449
CHAPTER TWELVE
Nervous System III
FIGURE 12.8
A light micrograph of some taste buds (arrows) (225×).
Taste Sensations
The f
ve primary taste sensations are sweet, sour, salty, bit-
ter, and umami (oo-mom
ee). Each oF the many fl
avors we
experience results From one oF the primary sensations or
From a combination oF them. The way we experience fl
avors
may also refl ect the concentration oF chemicals as well as
the sensations oF smell, texture (touch), and temperature.
±urthermore, chemicals in some Foods—such as capsaisin
in chili peppers—may stimulate pain receptors that cause a
burning sensation.
Experiments indicate that each taste cell responds to
one taste sensation only, with distinct receptors. Taste cells
For each oF the f ve taste sensations are in all areas oF the
tongue, but are distributed such that each sensation seems
to arise most strongly From a particular region. Due to the
distribution oF taste cells, responsiveness to particular sen-
sations varies From one region oF the tongue to another.
Sensitivity to a sweet stimulus peaks at the tip oF the tongue,
whereas responsiveness to sour is greatest at the margins oF
the tongue, and to bitter at the back. Receptors particularly
responsive to salt are widely distributed.
Sweet receptors
are usually stimulated by carbohydrates,
but a Few inorganic substances, including some salts oF lead
and beryllium, also elicit sweet sensations. Acids stimulate
sour receptors.
The intensity oF a sour sensation is roughly
on taste hair surFaces. This binding alters membrane polar-
ization, generating sensory impulses on nearby nerve f bers.
The degree oF change is directly proportional to the concen-
tration oF the stimulating substance.
Papillae
Epithelium
of tongue
Taste cell
Taste hair
Supporting
cell
Taste
pore
Sensory
nerve fibers
Connective
tissue
Taste buds
(a)
(b)
FIGURE 12.7
Taste receptors. (
a
) Taste buds on the surface of the
tongue are associated with nipplelike elevations called papillae.
(
b
) A taste bud contains taste cells and has an opening, the taste pore,
at its free surface.
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