Physiology of Gustation and Olfaction

Question 1

Sour taste stimulated by what ions and release what NT

Answer 1

H+ ions

Serotonin

Question 2

Salty taste stimulated by what ions and release NT

Answer 2

Na+ binding ENaC

Serotonin

Question 3

Sweet taste stimulated by what molecules and release what NT

Answer 3

Sugars binding GPCRs

ATP

Question 4

Umami taste stimulated by what molecules and release what NT

Answer 4

Glutamate binding mGluR4 GPCR

ATP

Question 5

Bitter taste stimulated by what molecules and release what NT

Answer 5

Various compounds binding GPCR

ATP

Question 6

Taste bud cells

Answer 6

Specialized epithelial cells
Chemosensory transduction is initiated in apical domain and electrical signals generated in basal domain
Taste receptor proteins located on microvilli on apical surface

Question 7

Olfactory neurons

Answer 7

Bipolar neurons that release glutamate as primary NT
Odorants bind and activate odorant specific G protein which activates adenylate cyclase and eventually leads to Ca2+ gated Chloride channels opening

Question 8

Sensitization to a smell

Answer 8

When pleasant or pungent odors are presented, the odorant receptor itself can become phosphorylated, which modifies its sensitivity to odorants
This plays a role in perceived changes in awareness of smells
Sensitivity of the CNGC (cyclic nucleotide gated channel) to cAMP will also decrease which reduces cation influx and assists in sensitization
Ca binding calmodulin will cause reduced sensitivity for the channel to cAMP

Question 9

Bitter taste ligands affinity

Answer 9

Bitter taste can be associated with poisons, and therefor the ligands that stimulate the GPCRs for bitterness bind with very high affinity

Question 10

Sweet tastes and analgesics

Answer 10

Sweet tastes can be used as an analgesic for newborns during minor, painful procedures. It will typically calm the child and reduce heart rate for several minutes
It is speculated that sweet taste causes beta-endorphin release, activating endogenous opioid system

Question 11

Hiding bitterness in drugs

Answer 11

Sodium salts can be added to suppress the bitter taste at the level of the receptor.
Sugars suppress the sense of bitterness at the cognitive level

Question 12

Processing of taste in nucleus of the solitary tract

Answer 12

Receives multiple sensory inputs from vagus nerve that relays info about the viscera
Early site of gustatory and visceral info

Question 13

Processing of taste in ventral posterior medial nucleus of the thalamus

Answer 13

Relay station for taste perception

The discriminative aspects of taste are processed here

Question 14

Gustatory cortex

Answer 14

Consists of the insular taste cortex, operculum of frontal lobe, post central gyrus

Question 15

Processing of taste in the hypothalamus and amygdala

Answer 15

Amygdala gives emotional context and memories of eating
Hypothalamus integrates mechanisms of eating such as hunger
Interplay b/w eating and the calming effects of food take place in the limbic and reward system

Question 16

Processing of taste in the orbitofrontal cortex

Answer 16

This area integrates visual, somatosensory, olfaction and gustatory stimuli to collectively appreciate the flavor of food
Flavor does not = taste, it requires the additional senses listed above

Question 17

Granular cells in olfactory mucosa and bulb

Answer 17

Local interneurons that release GABA and increase specificity of signal

Question 18

Mitral cells in olfactory mucosa and bulb

Answer 18

Project to the olfactory tract along with tufted cells

Synapse in the olfactory glomerulus with olfactory receptor neurons

Question 19

Periglomerular cells in olfactory mucosa and bulb

Answer 19

Local interneurons that release GABA and increase specificity of signal near the olfactory glomerulus

Question 20

Olfactory neurons

Answer 20

Synapse onto glomeruli and release glutamate

Question 21

Anterior olfactory nucleus

Answer 21

Relay station to ipsi and contralateral cortices

Poorly understood

Question 22

Piriform cortex and lateral hypothalamus

Answer 22

Control of appetite and how olfactory input influences appetite and hunger

Question 23

Piriform cortex and medial orbitofrontal cortex

Answer 23

Integration of sight, smell and taste of food

Appreciation of the flavor of food

Question 24

Anterior cortical amygdaloid nuclei

Answer 24

Emotional learning, olfactory fear conditioning

Question 25

Periamygdaloid cortex

Answer 25

Integration of the emotional aspect of food as elicited by odor

Question 26

Entorhinal cortex and hippocampus

Answer 26

Memory formation and how olfactory input facilitates both memory and recall
Connections within limbic system and entorhinal cortex are responsible for the highly evocative experience of memory upon odor sensation

Question 27

Parkinsons and olfactory neurons

Answer 27

Olfactory neurons are among the first to demonstrate pathology, sometimes years before a motor deficit is manifested
Olfactory testing as a biomarker for neurodegenerative diseases is becoming increasingly common practice