L9: The Chemical Senses: Olfaction & Taste

Question 1

Where do you find most of the olfactory cells?

Answer 1

cell bodies of these cells are located in the olfactory epithelium below cribiform plate

Question 2

Neurons in olfactory epithelium relay info via axonal projections thru Cribiform plate, which will relay it to the olfactory bulb. What are 2 impt functions of the cribiform plate?

Answer 2

large % of CSF drains out of here

• impt for CSF homeostasis
• conduit for spread of infection to CNS

Question 3

The olfactory bulb is the 1st relay in the olfactory sensory chain. From here, info can flow anywhere, such as (list 4)

Answer 3

pyriform cortex
olfactory tubercle
amygdala
entorhinal cortex

Question 4

Olfactory epithelium contains which 3 cells?

Answer 4

1 - bipolar neuron cells that contain thin unmyelinated axons that project to bulb (1000 different types of olfactory sensory neurons that look at world in a slightly diff way)
2 - basal cells provide cell renewal & regeneration
3 - supporting cells

Question 5

Olfactory sensory neurons have a life span of 30 days. What cells help replenish these cell types?

Answer 5

basal cells continually undergo mitotic divisions to make new basal cells and/or neurons.

Question 6

Briefly describe the signal transduction pathway that occurs in olfactory neurons when odorant is delivered to epithelium.

Answer 6

1 - odorant delivered to epithelium
2 - odorant diffuses thru mucus to reach cilia
3 - odorant interacts w/ receptor protein
4 - binding to g-protein coupled receptor = depolarization
5 - increase cAMP –> binds to ion channel opening it & depolarizing cell (Ca2+ dependent)

Question 7

What type of receptors are olfactory receptors to which odorants bind?

Answer 7

Olfactory receptors are the largest family of g-protein receptors. All of the receptors have a common tertiary structure w/ 7 transmembrane domains and a.a. sequence homology.

Question 8

Zonal distribution pattern is used to explain the olfactory system. What does it mean?

Answer 8

it has to do with the fact that neurons expressing a particular olfactory sensory receptors reside in very specific zones

within a zone, neurons expressing a particular olfactory receptor can be either homogenously distributed or have a clustered distribution pattern

Question 9

What does it mean to describe olfactory sensory neurons as promiscuous?

Answer 9

the particular olfactory receptor a neuron expresses determines the physiological responsiveness of that neuron. Any one olfactory receptor is tuned to respond to A LOT OF DIFFERENT odorants, which share a common molecular feature.

Question 10

Explain the structure of the olfactory bulb and list the 4 layers

Answer 10

Shaped like an onion with different layers

• glomerular layer
• external plexiform layer
• mitral cell layer
• granule cell layer

Question 11

What are mitral and tufted cells?

Answer 11

They are found in the olfactory bulb that serve as relay neurons that project to olfactory cortex.

Question 12

What are periglomerulur and granule cells?

Answer 12

They are in the olfactory bulb that serve as inhibitory interneurons that modulate activity of mitral and tufted cells

Question 13

Define glomerulus (neuropils) in terms of the olfactory bulb

Answer 13

it is the unit of anatomical and physiologic organization in olfactory bulb

Question 14

At the level of the olfactory epithelium, how are the odorants encoded?

Answer 14

spatially b/c there are inherent differences btw areas of epithelium in their responses to odorants

Question 15

Unlike other sensory systems, the projection of the olfactory epithelium onto the olfactory bulb is not point-to-point. They are?

Answer 15

quadrant-to-quadrant which are defined by the boundaries of the olfactory receptor expression zones. Within a quadrant, the axonal projections bring together the axon terminals of all “like-neurons” (so all of the neurons expressing a particular OR converge onto the same set of glomerulu)

Question 16

Explain the rule: one OR, one glomerulus

Answer 16

Olfactory neurons are broadly tuned and that all the neurons that express a single OR synapse together in a single glomerulus.

