The Special Senses

• Gustation (taste)

• Olfaction (smell)

• Hearing

• Equilibrium (balance)

• Vision (sight)

Chapter 17

The Chemical Senses: Taste and Smell

• The receptors for taste and smell are chemoreceptorschemoreceptors

• 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

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Olfactory PathwaysFrom 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