Physiology of Taste and Smell Flashcards
What occurs when taste receptors are signalled?
usually depolarizing –> opens voltage-gated Ca channels –> NT release
What NT do Sour and Salty taste receptors release and what does it signal?
Serotonin –> post-syn primary gustatory neurons
What NT do Sweet, Bitter, and Umami receptors release and what does that stimulate?
(these things give you energy)
ATP –> post-syn primary gustatory neurons
or pre-synaptic salty/sour recptor cells –> 5-HT
or Autocrine signaling
What is P2Y?
receptor for ATP
on SUB cells or Sour/Salty cells
What is P2X?
ATP receptor on SUB cells
(can do autocrine signaling)
How is salt allowed into taste receptors?
Na goes in via ENaC –> diffuses down gradient into cell –> depolarizes membrane –> increased Ca –> 5HT released
What molecule do sour foods use to stimulate taste receptors and what is its effect?
H+ from the acid –> inhibits potassium channels from flooding more + charges –> depolarization –> increased Ca –> 5-HT released
What type of receptor binds sweet, umami, and bitter flavors?
GPCR
all are Gq
What is the general mechanism of SUB taste cell signaling?
SUB molecule binds Gq GPCR –> PLC- IP3 –> increased intracellular Ca –> TRPM5 activation –> Na in –> depolarization –> release of ATP through PanxI channels = NT release
What is the specific receptor for umami flavors?
mGluR4 = GPCR for glutamate
Where are secondary sensory neuron cell bodies for the ascending taste pathway?
nucleus tractus solitarius
How does the brain integrate visual, somatosensory, olfaction, and gustatory stimuli?
VPM –> gustatory cortex –> orbitofrontal cortex
How does the brain do emotion and memory associated with eating/
Gustatory cortex –> amygdala
How does the brain integrate homeostatic mechanisms of eating (hunger)?
Hypothalamus –> nucleus tractus solitarius
Where do medularry reflex arcs occur (salivating, swallowing, etc)?
nucleus tractus solitarius
What type of cells are olfactory cells?
What are their receptor proteins?
bipolar neurons
GPCRs = Gs
What happens when an odorant binds its receptor?
binds Golf –> increased cAMP –> opes CNGC –> cation influx –> depolarization
How does odorant desensitization occur?
odorant persists –> sensitivity of CNGC to cAMP decreases –> reduces cation influx
or inactivated by receptor phophorylation
What is the relationship btw the number of odor receptors and a glomerulus?
one olfactory neuron expresses the same odorant receptor on all of its cilia
neurons with similar receptors all put their axons into the same glomerulus
How do we detect a ton of different odors w/ only ~350 odorant receptors?
one odorant can bind more than one type of OR
Patterns of OR binding –> different smells
What NT do granular cells and periglomerular cells release?
GABA –> increases specificity of signal
What type of NT do ORNs release?
glutamate
What is the major difference btw taste receptors and olfactory receptors?
taste = modified epithelial cells
olfactory receptors = neurons
What part of the brain is essential for perception of flavor?
gustatory and olfactory cortices =
medial orbitofrontal cortex
What path integrates taste, sight and smell, and allows for appreciation of flavor (but not identification)?
piriform cortex –> thalamus –> medial orbitofrontal cortex
What does the anterior olfactory nucleus do in smell?
poorly understood
goes to bilateral cortices and olfactory bulbs
Where do all parts of the olfactory cortex go?
DILO
DM thalamic nucleus
Insular and orbital cortex
lateral hypothalamus
olfactory bulb
What is the extra place tha the lateral entorhinal cortex go and what is encoded here?
hippocampus
memory formatio and recall related to smell
What does the piriform cortex help encode?
control of appetite
What does the anterior cortical amygdaloid nucleus do?
emotional learning, smell fear conditioning
What does the periamygdaloid cortex do?
integrates emotional aspects elicited by odor
