The Special
Senses
Chapter 17
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Gustation (taste)
Olfaction (smell)
Hearing
Equilibrium (balance)
Vision (sight)
The Chemical Senses:
Taste and Smell
• The receptors for taste and smell are
chemoreceptors
• Chemoreception involves chemically gated ion
channels that bind odorant or food molecules
• Depolarization of the receptor cell causes it to
release neurotransmitter that stimulates nerve
impulses in the sensory neurons
Taste
Taste Chemoreceptors - Taste Buds
• Located
mostly
on
papillae
of
tongue
Fig. 17.7
Basic Tastes
Simplified Version:
• Sweet
• Sour
• Salty
• Bitter
New Tastes:
• Umami = savory (like MSG)
• Taste of fat
• Taste of “heat” from chili
peppers
Sensory Pathways for
Taste
• From facial nerves to medulla
oblongata, then thalamus, then
sensory cortex
• Afferent impulses of taste also
stimulate reflexes which
promote digestion
Smell
Location of Olfactory Receptors
In olfactory
epithelium in nasal
cavity
Transduction of Smell
• Humans can
distinguish thousands
odors
• The binding of an
odorant molecule to a
specific receptor
causes gated Na+
channels to open,
leading to
depolarization
•
Olfactory Pathways
From cranial nerve I (olfactory) to:
1. the olfactory cortex where smells are consciously
interpreted and identified
2. the limbic system where smells elicit emotional
responses
3. sympathetic nervous system & stimulate
digestive processes