Physiology of Olfaction and Gustation (Pierce) 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
Cations trigger the release of _______
GPCRs trigger the release of _______
- Serotonin
- 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 Epithelial sodium channels (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
What type of cells are olfactory cells and what NT does it release?
Bipolar Neurons that release glutamate
What type of receptors do olfactory cells bind to and what are they called.
GPCR’s
Golf receptors
What is activated by the G-olf GPCR pathway?
Adenylyl Cyclase which increases cAMP. cAMP activates cyclic-nucleotide gated channels (CNGC) that allow Na+/Ca2+ to enter the cell, depolarizing it.
What happens when CNGC channels are open?
Cation (Na+/Ca2+) influx, resulting in depolarization that opens up Ca2+/Cl- channels that provide remainder of depolarization needed to generate appropriate receptor potential to achieve action potential
What is the sensory transduction pathway in olfactory neurons
- Odorants diffuse into nasal mucus, binds receptor proteins on olfactory cilia, and activates olfactory cell
- Olfactory receptor proteins are GPCR’s called G olf
receptors - Uses second messenger transduction systems (cAMP) 4. This opens cyclic-nucleotide gated channels (CNGC): allowing Na+ and Ca2+ to influx into cell.
- Depolarization occurs.
- Ca2+-gated Cl- channels opens that provides remainder of depolarization needed to generate appropriate receptor potential to achieve action potential
What are the main ways that adaptation to odorant stimulation occurs?
- Enzymatic break down of cAMP reduces receptor potential
- Binding of calcium to calmodulin reduces the affinity for the channel to cAMP
- Phosphoryzation of the odorant receptor which modifies its sensitivity to odorants.
Which tastant binds its GPCR with very high binding affinity?
Bitter (avoid poison)
What happpens to gustatory and olfactory sensitivity with age?
Decreases
Why you can tolerate more salt and spices as you are older
How is the analgesic effect of sweet-solutions explained
Sweet-tasted induced beta-endorphin release, activating the endogenous opiod system
How is bitter taste in medicine blocked?
Sodium salts can suppress bitter taste at the level of the bitter-receptor
At what level does sugar suppress the sense of bitterness
At the cognitive level
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 ventral posterior medial (VPM) nucleus of thalamus
What is the role of the ventral posterior medal nucleus of thalamus?
Relay station for taste perception. Begins discriminative aspects of taste
Where do the 3rd order neurons of the ascending taste pathway arise?
Where do they terminate?
Arise from VPM and terminate in Gustatory Cortex
What brain region does the gustatory cortex connect with to allow for the integration of visual, somatosensory, olfaction and gustatory stimuli
orbitofrontal cortex
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
Where do neurons that arise from the gustatory cortex send their axons
Amygdala
Orbitofrontal cortex
What role does the amygdala play with taste?
Affective aspects of eating, emotional contex to eating & memories of eating
What role does the hypothalamus play with eating
Integrates homeostatic mechanisms of eating (such as hunger)
How do olfactory receptor neurons relay information to olfactory tract?
- Olfactory neurons synapse onto glomeruli cells and release glutamate
- Periglomerular cells (local interneurons) release GABA to increase specificity of signal
- Mitral and tufted cells will project to olfactory tract
- Granular cells (local interneurons) release GABA to increase specificity again
What does the olfactory cortex consist of
Anterior Olfactory nucleus
Olfactory tubercle
Piriform cortex
Anterior cortical amygdaloid nuclei
Periamygdaloid cortex
Lateral enthorhinal cortex
What is the anterior olfactory nucleus?
Relay station to ipsilateral and contralateral cortices
Poorly understood
What is the function of the piriform cortex as it routes to the lateral hypothalamus
Control of appetite & hunger
What is the function of the piriform cortex as it routes to the thalamus and then to the 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 as it projects to the 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.
