Deck 6: Olfaction, Taste, Audition, and Somatosensation

Question 1

Example of dendrodentritic synapses include all of the following except:
(a) granule cells and mitral cells.
(b) periglomerular cells and mitral cells.
(c) photoreceptor cells and bipolar cells.
(d) horizontal cells and bipolar cells.
(e) amacrine cells and bipolar cells.

Answer 1

(C)
Granule cells, periglomerular cells, horizontal cells, and amacrine cells both receive and transmit information via their dendrites. Photoreceptor cells and bipolar cells only form canonical excitatory axo-dendritic synapses.

Question 2

Which of the following statements is false?
(a) Each ORN innervates only one or two glomeruli in the olfactory bulb.
(b) Each mitral cell innervates only one or two glomeruli in the olfactory bulb.
(c) ORNs and mitral cells are excitatory.
(d) Periglomerular cells and granule cells are inhibitory.
(e) None of the above

Answer 2

(B)
Mitral cells have apical dendrites innervating a single glomerulus but also secondary dendrites that contact inhibitory granule cells, allowing lateral inhibition.

Question 3

Follow-up experiments to those in adult flies were performed in Drosophila larvae, which have even smaller and simpler olfactory systems. Which of the following reported observations was not consistent with conclusions derived from studies of the adult olfactory system?
(a) Each ORN expresses a single type of olfactory receptor.
(b) Each ORN axon typically innervates a single glomerulus in the antennal lobe.
(c) Each projection neuron's dendrites typically innervates a single glomerulus in the antennal lobe.
(d) Each projection neuron typically connects one specific glomerulus in the antennal lobe with one stereotyped substructure in the mushroom body dendritic field.
(e) Each intrinsic mushroom body neuron innervates several glomeruli in the mushroom body calyx, apparently randomly.

Answer 3

(D)
Larval studies revealed that PN axon arborization in the mushroom body was highly stereotyped, in contrast to predictions from axon tracing studies in the adult brain.

Question 4

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?

Question 5

Olfactory GPCR genes:
(a) include sequences encoding amino acids that are highly conserved in mammals.
(b) include sequences encoding amino acids that are highly variable between gene family members to permit binding to diverse odorants.
(c) probably underwent many duplications under selection pressure in rodents.
(d) accumulate more nonsense mutations in species that rely less heavily on smell.
(e) All of the above

Question 6

All sensory modalities are relayed to the cortex through the thalamus except for the:
(a) visual system.
(b) auditory system.
(c) somatosensory system.
(d) olfactory system.
(e) gustatory system.

Question 7

Odorant detection by a given olfactory receptor neuron could be monitored (at least in theory) by:
(a) an increase in internal cAMP.
(b) an increase in internal Ca²⁺.
(c) an increase in internal Na⁺.
(d) a decrease in internal Cl^-.
(e) All of the above

Question 8

Olfactory information has a discernable organization in all of the following structures except for the:
(a) olfactory bulb.
(b) piriform cortex.
(c) cortical amygdala.
(d) accessory olfactory bulb.
(e) None of the above

Question 9

Mechanisms for termination of olfactory responses in ORNs include:
(a) inhibition of the CNG channel by Ca²⁺/calmodulin.
(b) inhibition of the phosphodiesterase PDE1c by Ca²⁺/calmodulin.
(c) conversion of ATP to cAMP.
(d) activation of ACIII by CaMKII.
(e) All of the above

Question 10

It is very likely that humans use the main olfactory system for pheromone detection, given that:
(a) the TRPC2 gene has become a pseudogene in humans.
(b) the V2R genes have become pseudogenes in humans.
(c) the vomeronasal organ appears only transiently during human development.
(d) female humans' menstrual cycles can be influenced by compounds extracted from the armpits of donor females.
(e) All of the above

Question 11

How does the insect olfactory circuit resemble the vertebrate olfactory circuit?

Question 12

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:
(a) periglomerular cell.
(b) granule cell.
(c) mitral cell.
(d) ORN.
(e) amacrine cell.

Question 13

Each glomerulus in the mammalian olfactory bulb:
(a) receives information from the binding of a single type of odorant.
(b) receives information from the binding of a single type of olfactory receptor.
(c) is the site of convergence of the axons of ORNs expressing the same olfactory receptor.
(d) b and c
(e) a, b, and c

Question 14

Which spatial map in the brain does not correspond to spatial properties of the stimulus?
(a) Visual map in tectum/superior colliculus
(b) Primary somatosensory cortex
(c) Primary motor cortex
(d) Olfactory map in olfactory bulb
(e) Auditory map in inferior colliculus

Question 15

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

Question 16

ORNs expressing the same odorant receptor:
(a) are spatially clustered in the nasal epithelium.
(b) are distributed randomly within one of four zones in the nasal epithelium.
(c) are distributed randomly throughout the entire nasal epithelium.
(d) are distributed randomly throughout the olfactory bulb.
(e) None of the above

Question 17

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.

