Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Senses Chemical senses – gustation (taste) and olfaction (smell) Their chemoreceptors respond to chemicals in aqueous solution Taste – to substances dissolved in saliva Smell – to substances dissolved in fluids of the nasal membranes
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sense of Smell The organ of smell is the olfactory epithelium, which covers the superior nasal concha Olfactory mucosa contains 10–20 million olfactory cells (bipolar neuron), each of which bears 10–20 cilia called olfactory hairs. Olfactory receptor cells are bipolar neurons with radiating olfactory cilia Olfactory receptors are surrounded and cushioned by supporting cells Basal cells lie at the base of the epithelium
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Olfactory Receptors Figure 15.21
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Physiology of Smell Olfactory receptors respond to several different odor-causing chemicals When bound to ligand these proteins initiate a G protein mechanism, which uses cAMP as a second messenger cAMP opens Na + and Ca 2+ channels, causing depolarization of the receptor membrane that then triggers an action potential
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Taste Buds Most of the 10,000 or so taste buds are found on the tongue Taste buds are found in papillae of the tongue mucosa Papillae come in three types: filiform, fungiform, and circumvallate Fungiform and circumvallate papillae contain taste buds
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Taste Buds Figure 15.23
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Taste Sensations There are five basic taste sensations Sweet – sugars, saccharin, alcohol, and some amino acids Salt – metal ions Sour – hydrogen ions Bitter – alkaloids such as quinine and nicotine Umami – elicited by the amino acid glutamate
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Physiology of Taste In order to be tasted, a chemical: Must be dissolved in saliva Must contact gustatory hairs Binding of the food chemical: Depolarizes the taste cell membrane, releasing neurotransmitter Initiates a generator potential that elicits an action potential
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings General sensations
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings General senses (also called somatic, somatosensory, or somesthetic) have receptors that are widely distributed throughout the body. These detect touch, pressure, heat, cold, and pain, as well as many other stimuli that we do not consciously perceive. The special senses are limited to the head, including vision, hearing, equilibrium, taste, and smell.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Functional classification of Receptors Chemoreceptors respond to chemicals. Thermoreceptors respond to temperature changes. Nociceptors are pain receptors and sense tissue damage. Mechanoreceptors respond to a physical change in their shape. Photoreceptors respond to light.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Receptors can be classified according to the origins of their stimuli: Interoceptors detect stimuli from internal organs. Proprioceptors sense position and movement of the body or its parts. Exteroceptors detect external changes
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Exteroceptors Respond to stimuli arising outside the body Found near the body surface Sensitive to touch, pressure, pain, and temperature Include the special sense organs
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Interoceptors Respond to stimuli arising within the body Found in internal viscera and blood vessels Sensitive to chemical changes, stretch, and temperature changes