Summary
THE PLANNER
1
Somatic Senses Are Related to
Detection of Pressure, Chemicals,
Proprioception, and Touch 228
• Sensation is the conscious or subconscious awareness of
changes in the external or internal environment. A stimulus
causes a receptor to evoke nerve impulses that travel along
specific neural pathways to the brain. Each receptor is spe-
cific for a particular type of stimulus. The brain perceives the
stimulus as a sensation.
2
Some Special Senses Use Receptors That
Detect Chemicals 232
• The chemical senses include smell (olfaction) and taste
(gustation). Specific chemicals bind to receptors in the nose
and on the tongue, where they elicit nerve impulses that
travel to the brain.
Structures of the olfactory epithelium • Figure 8.4
• As shown, the skin has various tactile receptors for touch,
pressure, stretching, warmth, cold, and pain. Upon stimula-
tion, these receptors evoke action potentials in sensory neu-
rons. The action potentials propagate through ascending
pathways in the spinal cord to the somatosensory cortex. •
Skin receptors • Figure 8.2
Merkel
(tactile)
disc
Meissner
corpuscle
Ruffini
corpuscle
Hair root
plexus
Pacinian
corpuscle
Olfactory
tract
Olfactory -
epthelium
Olfactory
bulb
Parts of
olfactory (I)
nerve
Olfactory
receptor
Odorant
• As shown, olfactory receptors are located in the olfactory
epithelium and can detect 10,000 different odorants. Nerve
impulses from olfactory receptors travel through the olfac-
tory tract to the temporal lobe, limbic system, and hypo-
thalamus.
• Proprioceptive sensations allow us to know where our
head and limbs are located or moving. Proprioceptors in
muscle, tendons, and joints sense the positions of the
head and limbs. The vestibular apparatus in the inner ear
senses the orientation of the head and neck. These recep-
tors feed information to the somatosensory cortex and to
the cerebellum.
• Gustatory receptors are located in taste buds on the
tongue and detect five classes of tastes: sweet, sour, bitter,
salty, and umami (meaty, or savory). Nerve impulses evoked
from taste buds travel through cranial nerves VII, IX, and X
to the parietal lobe, limbic system, and hypothalamus.
246 CHAPTER 8
Somatic Senses and Special Senses
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