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Exam 6: Olfaction, Taste, Audition, and Somatosensation

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Question 1

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Which of the following is not true of the transformation of odorant coding between ORNs and projection neurons in the fly?

A) In each glomerulus, a small number of ORNs form synapses with a large number of target PNs.
B) PNs projecting to the same glomerulus form electrical synapses with each other to synchronize their activity.
C) The synapses between ORNs and PNs exhibit short-term depression, leading to circuit-level olfactory adaptation.
D) Local interneurons mediate presynaptic inhibition of ORN neurotransmitter release, leading to circuit-level olfactory adaptation.
E) Population-level PN responses permit higher discriminatory power than population-level ORN responses.

F) A) and B)
G) A) and C)

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Question 2

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If an experimenter were to express light-activated channelrhodopsin in a mouse using the Bhlhb5 promoter, what behavioral outcome would support the current model for responses to itchy vs. painful stimuli? (See Figure Q6-37.) Figure Q6-37

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In the current model, Bhlhb5⁺ neurons inh...

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Question 3

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In the visual system, horizontal cells are excited by photoreceptor cells and in turn inhibit both the photoreceptor cells that excited them and nearby bipolar cells. The olfactory equivalent of the horizontal cell is the:

Several experiments suggest that the binding of carbon dioxide to its specific receptor, Gr21a, in a particular subset of ORNs is sufficient to mediate avoidance behavior in flies, much like activation of the AWB neurons in C. elegans. Briefly describe a novel experiment to confirm that activation of Gr21a-expressing neurons is sufficient for odorant avoidance in flies.

Mechanisms for termination of olfactory responses in ORNs include:

Mammalian gustatory systems have evolved to avoid even trace amounts of a wide variety of toxic alkaloids. What key features of our taste systems underlie this adaptive sensitivity?

What experiments support a model in which mammalian olfactory GPCRs are expressed specifically in ORNs that project to a particular glomerulus in the olfactory bulb?

In insects, gustatory sensory neurons project from the proboscis and other structures to the subesophageal ganglion. Interestingly, insects have gustatory sensory neurons that mediate the recognition of water, which is necessary for animals to maintain osmotic homeostasis. Kristin Scott and colleagues have proposed that ppk28, a member of the Degenerin/Epithelial Sodium Channel family, is an osmosensitive ion channel involved in the cellular and behavioral response to water. A. ppk28 is a predicted ion channel recovered from a microarray screen for genes expressed in the proboscis of wild-type flies but not Poxn^-/- flies (which lack all taste neurons). How could you confirm experimentally that this gene was expressed in gustatory neurons? B. The experimenters found that about two-thirds of ppk28-expressing neurons were also positive for a marker of water-sensing neurons in taste bristles. Expression of a genetically encoded calcium sensor in ppk28⁺ neurons using the GAL4/UAS system allows visual monitoring of depolarization. What response would you predict from these neurons upon the presentation of aqueous solutions of various concentrations? C. How would you demonstrate that ppk28 was necessary for a cellular vs. behavioral response to water??

Example of dendrodentritic synapses include all of the following except:

Which of the following is not true of nociceptive neurons?

Sound intensity is encoded by:

Indicate whether each of the following statements is true of insects, vertebrates, both, or neither. A. Piezo is a mechanosensitive ion channel. B. Piezo is an innocuous touch sensor. C. An ENaC channel is an innocuous touch sensor. D. A TRP channel is an innocuous touch sensor.

All of the following are necessary for glutamate release by hair cells except:

Olfactory information has a discernable organization in all of the following structures except for the:

Fill in each of the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. The C. elegans AWC olfactory circuit has much in common with vertebrate rod and cone circuits. Light _____________ cones, inhibiting _____________ release. OFF bipolar cells with _____________ glutamate receptors are hyperpolarized, while ON bipolar cells with _____________ glutamate receptors are depolarized. Similarly, odorant binding _____________ AWC, inhibiting glutamate release. AIB expresses a(n) _____________ glutamate receptor and is hyperpolarized. AIY expresses a glutamate-gated _____________ channel and is depolarized. In both cases, parallel pathways serve to enhance contrast between the presence and absence of the stimulus. acetylcholine hyperpolarizes calcium ionotropic chloride mechanosensitive depolarizes metabotropic glutamate sodium

Activity in the sensory neurons that respond to a high concentration of salt in food:

In both owls and mammals, interaural time and level differences permit sound localization via an auditory spatial map at the level of the:

Olfactory GPCR genes:

The representation of sound frequency in a tonotopic map is established in the cochlea and maintained in the:

Piezo1 and Piezo2 were identified in an RNAi knockdown screen in a mouse neuroblastoma cell line. State whether each of the following experiments suggested that at least one Piezo was necessary, sufficient, or present in the right time and place to mediate touch mechanotransduction in vivo.