Taste and Smell Flashcards
what are the 5 flavors
salt, sweet, umami, sour, butter
what tastes savory
amino acids
what tastes bitter
simple ions and complex organic molecules
what tastes sweet
sugars/ carbohydrates, proteins, artificial sweeteners
what tastes sour
acid
parts of the throat
pharynx, epiglottis
anatomy hierarchy of tounge
papillae, taste buds, taste cell
how many taste buds are in 1 papillae
papillae (visible to naked eye) have 1-100’s of taste buds (microscopic)
how many taste cells in 1 taste bud
50-150 taste cells
taste pore
pore on surface of the tongue that connects to taste cells
gustatory afferent axons
transmit taste information from the tongue and other areas of the oral cavity to the brain via cranail nerves for higher level processing
2 types of taste cells
broadly tuned and taste selective cells
broadly tuned cells
respond to 2 or more taste stimuli
taste selective cells
detects only 1 taste stimuli
taste cells vs axon response
follow same firing pattern as taste cells
which tastes use ion channels
salty (Na+) and sour (H+)
which tastes use g protein coupled receptors
sweet, savory, bitter
ion channel mechanism
Na+ into the cell, increase conc, depolarize cell, Ca2+ channels influx (voltage gated ion channel), vesicle fuse and transmitter release
H+ into cell AND binds to K+ channel to stop K+ from leaving -> depolarization and action potential
g coupled protein receptors depolarization mechanism
g proteins stimulate enzyme phospholipase C which produces IP3, IP3 opens Na+ channels, depolarization
g coupled protein receptors transmitter release mechanism
IP3 triggers release of Ca2+ from intracellular storage sites, activates ATP permeable channel, ATP transmitter
bitter receptors
-25 types
-2 T2R proteins
sweet receptors
- only 1 type
-2 T1R proteins
savory receptors
- only 1 type
-2 T1R proteins
cranial nerve VII
facial nerve; info from anterior 2/3 of tongue
cranial nerve IX
glossopharyngeal nerve; posterier 1/3 tonguec
cranial nerve X
vagus nerve; throat regions (glottis, epiglottis, pharynx)
taste pathway to primary gustatory cortex
afferent axons from tongue and throat, left gustatory nucleus of solitary tract (medulla), VPM (Ventral Posteromedial) thalamus, primary gustatory cortex
where is the primary gustatory cortex located
insula
is information contralateral or ipsilateral
ipsilateral
what path is left gustatory nucleus
nucleus of solitary tract
where are broadly tuned cells commonly located in the gustatory system
nucleus of solitary tract (gustatory nucleus in brainstem)
where is higher order taste processing; secondary gustatory cortex
orbitofrontal cortex
what 3 things to cells in gustatory cortex respond to
- taste stimuli
-conc of taste stimuli
-satiation
how do we allow for better discrimination of taste stimuli
population coding/ data from a population/group of partially overlapping broadly tuned cells
topographic map of gustatory system
many gustatory cortex (GC) cells preferentially respond to 1 taste stimuli (selective) and there’s different regions can be shown via proposed topographic map
ratio of broadly tuned vs selective cells in GC
unknown atm
what do studies shown about cells in orbitofrontal cortex (secondary gustatory cortex) regarding prediction
can predict reward before it happens; reward based decision making
secondary gustatory cortex satiation response
response decreases during satiation period and then increased again when satiation went away
*reduced response when satiated
multimodal sensory integration with taste
taste-odor (reward based decision making)
taste-touch (texture of taste on tongue)
*taste, olfaction, sensory
what brain area responds when subject is thirsty
posterior insula`
what are the 3 functions of the olfactory system
identify food (pleasant smells), identify harmful smells/toxins, communicate via pheromones
what are the majority of the smells we detect
bad smells (~80% bad 20% good)
how do we let in chemical odors into our sensory system
sniffing through nasal passages to sample odorants
why is sniffing efficient for sampling odors
allows more rapid stimulus acquisition
where are olfactory receptor cells
in olfactory epithelium at the roof of the nasal cavity
how does size of olfactory epithelium impact sense of smell
larger surface area = higher olfactory acuity
anatomy of olfactory epithelium
cilia of olfactory receptor cells immersed in mucus layer; olfactory receptor cells form olfactory nerve
olfactory epithelium basal cells
supporting cells; source of new olfactory receptor cells (they are replacedc every 4-6 weeks)
cribriform plate
a thin, horizontal bone structure forming the roof of the nasal cavity; channels that allow axons access to higher levels of olfactory system
mechanism of depolarization for olfactory receptor cell
-odor molecules bind to odorant receptor protein
-G olf protein activated (g coupled protein receptor)
- adenylyl cyclase activates cAMP
Na+ and Ca2+ ion channels open and Cl- channels close
how does odor response change over time
response adapts in about one minute
how many genes code for olfactory receptor proteins in humans
350 (3-5% of genome)
how many odaratns can each unique receptor protein (coded by a specific receptor gene) bind to
a few different scents
how many receptor genes do most receptor cells express
1
how do you differentiate odorants since the olfactory receptor cells are broadly tuned
population coding
how many recruits proteins are expressed by each receptor cell
1
how do olfactory receptor cells code for odorant concentration
current flow of cilia and number of action potentials (to an extent until they plateau) increase with concentration
olfactory bulb
receive information about smells from olfactory receptor cells
glomeruli
circular clusters in the olfactory bulb that recive input from olfactory receptor cells
mitral cells
second order olfactory neurons that recive info from glomeruli and send it down olfactory tract
what process occurs in the olfactory bulb via the glomeruli
convergence
in each glomerulus, how many axons from receptor cells converge on dendrites of how many mitral cells
25,000 axons of receptor cells converge onto 100 second order mitral cells
organization of olfactory genes/proteins in glomeruli
each glomerulus receives input from olfactory receptor cells expressing a particular gene (have a particular receptor protein).
neural activation patterns in the bulb
different odorants activate different neural signals
spike rate/timing codes
information from both spike rate and spike timing codes give info about scents in the environment
how does the olfactory bulb recive info about odorant concentration
more glomeruli activated = higher conc of odorant
neural coding for odorant concentration
increase in concentration= increase in spike rate and spike timing codes
*short time between sniff and first action potential
why is the olfactory system the exception for the sensory systems (mechansim)
bypasses the thalamus
olfactory system mechanism
olfactory bulb, piriform cortex (primary olfactory cortex), orbitofrontal cortex (higher order processing)
evolutionary reason why olfaction does not go through thalamus
thalmus shuts off sensory input when sleeping but having smell could protect from harm/ predators
pathway by which olfactory bulb sends information
lateral olfactory tract
where can olfactory bulb send info to in the olfactory cortex
-primary olfactory cortex = pirifrom cortex -> OFC, insular cortex, laterna hypothalmus
-amagdala
-entrhorinal cortex, hippocampus
main target the olfactory bulb projects to
piriform cortex
