Chemosensation

Question 1

In a subset of people, loss of smell is a symptom of _____________.

Answer 1

neurodegenerative disease

Question 2

Loss of taste is called _____________. Loss of smell is _________.

Answer 2

ageusia; anosmia

Question 3

Which is more common, loss of taste or smell?

Answer 3

Smell

Question 4

Which cranial nerves innervate the tongue?

Answer 4

Anterior 2/3: facial (VII)
Posterior 1/3: glossopharyngeal (IX)
Larynx: vagus (X)

Question 5

There are five tastes that we can sense. List them and give the type of channel that mediates their signals.

Answer 5

Sour: ion
Salty: ion
Sweet: GPCR
Bitter: GPCR
Umami: GPCR

Question 6

Describe the mechanism of the GPCR receptors.

Answer 6

Upon binding a ligand, the beta-gamma unite activates phospholipase which activates IP3; this releases sarcoplasmic calcium that opens sodium channels (TrpM5) and leads to depolarization.

Question 7

The gustatory neurons first synapse on ____________.

Answer 7

the solitary nucleus (upper-mid medulla), which projects axons to the VPM in the thalamus

Question 8

After a ligand binds to an olfactory receptor, what happens?

Answer 8

A GPCR second-messenger cascade (starting with G-alpha) leads to an increase in cAMP; the increased cAMP binds to calcium channels, allowing in a small amount of calcium. Calcium bind to chloride channels and the outflow of chloride depolarizes the cell.

Question 9

The olfactory tracts lead to what gyri?

Answer 9

The piriform gyri of the medial temporal lobes and thence to the orbitofrontal (conscious smell)

The entorhinal cortex of the hippocampus (memory)

Amygdala/hypothalamus (visceral reaction)

Question 10

Strong chemical smells and spices activate the ________ nerve.

Answer 10

trigeminal

Question 11

The pheromone-sensing organ present in many animals is called the _____________.

Answer 11

vomeronasal system

Question 12

What are the three kinds of chemosensory cells in the body?

Answer 12

Olfactory: bipolar neurons
Gustatory: modified epithelium that synapses on ganglion cells
Chemesthesis: free nerve ending of trigeminal ganglion

Question 13

List the three types of papillae and their locations.

Answer 13

Fungiform: anterior top
Foliate: sides
Circumvallate: posterior

Question 14

Like the photoreceptors, taste cells also _____________.

Answer 14

fire in response to multiple sensations (integrating them to avoid hypersensitivity)

Question 15

The primary way of processing odor quality is through ______________.

Answer 15

glumerular (little bulbs on the other side of the ethmoid bones) integration of odors