GUSTATION

Transduction Sequence

1. Chemical stimulus dissolves in oral fluid, diffuses into taste pore, and binds with receptor on microvillus of receptor cell

2. Different submodalities depolarize submodality-specific taste cells by different mechanisms

a. Na⁺ acts by entering cell by Na-selective channel

b. H⁺ depolarizes receptor by reducing P_K of potassium channel

c. sweet and bitter substances act by G-protein second messenger mechanisms

3. Taste cell depolarization releases excitatory neurotransmitter at its base, exciting the afferent axon (taste cell itself does not generate AP)

CODING

1. Theories: Conclusion: several receptor types, each responsive to a single class of tastants (labeled line) or a number of cell types respond to each tastant class and the precise taste is recognized from the population discharge pattern (pattern hypothesis)

Figure: Responses of 24 different taste first-order sensory fibers.
A. Application of two different but similarly-tasting substances
B. Two substances with different tastes applied to the receptors