Taste & Smell

Question 1

What are the different papillae on the tongue? What kind of receptors are found in each?

Answer 1

Filiform (flame-shaped): pain and temperature
Fungiform (pink dots on anterior tongue): taste
Circumvallate (large papillae, inverted V on back of tongue): taste
Foliate (In small trenches on sides of posterior tongue): taste

Question 2

What is a supertaster?

Answer 2

Individual with higher density of fungiform papillae than normal, have a heightened response to taste.

Question 3

What are the main tastes and their receptors?

Answer 3

Salty: ionotropic, sodium
Sour: ionotropic, hydrogen
Sweet: metabotropic (G protein), second messenger is cAMP
Bitter: metabotropic (G protein), second messemger is IP3.
Umami: metabotropic (G protein), second messenger unknown

Question 4

How does intestinal peptide GLP-1 affect taste reception?

Answer 4

GLP-1 is produced and released from taste cells in response to food.
Alters responsivity to taste

Question 5

Describe the taste pathway from the tongue regions to the insula.

Answer 5

Tongue has three regions with distinct innervation:
Anterior 2/3 (facial), posterior 1/3 (glossopharyngeal), palate and epiglottis (vagus) –>
Solitary nucleus in the medulla –>
Ventral posterior medial nucleus (VPM) of thalamus (ipsilateral) –>
primary gustatory cortex (insula)

Question 6

Describe the olfactory receptor cells. How do odorants activate receptor cells?

Answer 6

Receptor cells are bipolar neurons whose axons project through the cribriform plate into the nasal cavity, where microvilli with receptors extend into a mucus layer.
Only mucus-soluble odorants can activate receptors.

Odorants activate Na/Ca and Cl ion channels on the microvilli.

Humans have about 300 types of odorant receptors.

Question 7

How do they stimulate receptor adaptation?

Answer 7

Sensory adaptation occurs within a minute. Relies largely on Ca to close odorant receptor ion channels and repolarize receptor cells, shutting down the response to the odorant.

Question 8

Describe the structure and location of the piriform cortex and how it processes olfactory information.

Answer 8

A primitive cortex on the medial surface of the temporal lobe (in the lateral fissure).
Neurons respond to an odorant mixture.
We only experience one odor event at a time.
Also undergoes habituation, in addition to adaptation at the level of receptor cells, so that new/multiple odorants can be detected .

Question 9

Describe how the amygdala and orbitofrontal cortex process olfactory information.

Answer 9

The amygdala links events that have a similar emotional valence. Olfactory memories are more emotional than others.
The orbitofrontal cortex governs your subjective experience of an odor, whether it is pleasant or unpleasant. Associates olfactory sensation with other sensory inputs to determine how you value something, some food for example.

Question 10

Describe how intranasal substances such as viruses and peptides are transported to the CNS.

Answer 10

Olfactory receptors are in direct contact with the CNS and the outside world. 
Viral particles (e.g. measles) can be transported along axons to the olfactory bulb and cross synapses into the brain. 
Bacteria (e.g. pneumococci) can penetrate the mucosa into the subarachnoid space and cause meningitis. 
Peptides (intranasal insulin) are transported extracellularly along axon bundles to the olfactory bulb.