Sensations Are Evaluated in Various
Places in the CNS
Receptors for the somatic senses communicate with the
somatosensory cortex in the parietal lobe of the cerebrum
through pathways in the spinal cord and brain (see Figure
CONCEPT CHECK
1.
Which
specific receptors sense touching of the
skin?
2.
Where
would you find proprioceptors, and
what do they do?
7.13a). Touch, pressure, vibration, and proprioception are
communicated via one pathway, and pain, cold, warmth,
and itch are transmitted via a separate pathway. In addi-
tion, proprioceptors also pass impulses to the cerebellum
and contribute to its role in coordinating movements.
3.
Where
is the somatosensory cortex located in
the brain?
Some Special Senses Use Receptors
That Detect Chemicals
LEARNING OBJECTIVES
1.
Identify
the structures involved in smell
(olfaction).
2.
Describe
the processes involved in perceiving
odors.
he special senses include smell, taste, sight,
hearing, and balance. Some special senses de-
tect physical phenomena such as light, sound,
or gravity. Because two of the special senses re-
quire the interaction of chemicals
with sensory receptors—
olfaction
(smell) and
gustation
—they are
sometimes referred to as the
chem i-
cal senses.
Also, because the nose and
mouth are connected, the senses of
smell and taste are associated. For
example, when you have a stuffy
nose and cannot smell, you often cannot taste foods. Let’s
start our examination of the chemical senses with olfaction.
Receptors for Olfaction Lie
Within the Nasal Cavity
The nose contains 10 to 100 million receptors for the
sense of smell. These olfactory receptors are located
3.
List
the structures involved in taste (gustation).
4.
Outline
the processes involved in perceiving
tastes.
within the olfactory epithelium and are surrounded by
other cells, including supporting cells and basal cells
(Figure 8.4). Olfactory receptors bind and recognize al-
most 10,000 different molecules, which are collectively
called odorants. The odorants elicit action potentials
within the receptors, and the information is sent via the
olfactory nerves (cranial nerve I) to the olfactory areas of
the brain (temporal and frontal lobes of the cerebrum,
the limbic system, and the hypothalamus) (see Figure
7.10). Because some of the nerve impulses are passed to
the limbic system, certain odors and tastes evoke strong
emotional responses and memories.
Olfactory receptors adapt rapidly to odors. Within the
first second or so of exposure to an odor, approximately
50% of the receptors adapt. The remaining receptors
adapt more slowly. When you first put on perfume or af-
tershave in the morning, there is a strong odor to it, but
that odor seems to “disappear” very quickly. The chemical
is still there, but the nasal receptors lose their ability to
react effectively to it.
T
olfaction
(ol-FAK-
shun) The sense of
smell.
gustation
(gus-TA-
shun) The sense of
taste.
232 CHAPTER 8
Somatic Senses and Special Senses
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