Chemical_Senses

Chemical_Senses - Chemosensory Systems Chemosensory Systems...

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Chemosensory Systems
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Chemosensory Systems • Although the body can detect chemicals internally (changes in oxygen or carbon dioxide, for e.g.), we will focus on chemicals detected by the tongue and in the nose. • Flavor = Perception of olfaction (smell) + gustation (taste)
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Gustation (Taste) • Taste is the stimulation of receptor cells in taste buds. • Taste buds are receptive organs found on the tongue and parts of the throat. • Taste buds are found mostly on folds of skin called papillae : 1. Fungiform 2. Vallate (Circumvallate) 3. Foliate 4. Filiform (no taste buds on these)
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Taste Buds • Taste buds consist of 50-100 cells. • Each taste bud has capsule cells which form an outer protective layer. • At the surface, there is a taste pore , through which tastants (chemicals that can be tasted) enter. • Within each taste bud, there are sensory receptor cells and basal, stem cells. • The basal, stem cells give rise to new receptor cells.
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Taste Buds • Sensory, receptor cells have microvilli at their surface to increase surface area for detecting tastants. • Taste transduction occurs in the microvilli. • Taste receptor cells are not neurons (they are specialized epithelial cells) innervated by cranial nerves. • If taste buds lose innervation, they disappear but can regenerate with new innervation and stem cell differentiation.
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Taste Bud Innervation • The tongue is innervated by cranial nerves VII, IX, and X: 1. The facial nerve (cranial nerve VII, chorda tympani is one branch of facial nerve) innervates the anterior tongue. 2. The glossopharyngeal nerve (cranial nerve IX) innervates the posterior tongue. 3. The vagus nerve (cranial nerve X) innervates the epiglottis. • Approximately, 50 fibers innervate each taste bud.
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Sensory System Theories • Labelled Line Theory : Each receptor responds to a limited range of stimuli with a direct line to the brain. • Across-Fiber Pattern Theory : Each receptor responds to a range of stimuli and contributes to the perception of each of them. • Most sensory systems appear to use across- fiber patterns for encoding information. • The meaning of a response by a particular receptor depends on the context of responses by other receptors.
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• There are 5 taste qualities: 1. Sweet (sugars) 2. Sour (acids) 3. Salty (salts) 4. Bitter (Quinine) 5. Umani (taste of some amino acids and
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This note was uploaded on 04/24/2008 for the course BCS 110 taught by Professor Holtzman during the Spring '08 term at Rochester.

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Chemical_Senses - Chemosensory Systems Chemosensory Systems...

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