Lecture 4: Physiology of Olfaction and Gustation Flashcards
What is anosmia?
Loss of smell
What is aguesia?
Loss of taste
What tastants trigger the release of serotonin?
Sour and salty
Conventional calcium-triggered release
What tastants trigger the release of ATP?
Sweet, umami, and bitter
(SUB sandwiches give you energy)
Calcium triggered release of ATP
What stimutas sour tastant?
What does it recognize?
Hydrogen Ions
Presence of dietary acids (can be found in spoiled foods)
What stimulates salty tastant?
Na+ binding ENaC
What stimulates sweet tastant?
What can it recognize?
Sugars binding GPCRs
Presence of carbohydrates that serve as energy sourse
What stimulates umami tastant?
What does it recognize?
Glutamate binding mGluR4 (GPCR)
Food’s protein content due to presence of glutamate
What stimulates bitter tastant?
Various compounds binding GPCRs
Which tastant binds its GPCR with very high binding affinity?
Bitter (avoid poison)
What type of cells are olfactory cells and what NT does it release?
Bipolar Neurons that release glutamate
What is activated by the G-olf GPCR pathway?
Adenylyl Cyclase III which increases cAMP, activating CNGC
What happens when CNGC channels are open?
Cation influx, resulting in depolarization and opening of a calcium-gated Cl- channel
What are the two main ways that adaptation to odorant stimulation occurs?
- Sensitivity of CNGC to cAMP decreases –> decreased cation influx –> decreased depolarization
- Inactivation by receptor phosphorylation
What happpens to gustatory and olfactory sensitivity with age?
Decreases
Why you can tolerate more salt and spices as you are older
What activates the endogenous opioid system?
Sweet-tasted induced beta-endorphin release
How is bitter taste in medicine blocked?
Sodium salts can sppress bitter taste at receptor
Where do the afferent neurons (1st order) coming from the taste buds terminate?
Nucleus Tractus Solitarius (gustatory area)
Receives multiple sensory inputs
In the ascending taste pathway, where do the 2nd order sensory neuron cell bodies arise?
Where do they terminate?
Arise from nucleus tractus solitarius
Terminate in VPM nucleus of thalamus
What is the role of the ventral posterior medal nucleus of thalamus?
Identifying the discriminative aspects of taste
Where do the 3rd order neurons of the ascending taste pathway arise?
Where do they terminate?
Arise from VPM and travel through Posterior Limb of IC
Terminate in Gustatory Cortex
- Insular Taste Cortex
- Operculum of Frontal Cortex
- Postcentral Gyrus
What role does the hypothalamus and amygdala play with taste?
Emotional context to eating and memories of eating
Role in hunger
What role does the orbitofrontal cortex have in the taste pathway?
Interpretation of taste, olfaction, and visual cues regarding food
Appreciation of flavor, food reward, control of feeding
How do olfactory receptor neurons relay information to olfactory tract?
- Olfactory neurons synapse onto glomeruli cells and release GABA + glutamate
- Local interneurons release GABA to increase specificity of signal
- Mitral and tufted cells will project to olfactory tract
- Granular cells release GABA to increase specificity again
What is the anterior olfactory nucleus?
Relay station to ipsilateral and contralateral cortices
Poorly understood
What is the function of the piriform cortex and lateral hypothalmus?
Control of appetite
How olfactory input influences appetite and hunger
What is the function of the piriform cortex and medial orbitofrontal cortex?
Integration of sight, smell, and taste of food
Appreciation of the flavor of food
What is the function of the anterior cortical amygdaloid nuclei?
Emotional learning
Olfactory fear conditioning
What is the function of the periamygdaloid cortex?
Integration of the emotional aspect of food as elicited by odor
More about response
What is the function of the entorhinal cortex and hippocampus?
- Memory formation and how olfactory input facilitates both memory and recall
- Connections within the limbic system and entorhinal cortex are responsible for the highly evocative experience of memory upon odor sensation.