Question 17

Explain how the olfactory system all comes together in 3 steps

Answer 17

1) olfactory neurons with different receptors respond to odorants; there’s lateral inhibition that will weed out unnecessary stimulus (only high stimulus will stimulate the receptors)
2) different glomeruli are then activated by different odorants
3) each olfactory receptor looks at different parts of the odorants (ODOTOPE); NOT AT THE WHOLE MOLECULE (e.g. no such thing as a banana receptor)
* *odors would be identified and discriminated by the overall activation of glomeruli across the whole bulb

Question 18

list the 5 primary taste qualities

Answer 18

salt, sweet, umami, bitter, sour

Question 19

Where do taste buds get their innervation?

Answer 19

anterior 2/3 = CN VII -chorda tympani
posterior 1/3 = CNIX
epiglottis = CNX

each axon innervates from 2-10 taste cells

Question 20

The gustatory axons (carrying taste bud info) from tongue and epiglottis to the nucleus of solitary tract. The NTS has projections to _____,_______, _____, and they project to the ______, and -_____.

Answer 20

The NTS has projections to the VPM, hypothalamus and amygdala, which project to the insula and frontal cortex.

Question 21

There are four primary taste fields. List them and do they respond to all tastants?

Answer 21

• circumvallate papillae (posterior tongue) -BITTER
• foliate papilla (mid-lateral tongue) -SOUR
• fungiform papillae (anterior tongue) -SWEET/UMAMI/SALTY
• taste buds on the soft palate = SWEET

All of the taste fields respond to all tastants but each taste field is most sensitive to a particular taste quality.

Question 22

How are taste buds organized?

Answer 22

They are limited to specialized protrusions called papillae. Taste buds are pear-shaped collections of cells surrounded by basal lamina that are embedded in a SSE.

Question 23

Each taste bud contains how many cells and what type of cells?

Answer 23

Each taste bud has 50-100 cells that include receptor cells and basal cells.

Question 24

What happens when salt activates taste buds?

Answer 24

Salt stimuli are transduced via amiloride-sensitive Na+ channels (an ionic transduction mechanism), which results in an intracellular increase in calcium and transmitter release.

Question 25

What happens when there’s a sour stimulus?

Answer 25

Sour stimuli will open H+-sensitive cation channel, which will result in an intracelllular increase in calcium and transmitter release

Question 26

While salt and sour stimuli are transduced via ionic transduction mechanisms, how are sweet, bitter and umami stimuli transduced?

Answer 26

transduced thru a G-protein coupled mechanism, causing as increase in cAMP stimulating Ca2+ channels,

Question 27

Indicate which type of transduction mechanism is activated in these 5 different taste (sweet, bitter, umami, salt and sour) stimuli

Answer 27

sweet, butter, umami: g-protein coupled mechanism increasing cAMP will stimulate Ca2+ channel via IP3

salt: amiloride-sensitive Na+ channel

Acids: H+ sensitive cation channel

Question 28

Explain taste coding

Answer 28

single axons respond to many different primary stimulus qualities although they will have a preferential maximal response to only one

For instance, if you look at the # of axons from the chorda tympani nerve responding to sucrose, NaCl, HCl, they will have different responses, indicating that axons respond to many different primary stimulus.

Question 29

What is labeled line taste coding?

Answer 29

when you can rescue or delete the perception of one taste quality without impacting the others.

Question 30

Which cranial nerve system conveys oral irritation?

Answer 30

Trigeminal System

Question 31

T/f: Olfactory bulb glomeruli have the property such that they gather info from olfactory receptor cells that express a single odorants type

Answer 31

True

Question 32

Which of the following is not a part of the taste pathways?

A. Amygdala

B. VPM of thalamus

C. Hypothalamus

D. Frontal Cortex

E. Cerebellum

Answer 32

E. Cerebellum

Question 33

Which of the following is false about olfactory receptors?

A. They are G-protein coupled

B. 7 transmembrane domains

C. Each neuron expresses only one type

D. Narrowly tuned to specific odorants

E. None of the above

Answer 33

D.

Question 34

Signal transduction in olfactory neurons includes:

A. increase cAMP via G protein activation

B. depolarizing of the cells occurs via opening of Ca2+ channel

C. any particular olfactory neuron expresses one Odorant Receptor (OR) type.

D. any specific type of OR is clustered to a particular zone
E. all of the above

Answer 34

E