Ch 8: The Chemical Senses

What are the 5 tastes and what is their location on the tongue?

• Bitter → Back of tongue

• Sweet → Tip of the tongue

• Sour → Front sides

• Salty → Back sides

• Umami → Middle of tongue

Why do we lick ice cream cones?

Because it activates sweet receptors on the tip of the tongue

What are the different shapes of papillae?

• Foliate papillae → ridges

• Vallate papillae → pimples

• Fungiform papillae → mushrooms

Describe a taste bud.

• Each taste bud contains 50-150 taste receptor cells

• Visible only with a microscope

• Have basal cells that surround the taste receptor cells

• Have a set of gustatory afferent axons

• A person typically has 2000-5000 taste buds, as few as 500 and as many as 20000

Describe the connectivity of taste cells.

• Taste cells form synapses with the endings of the gustatory afferent axons near the the bottom part of the taste bud

How does a receptor potential lead to neurotransmitter release?

1. When an appropriate chemical activates a taste receptor cell, its membrane potential changes, usually by depolarizing (receptor potential)

2. If that receptor potential is large enough, some taste receptors may fire action potentials.

3. Depolarization causes voltage-gated calcium channels to open

4. Ca2+ enters the cytoplasm, triggering the release of transmitter molecules

Describe the transduction mechanisms for salty.

Describe the transduction mechanisms for sweet.

Write out the transduction pathway for bitter/sweet/umami from binding to the receptor to neurotransmitter release.

Write the central taste pathway from the cranial nerves to the cortex.

What happens when we lesion the VPM/gustatory cortex, hypothalamus/amygdala?

Describe population coding for taste.

What is a pheromone?

How do pheromones differ in animals and humans?

What is the role of olfactory epithelium?

What is the role of mucus?

Describe the intracellular signaling triggered by an odorant binding.

What makes us stop smelling a new smell we encounter?

Describe population coding for odorants.

Describe glomeruli and how they relate to a sensory map.

Describe the olfactory pathway from receptor cell to cortex.

What makes the olfactory pathway different from the other senses?

Describe olfactory maps.