Transcript Special senses

Chemical Senses
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Chemical senses – gustation (taste) and olfaction
(smell)
Their chemoreceptors respond to chemicals in
aqueous solution
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Taste – to substances dissolved in saliva
Smell – to substances dissolved in fluids of the
nasal membranes
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Sense of Smell
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The organ of smell is the olfactory epithelium, which covers the
superior nasal concha
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Olfactory mucosa contains 10–20 million olfactory cells
(bipolar neuron), each of which bears 10–20 cilia called
olfactory hairs.
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Olfactory receptor cells are bipolar neurons with radiating
olfactory cilia
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Olfactory receptors are surrounded and cushioned by supporting
cells
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Basal cells lie at the base of the epithelium
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Olfactory Receptors
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Figure 15.21
Physiology of Smell
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Olfactory receptors respond to several different
odor-causing chemicals
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When bound to ligand these proteins initiate a
G protein mechanism, which uses cAMP as a
second messenger
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cAMP opens Na+ and Ca2+ channels, causing
depolarization of the receptor membrane that then
triggers an action potential
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Taste Buds
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Most of the 10,000 or so taste buds are found on
the tongue
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Taste buds are found in papillae of the tongue
mucosa
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Papillae come in three types: filiform, fungiform,
and circumvallate
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Fungiform and circumvallate papillae contain taste
buds
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Taste Buds
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Figure 15.23
Taste Sensations
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There are five basic taste sensations
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Sweet – sugars, saccharin, alcohol, and some
amino acids
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Salt – metal ions
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Sour – hydrogen ions
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Bitter – alkaloids such as quinine and nicotine
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Umami – elicited by the amino acid glutamate
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Physiology of Taste
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In order to be tasted, a chemical:
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Must be dissolved in saliva
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Must contact gustatory hairs
Binding of the food chemical:
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Depolarizes the taste cell membrane, releasing
neurotransmitter
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Initiates a generator potential that elicits an action
potential
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General sensations
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General senses (also called somatic, somatosensory,
or somesthetic) have receptors that are widely
distributed throughout the body.
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These detect touch, pressure, heat, cold, and pain, as
well as many other stimuli that we do not consciously
perceive.
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The special senses are limited to the head, including
vision, hearing, equilibrium, taste, and smell.
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Functional classification of Receptors
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Chemoreceptors respond to chemicals.
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Thermoreceptors respond to temperature
changes.
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Nociceptors are pain receptors and sense tissue
damage.
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Mechanoreceptors respond to a physical change
in their shape.
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Photoreceptors respond to light.
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Receptors can be classified according to the origins of their
stimuli:
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Interoceptors detect stimuli from internal organs.
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Proprioceptors sense position and movement of
the body or its parts.
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Exteroceptors detect external changes
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Exteroceptors
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Respond to stimuli arising outside the body
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Found near the body surface
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Sensitive to touch, pressure, pain, and temperature
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Include the special sense organs
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Interoceptors
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Respond to stimuli arising within the body
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Found in internal viscera and blood vessels
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Sensitive to chemical changes, stretch, and
temperature changes
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