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Chapter 16 The Special Senses Smell and Taste Gustation • Taste receptors • Clustered in taste buds • Associated with lingual papillae LaPointe Fall ’11 Slide # 2 Taste buds in lingual papilla LaPointe Fall ’11 Slide # 3 • Fungiform • small, ~5 taste buds • most numerous • tongue and throughout oral cavity • Foliate • Leaf-shaped. In folds on the sides of the tongue. • Contain most sensitive taste buds. Decrease in number with age. • Vallate (circumvallate) - large, ~100 taste buds form V shape pattern Filiform papillae • Filiform papillae • most numerous papillae • do not contain taste buds • give tongue rough surface LaPointe Fall ’11 Slide # 4 Taste buds LaPointe Fall ’11 Slide # 5 • Contain basal cells which appear to be stem cells • Gustatory cells (epithelial cells) extend specialized microvilli (taste hairs) through a narrow taste pore Gustatory Reception (also see Saladin fig 16.6) LaPointe Fall ’11 Slide # 6 Figure 15.23 Gustatory discrimination LaPointe Fall ’11 Slide # 7 • Primary taste sensations • Sweet, sour, salty, bitter, umani • Receptors also exist for umami (amino acids) and water? • Bitter> acid>> salt or sweet • Taste sensitivity shows significant individual differences, some of which are inherited e.g. phenylthiourea • Interaction with smell Taste receptor activation salt acid LaPointe Fall ’11 Slide # 8 sweet, bitter, umami Gustatory pathways LaPointe Fall ’11 Slide # 9 • Taste buds are monitored by cranial nerves VII, IX, X (first order neurons) • Synapse within the solitary nucleus of the medulla oblongata (second order neurons) • Then on to the thalamus via the medial lemniscus pathway and the primary sensory cortex • Parallel pathways go to the hypothlamus and other brain regions and activate reflex responses (salivation, stomach churning, etc) Olfactory organs LaPointe Fall ’11 Slide # 10 • Olfactory epithelium • Olfactory receptor cells • are modified bipolar neurons • contain specialized cilia (olfactory hairs) • Olfactory receptor cell population shows considerable turnover • Each cell only has one type of receptor (binds only one type of odorant) • basal cells • supporting cells, • Surfaces are coated with secretions from olfactory glands Olfaction LaPointe Fall ’11 Slide # 11 • Olfactory reception involves detecting dissolved chemicals as they interact with odorant binding proteins • Can distinguish >10,000 of chemical stimuli • Thousands of receptors in most mammals!!!! Humans appear to have only ~350 different receptors • CNS interprets smells by pattern of receptor activity • Little receptor adaptation, but central adaptation occurs • Granule cells can inhibit signals going to the olfactory centers Olfactory pathways LaPointe Fall ’11 Slide # 12 • Do not synapse in the thalamus first (although some collateral axons go to the thalamus) • Olfactory bulbs are extensions of the cerebrum • mitral cells and tufted cells synapse with bipolar cells in glomeruli • each glomerulus receives one type of signal • Olfactory tracts mainly go first to the temporal lobe (primary olfactory center) • Collaterals go to the limbic system • Frontal lobe allows the discrimination of different odors and integrates smell and taste The Olfactory Organs LaPointe Fall ’11 Slide # 13 Receptor activation LaPointe Fall ’11 Slide # 14 Figure 15.22