Physio: Chemical Senses

Question 1

Name the 5 taste sensations and normal thresholds for detection of these sensations.

Answer 1

1. Bitter: 0.008 mM
2. Sour: 2 mM
3. Salty: 10 mM
4. Sweet/Umami : 20 mM

Question 2

What is the reason for the differences in threshold for tasting the 5 different taste sensations?

Answer 2

Things that taste bitter or sour are often noxious stimuli that humans want to avoid. This early detection is a defense mechanism to avoid injury.

Salty and sweet have a higher threshold because we have a primarily carbohydrate diet and need electrolytes.

Question 3

What part of the taste bud has the receptors for the taste molecules?

Answer 3

Gustatory hairs on the top of the gustatory cells.

Question 4

Name a few things that can illicit a bitter taste used to test for super tasters.

Answer 4

PROP (6-n-propylthiouracil)
PTC (phenylthiocarbamide)
Flavanoids (brussel sprouts and kale)

Question 5

How do the taste receptors for salty and sour function?

Answer 5

Salty: sodium ion channel receptor
Sour: proton channel that responds to acid

Question 6

How do Bitter, Sweet, and amino acid taste receptors function?

Answer 6

Bitter:
T2R G-protein coupled receptor signals gustducin to activate PLC, which generates IP3 and opens a calcium channel.

Sweet: Ditto except the receptor is a dimer of T1R2 and T1R3.

AA: Ditto except the receptor is a dimer of T1R1 and T1R3

Question 7

Describe the gustatory tract as it travels from the tongue to its CNS processing center.

Answer 7

1. Chorda Tympani and CN IX fibers in tongue sense taste chemicals.
2. Neuron cell bodies for taste located in geniculate (VII) and petrosal (IX) ganglia.
3. These primary nerve fibers project into the Nucleus of Solitary Tract in the medulla.
   * Synapse*
4. Secondary nerve fibers travel up to the VPM of the thalamus.
   * Synapse*
5. Tertiary neurons travel to the insular cortex in the operculum of the post central partietal cortex.

(UNCROSSED PATHWAY)
(some signals go thru amygdala and perceive how we “feel” about a taste)

Question 8

Gland in the olfactory epithelium that produces mucous.

Answer 8

Bowman’s Gland

Question 9

Type of neuron in the olfactory nerves that sends a signal to the CNS.

Answer 9

Bipolar

Question 10

What is different in the amount of receptor types present in olfactory neurons vs. gustatory neurons.

Answer 10

Gustatory neurons can have multiple receptor types for multiple tastes on one cell.

Olfactory neurons only have 1 type of scent receptor per cell, however, the 1 receptor type can detect multiple scents.

Question 11

Is threshold for smell higher or lower than for taste?

Answer 11

Lower

olfaction is our first line of defense against non-visual noxious stimuli

Question 12

In the olfactory signaling, what is a glomerulus?

Answer 12

A region of the olfactory bulb that receives input from many olfactory neurons that have the same scent receptor.

Question 13

In olfaction, what does a mitral cell do?

Answer 13

Sends the scent signal out to the sensory cortex for interpretation.

Question 14

In olfaction, what is the function of the granule cell?

Answer 14

Refines scent sensation. Adjusts the return signals from the cortex back down to the mitral cells.

Question 15

What do periglomerular cells do in olfaction?

Answer 15

Refine synapses in glomerular tissue.