1. Unit Ten: The Nervous System: B. Special Senses
Chapter 53: The Chemical Senses—Taste and Smell
Guyton and Hall, Textbook of Medical Physiology, 12th edition

2. Sense of Taste
Primary Sensation of Taste
Sour
Salty
Sweet
Bitter
Umami

3. 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

4. Taste Buds and Their Function
Sense of Taste
Taste Buds and Their Function
Fig Taste bud

5. 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 ; degenerate with age (45 yrs)

6. 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

7. 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

8. Transmission of Taste Signals into the CNS
Sense of Taste
Transmission of Taste Signals into the CNS
Fig. 53.2

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

10. Sense of Smell
Olfactory Membrane
Fig. 53.3

11. 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
Boweman’s glands secrete mucus onto the surface
of the membrane

12. 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

13. 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

14. 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

15. Transmission of Smell Signals into the CNS
Sense of Smell
Transmission of Smell Signals into the CNS
Fig Neural connections of the olfactory system