The chemical senses ( olfaction and taste)

Question 1

when you get a severe cold why do we PERCEIVE that food doesn’t taste as good?

Answer 1

because olfaction component of flavor is 1/3 of the flavor perception

Question 2

why are olfaction and taste problems important to identify in a pt?

Answer 2

b/c they can indicate more general disease ( serious) states.

Question 3

what is special about the sensory capacity of gustatory (taste) and olfactory receptors?

Answer 3

they can maintain sensory capacity despite death of old receptor elements and recruitment of new elements ( new olfactory neurons and new taste receptor cells respectively).

Question 4

Where does a large % of CSF flow out of in the olfaction/gustatory system and what is the implication of this?

Answer 4

the cribiform plate and this is a problem because it serves as a conduit for viruses to get into the nervous system.

Question 5

where are the olfactory cell bodies located?

Answer 5

in the olfactory epithelium lining below the cribiform plate

Question 6

where do the axons of the olfactory system travel to relay info?

Answer 6

via the axonal projections through the cribiform plate to the olfactory bulb

Question 7

what are the 4 olfactory bulb targets?

Answer 7

pyriform cortex ( olfactory cortex), olfactory tubercle, amygdala, entorhinal cortex

Question 8

from the amygdala where in the brain does the olfactory neuron travel?

Answer 8

orbitofrontal cortex ( emotional association),thalamus and hypothalamus

Question 9

from the entorhinal cortexwhere in the brain does the olfactory neuron travel?

Answer 9

hippocampal formation ( memory association)

Question 10

what capacity do olfactory epithelial basal cells have ?

Answer 10

they can replenish epithelium as mature sensory neurons die

Question 11

what is anosmic?

Answer 11

can’t smell

Question 12

what is parosmia

Answer 12

a change in the perception so that something doesn’t smell the way it usually does ( this can happen after exposure to extreme toxins b/c the neurons die and regenerate but regenerate incorrectly.)

Question 13

How long do sensory neruons last?

Answer 13

30 days

Question 14

what is the largest g protein coupled system in the body?

Answer 14

olfaction

Question 15

when an odorant interacts with a receptor protein what happens?

Answer 15

depolarization of the receptor potential occurs and cAMP increases via activation od adenly cyclase , cAMP binds an ion channel and opens it depolarizing the cell and letting Ca2+ in .

Ca2+ leads to Cl- channel opening which gives the olfactory signal a boost.

Question 16

how many olfactory receptors do we have?

Answer 16

1000s

Question 17

explain the specificity of odor receptors

Answer 17

they have some specificity but are promiscuous, i.e. compounds with similar chemical structure may use similar or same receptors.

There isn’t an orange or a rose receptor.

Question 18

what is the structure of the olfactory receptor?

Answer 18

a 7 transmembrane domain. all receptors have amino acid sequence homology.

Question 19

what is the distribution of the olfactory receptors?

Answer 19

they are split up into quarters with 1/4 residing in each zone.

Question 20

How many olfactory receptor types does a neuron express?

Answer 20

only one

Question 21

How are neurons expressing a particular olfactory receptor distributed?

Answer 21

homogenously or they can have a clustered distribution pattern

Question 22

How does the number of Odor receptors correlate to the number of odorants?

Answer 22

one odor receptor can respond to a lot of different odorants which share a common molecular feature.

Question 23

how do olfactory neurons encode information?

Answer 23

by virtue of spatial pattern

Question 24

where do similar patterns of olfactory receptors coalesce?

Answer 24

in the glomeruli of the bulb below the cribiform plate

Question 25

what do the mitral and tufted cells in the bulb do?

Answer 25

they are relay neurons that project to the olfactory cortex

Question 26

what are periglomerular cells and granule cells?

Answer 26

they are inhibitory interneurons that modulate activity of the mitral tufted cells.

Question 27

what is the outermost shell of the olfactory neuron?

Answer 27

the periglomerular cells

Question 28

all neurons expressing a particular olfactory receptor______________

Answer 28

converge onto the same set of glomeruli

Question 29

what happens to people who have specific anosmias?

Answer 29

they can’t discriminate between certain smells

Question 30

what is an odotope?

Answer 30

a single chemical moiety that Olfactory receptors recognize ( e.g. a phenyl group)

Question 31

what is the unit for recognizing a particular odotpe?

Answer 31

1 glomeruli

Question 32

what is the lateral inhibitory mechanism in the olfactory system?

Answer 32

it is the mechanism by which only maximally stimulated sensory neurons ( e.g. an 8 carbon structure) is pass “information” (smell in this case) along, where as incidentally stimulated sensory neurons ( e.g.. given above e.g. 5,6,7,9, and 10 carbon structures) ( activated due to a high stimulus) are filtered out by the granule cells at the level of the mitral and tufted cells so that only the maximally stimulated substance is perceived.

Question 33

what are the 5 tastes qualities?

Answer 33

salty, sweet, bitter, sour, and savory ( umami)

Question 34

which cranial nerves innervate the taste buds?

Answer 34

VII facial via the chord tympani to tongue and the greater petrosal to the palate ( anterior 2/3 tongue)

and glossopharyngeal ( posterior 1/3 tongue), and vagus ( epiglottis)

Question 35

how many taste cells does each axon innervate?

Answer 35

2-10 taste cells

Question 36

what do gustatory axons innervate?

Answer 36

the nucleus tractus solitarius

Question 37

after the information from the neurons for taste travel tothe NTS in the brain, where does it go?

Answer 37

to the ventral posterior medial (VPM) nucleus of the thalamus and from there to the hypothalamus, and amygdala.

Question 38

what are the taste buds of the soft palate , circumvallate, foliate and fungiform papillae, most sensitive to?

Answer 38

sweet

Question 39

where is sweet and savory ( umami) most sensitive?

Answer 39

the anterior portion of the tongue

Question 40

where is salty most sensitive?

Answer 40

the anterior perimeter of the tongue

Question 41

where is sour most sensitive?

Answer 41

the lateral tongue

Question 42

where is bitter most sensitive?

Answer 42

the posterior of the tongue

Question 43

where are the taste buds located?

Answer 43

in specialized protrusions called papillae

Question 44

Describe taste receptors

Answer 44

they are taste receptor cells not neurons and they last 10 days after which the basal cells replenish them ( self renewal)

Question 45

which 2 tastes are transduced through ionic transduction which results in an increase in calcium and transmitter release?

Answer 45

salt ( Amiloride -sensitive sodium channel) and sour (H+ -sensitive channel)

Question 46

What tastes are transducer via second messenger ?

Answer 46

bitter,sweet and umami.

increase in cAMP–> stimulation of a TRPM5 Ca2+ channel via IP3

Question 47

What is the heterodimer in the second messenger sys for sweet?

Answer 47

T1R2 and T1R3

Question 48

What is the heterodimer in the second messenger sys for umami?

Answer 48

T1R3 and T1R1

Question 49

What is the homodimer n the second messenger sys for bitter?

Answer 49

T2R

Question 50

How does the trigeminal nerve contribute to taste/

Answer 50

it contributes pungency ( irritation ), which is activated by capcacin in spicy food for e.g..
this must be distinguished from odor and taste

Question 51

what does the labeled line taste coding demonstrate?

Answer 51

that if you remove a homo or heterodimer and remove phospholipase C which is in all taste cellsand then replace them both you will get only the one with the homo/heterodimer removed and the rest will not be restored.