve (CN10) o All these sensory neurons that carry taste info. synapse in a nucleus in the medulla called the solitary nucleus o From there, impulses are transmitted to the thalamus and ultimately to the gustatory area of the cerebral cortex in the insula lobe Smell (Olfaction) - Receptors for smell lie in a patch of epithelium on the roof of the nasal cavity - Receptors are part of the olfactory epithelium that
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