Unit Ten: The Nervous System: B. Special Senses

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Unit Ten The Nervous System B. Special Senses

• Chapter 53 The Chemical SensesTaste and Smell

Guyton and Hall, Textbook of Medical Physiology,
12th edition
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Sense of Taste

• Primary Sensation of Taste
• Sour
• Salty
• Sweet
• Bitter
• Umami

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Sense of Taste

• Threshold for Taste- much more sensitive to
  bitter
• taste than all of the others (important
• protective function from toxins in food)
• Taste Blindness- some people are taste blind
  for
• substances phynylthiocarbamide (15-30 of
• people) unknown reasons

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Sense of Taste

• Taste Buds and Their Function

Fig. 53.1 Taste bud
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Sense of Taste

• Taste Bud Location- found on three types of
• papillae on the tongue
• Large number on the walls of the troughs that
• surround the circumvallate papillae
• Moderate numbers on the fungiform papillae over
• the flat anterior surface of the tongue
• Moderate numbers on the foliate papillae on the
• folds along the lateral surface of the tongue
• Also on palate, tonsils, epiglottis, and proximal
• esophagus
• e. Adults have 3000-10000 degenerate with age
  (45 yrs)

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Sense of Taste

• Specificity of Taste Buds- each taste bud
  responds
• mostly to one of the five primary taste stimuli
• when the substance is in low concentration high
• concentrations will stimulate two or more taste
  bud
• types

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Sense of Taste

• Mechanism of Stimulation
• Receptor potential- substance causes the taste
  hair
• to depolarize
• For salty and sour, the receptor opens specific
  ion
• channels
• For sweet and bitter, a second messenger is
• activated
• b. Generation of nerve impulses by the taste bud

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Sense of Taste

• Transmission of Taste Signals into the CNS

Fig. 53.2
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Sense of Taste

• Rapid Adaptation of Taste
• Taste Preference- results from a mechanism
  within
• the CNS can develop taste aversion or negative
• taste preference

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Sense of Smell

• Olfactory Membrane

Fig. 53.3
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Sense of Smell

• Olfactory Cells
• bipolar nerve cells 100 million interspersed
• between the sustentacular cells
• Olfactory hairs project into the mucus that
• coats the inner surface of the nasal cavity
• Hairs form a dense mat in the mucus, react to
• odors, and stimulate the olfactory cells
• Bowemans glands secrete mucus onto the surface
• of the membrane

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Sense of Smell

• Stimulation of the Olfactory Cells
• Odorant substance binds to receptor proteins in
• the membrane of each cilium (hair cell)
• Receptor proteins folds its way into and out of
  the
• membrane about 7 times
• Inside fold is bound to a G protein which then
• activates adenyl cyclase to form cAMP
• d. cAMP activates gated sodium ion channels to
  open

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Sense of Smell

• Stimulation of the Olfactory Cells
• Ions pour in and depolarize the membrane
• Excites the olfactory nerve and transmits Aps
• into the CNS
• Only volatile substances can be smelled
• Substances must be soluble in water
• Helpful to be slightly lipid soluble

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Sense of Smell

• Rapid Adaptation of Olfactory Sensations- 50
• in the first couple of seconds
• Primary Sensations of Smell
• Camphoraceous
• Musky
• Floral
• Pepperminty
• Ethereal
• Pungent
• Putrid

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Sense of Smell

• Transmission of Smell Signals into the CNS

Fig. 53.5 Neural connections of the olfactory
system