Module 7 Flashcards
characterize the peripheral and central organization of the gustatory system
discuss sensory transduction in gustatory receptor cells
describe information coding in the gustatory system
characterize the peripheral and central organization of the olfactory system
discuss sensory transduction in olfactory receptor cells
describe information coding in the olfactory system
can an odor be responded to at different concentrations?
yes, ex. indole smells of flowers at low concentrations and purtrid at high concentrations (could be a result of affinity to receptors)
structure of olfactory system
- odorants (inhaled in)
- layer of mucus, within mucus, are the olfactory cilia, the chemicals must dissolve in the mucus
- the cilia are connected to an olfactory knob
is an odor always detectable as the same scent?
no, can depend on concentration and how affects receptors
process of olfaction
- scent inhaled, dissolved in mucus layer
- binds to olfactory cilia attacked to ORNs
- travels through olfactory knob and affects mature ORNs
- the neurons innervate glomeruli which contact downstream mitral cells
- mitral cels project to the olfactory cortex
what are glomerulus?
circles of coalescing neurons, neurons with same receptor projects to the same glomerulus, 25,000 ORN’s can project to a single glomerulus
how does olfactory system distinguish between smells?
activates receptors with the same features as molecule, molecule can have multiple features, but each feature will end together at a single glomerulus
what are basal cells?
produce stem cells as developing ORNs that replenish damaged mature ORNs
what does bowman’s gland do?
secretes mucus
what is the purpose of mucus?
helps protect against harmful odorants, although more mucus decreases olfactory acuity
where do ORNs receive signals?
ONLY at the cilia
odorant receptors
most are GPCRs, 7 TM receptor
process of olfactory receptor activation
- activated by ligand
- Ga (in this case, Golf), binds to GPT and with ATP at adenyl cyclase III, activates CAMP (second messenger)
- activates ion-gated channel leading to depolarization and activation other ion channels and exchangers (positive in, - out)
- depolarizes membrane
combinatorial odor code
can activate multiple receptors based on how many features a molecule has (most odorants activate multiple glomeruli)
how does a signal from the mitral cell reach the cortex?
afferent inputs: OSN to GL to mitral cells to olfactory cortex
what inhibition are signals from mitral cells to olfactory cortex faced with?
granule cells: top-down inputs and map onto mitral cells, mitral cells can release glutamate which causes granule cell to release GABA back at mitral cell, essentially turning it off (reciprocal synapse bc can send and receive info)
Periglomerular cell: does the same thing, but from OSN to mitral cells
how do chemical signals map onto the pyriform cortex?
aren’t many patterns when just a few receptors activated, but when multiple receptors activated, can see a specific pattern that is specific to each molecule
*added caged glutamate as opposed to full glutamate bc after to activate receptors
the model of pyriform cortex activation in olfactory system
need all receptors of molecules’ features to fire to activate cortical response
what are olfactory bulb targets?
The pyriform cortex, olfactory tubercle, amygdala, and entorhinal cortex are mapping on to…
orbitofrontal cortex, thalamus, hypothalamus, hippocampal formation
gustatory system nerves
- gustatory cells of the tongue, go to cranial nerves
- nucleus solitarius maps to thalamus
- thalamus maps to primary gustatory cortex in insula of cerebrum
where are taste buds?
tongue, inside cheeks, soft palate, pharynx, epiglottis
what is the lingual papillae
to distinguish food texture, taste
classes of taste
bitter, sour, sweet, meaty (umami), salty
elements of a taste bud
receptors for each class of taste (taste cell), supporting cells, taste pore as taste hairs at the top of the taste bud (this is the receptor surface), and the other side has synaptic vesicles and synaptic nerve fibers that innervate the taste buds, there are also basal cells to replace damaged cells
how can things be tasted?
molecules must dissolve in saliva and flood a taste pore
why is salty taste important?
important for electrolyte balance
why is sweet taste important?
indicates carbs and foods with more calories, as calories are needed for survival
why is sour taste important?
acids, citrus fruits
why is bitter taste important?
to keep you from eating toxic things (ex. spoiled foods, nicotine, caffeine, morphine)
why is umami taste important
savory meat taste, protein
are hot peppers a taste?
no just act on TRPVI in nociceptors, not taste buds
how is taste innervated?
olfactory eventually converges with gustatory pathway
where is gagging on the tongue?
at back of tongue
salty receptors
sodium ion chanel
sour receptors
ph (H+) ion channel which inhibit inward K+ channel
sweet receptors
TIR2 and TIR3 proteins (dimerize into a fly trap)
amino acid (umami) receptors
TIR1 and TIR3 proteins (dimerize into a fly trap)
bitter receptors
T2R protein
which receptors have high threshold for action potential in gustatorial system?
salty, sour, and sweet
which receptors work via IP3 causing Ca influx via TRPM5 channels?
sweet, umami, bitter
how to block a channel
if KO just one protein in class receptor, it doesn’t work
type 1 taste cells
glial cells, supporting other epithelial cells can regulate ionic environment
type 2 taste cells
chemosensory receptor cell for sweet, bitter, umami, salty tastants has 1 or 2 classes of cell receptors (excitable and releases ATP and channel synapse)
type 3 taste cells
chemsensory receptor for sour tastants, releases nt (serotonin)
type 2 cells in action
2 paths:
the first…
1. salty ions glow through Na+ ion channel
the second…
1. sweet, bitter, or umami ions bind to the GPCR, and the a and g subunits bind to PLCb2 on the membrane
2. this releases IP3 which acts on Ca2+ on ER
3. the Ca2+ channel opens and causes the TRPM5 channel to open, depolarizing the membrane
they converge:
1. voltage gated ion channel opens as a result of the depolarization
2. this causes the CALHM ATP channel to open and release ATP
3. the ATP bind to the gustatory afferent axon at the P2X adenosine receptor
4. this propogates depolarization in the neuron
type 3 cells in action
- sour acid enter via H+ ion channel (depolarizing the cell)
- this causes the voltage-gated ion channel to open and the voltage-gated Ca2+ channel to open
- the Ca2+ cause the serotonin vesicles to merge with the membrane and rush across to the gustatory afferent axon serotonin receptor
what level of nutrients need to be present to promote a response?
large amount, because body only responds to large levels of essential nutrients
label line coding neural theory
taste neurons each have a dedicated specific taste quality carried by a unimodal taste receptor cell to cortex, each are represented individually in a taste bud
across neuron pattern neural theory
perception of taste from a combination of multiple neurons, individual neurons can respond to multiple tastes (don’t have to be specialists)
which theory of neural coding theory prevails?
evidence for both
cranial nerve pathways
cranial nerve VII: input from first 2/3 of tongue, sends to ganglion VII
cranial nerve IX: input from posterior 1/3 of tongue, sends to ganglion IX
cranial nerve X: input from pharynx, upper esophagus, sends to ganglion X
where do cranial nerves go?
- taste buds
- cranial nerves
- ganglion
- nucleus of the solitary tract (kind of behind brain stem at top of spine)
- VPMpc of thalamus to insular and frontal gustatory cortices OR hypothalamus and amygdala to insular and frontal gustatory cortices
old thinking of gustatopic map
spatial coding
specific cells activated in cortex based on class of neurons
current thinking of gustatopic map
temporal coding
behavior of neurons (firing rate) impacts the perception of taste class (firing rate over time affects perception)
