Flashcards in L9: The Chemical Senses: Olfaction & Taste Deck (34):
Where do you find most of the olfactory cells?
cell bodies of these cells are located in the olfactory epithelium below cribiform plate
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?
large % of CSF drains out of here
-impt for CSF homeostasis
-conduit for spread of infection to CNS
The olfactory bulb is the 1st relay in the olfactory sensory chain. From here, info can flow anywhere, such as (list 4)
Olfactory epithelium contains which 3 cells?
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
Olfactory sensory neurons have a life span of 30 days. What cells help replenish these cell types?
basal cells continually undergo mitotic divisions to make new basal cells and/or neurons.
Briefly describe the signal transduction pathway that occurs in olfactory neurons when odorant is delivered to epithelium.
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)
What type of receptors are olfactory receptors to which odorants bind?
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.
Zonal distribution pattern is used to explain the olfactory system. What does it mean?
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
What does it mean to describe olfactory sensory neurons as promiscuous?
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.
Explain the structure of the olfactory bulb and list the 4 layers
Shaped like an onion with different layers
-external plexiform layer
-mitral cell layer
-granule cell layer
What are mitral and tufted cells?
They are found in the olfactory bulb that serve as relay neurons that project to olfactory cortex.
What are periglomerulur and granule cells?
They are in the olfactory bulb that serve as inhibitory interneurons that modulate activity of mitral and tufted cells
Define glomerulus (neuropils) in terms of the olfactory bulb
it is the unit of anatomical and physiologic organization in olfactory bulb
At the level of the olfactory epithelium, how are the odorants encoded?
spatially b/c there are inherent differences btw areas of epithelium in their responses to odorants
Unlike other sensory systems, the projection of the olfactory epithelium onto the olfactory bulb is not point-to-point. They are?
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)
Explain the rule: one OR, one glomerulus
Olfactory neurons are broadly tuned and that all the neurons that express a single OR synapse together in a single glomerulus.
Explain how the olfactory system all comes together in 3 steps
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
list the 5 primary taste qualities
salt, sweet, umami, bitter, sour
Where do taste buds get their innervation?
anterior 2/3 = CN VII -chorda tympani
posterior 1/3 = CNIX
epiglottis = CNX
each axon innervates from 2-10 taste cells
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 -_____.
The NTS has projections to the VPM, hypothalamus and amygdala, which project to the insula and frontal cortex.
There are four primary taste fields. List them and do they respond to all tastants?
-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.
How are taste buds organized?
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.
Each taste bud contains how many cells and what type of cells?
Each taste bud has 50-100 cells that include receptor cells and basal cells.
What happens when salt activates taste buds?
Salt stimuli are transduced via amiloride-sensitive Na+ channels (an ionic transduction mechanism), which results in an intracellular increase in calcium and transmitter release.
What happens when there's a sour stimulus?
Sour stimuli will open H+-sensitive cation channel, which will result in an intracelllular increase in calcium and transmitter release
While salt and sour stimuli are transduced via ionic transduction mechanisms, how are sweet, bitter and umami stimuli transduced?
transduced thru a G-protein coupled mechanism, causing as increase in cAMP stimulating Ca2+ channels,
Indicate which type of transduction mechanism is activated in these 5 different taste (sweet, bitter, umami, salt and sour) stimuli
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
Explain taste coding
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.
What is labeled line taste coding?
when you can rescue or delete the perception of one taste quality without impacting the others.
Which cranial nerve system conveys oral irritation?
T/f: Olfactory bulb glomeruli have the property such that they gather info from olfactory receptor cells that express a single odorants type
Which of the following is not a part of the taste pathways?
B. VPM of thalamus
D. Frontal Cortex
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