Question 18

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.

Question 19

In the third order insect brain structure called the lateral horn, olfactory inputs appear to be organized according to:
(a) similarity of chemical structure.
(b) spatial location in the external world.
(c) biological relevance (for example, food vs. reproduction).
(d) All of the above
(e) None of the above

Question 20

C. elegans avoid particular odors because these odorants:
(a) are inherently aversive chemicals.
(b) activate particular receptors that initiate a signal transduction cascade signifying aversion.
(c) activate particular receptors that are expressed by specific neurons that mediate avoidance.
(d) inhibit particular receptors that are expressed by specific neurons that mediate attraction.
(e) None of the above

Question 21

In both owls and mammals, interaural time and level differences permit sound localization via an auditory spatial map at the level of the:
(a) cochlear nuclei.
(b) nucleus laminaris/superior olivary nucleus.
(c) inferior colliculus.
(d) thalamus.
(e) primary auditory cortex.

Question 22

The overrepresentation of sound frequencies between 60 and 62 Hz in the Doppler-shifted constant frequency area of a bat's auditory cortex reflects the importance of echolocation for discrimination of the:
(a) size of an object.
(b) relative velocity of an object.
(c) distance of an object.
(d) biological significance of an object (prey vs. non-prey).
(e) None of the above

Question 23

Sound intensity is encoded by:
(a) the position of an activated hair cell along the basilar membrane of the cochlea.
(b) the firing rate of downstream spiral ganglion neurons.
(c) the position of the termination of a specific spiral ganglion neuron on the hair cell.
(d) a and b
(e) b and c

Question 24

All of the following are necessary for glutamate release by hair cells except:
(a) Ca²⁺ entry.
(b) K⁺ entry.
(c) a 2^nd messenger.
(d) a stretch-sensitive mechanotransduction channel.
(e) Ca²⁺-dependent cell adhesion molecules.

Question 25

The representation of sound frequency in a tonotopic map is established in the cochlea and maintained in the:
(a) superior olivary nucleus.
(b) inferior colliculus.
(c) thalamus.
(d) primary auditory cortex.
(e) All of the above

Question 26

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.

Question 27

Indicate whether each of the following statements is true of the vestibular system, the auditory system, both, or neither.
A. Depolarization of hair cells activates voltage-gated Ca²⁺ channels and glutamate release.
B. Ganglion neurons fire action potentials at a high rate in the absence of sensory stimuli.
C. Force exerted on stereocilia opens mechanotransduction channels in hair bundles.
D. Hair cells are tuned to different frequencies according to their location.
Somatosensation: How Do We Sense Body Movement, Touch, Temperature, and Pain?

Question 28

Opioids derived from the poppy, such as morphine:
(a) bind G-protein-coupled receptors that are responsive to endorphin and encephalin.
(b) act directly on peripheral sensory neurons.
(c) act directly on spinal cord neurons.
(d) act directly on neurons in the brainstem.
(e) All of the above

Question 29

The Asian small-clawed otter, which is closely related to omnivorous dogs and bears, has a nonfunctional T1R2 receptor gene. What does this information predict about the food preferences of this species?

Question 31

Which of the following statements is not true of both olfaction in C. elegans and taste in mammals?
(a) Each sensory neuron expresses multiple types of receptor.
(b) Sensory neuron activity reflects the biological significance of the odorant.
(c) A large number of chemical compounds can be discriminated from each other.
(d) All of the above
(e) None of the above

Question 32

The first stage at which auditory inputs are integrated with those of other sensory modalities is the:
(a) dorsal cochlear nucleus.
(b) superior olivary nucleus.
(c) inferior colliculus.
(d) thalamus.
(e) primary auditory cortex.

Question 33

Frequency selectivity of the inner hair cells is greatly enhanced by:
(a) force generated by the opening of the mechanotransduction channel in inner hair cells.
(b) force generated by the opening of the mechanotransduction channel in outer hair cells.
(c) myosin motors at the tips of the stereocilia.
(d) voltage-dependent changes in length of the outer hair cells.
(e) All of the above

Question 34

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.
Touch sensory neurons synapse with target projection neurons of the ___________ horn of the spinal cord in the ___________ dorsal column pathway and send a branch up to the ___________ in the ___________ dorsal column pathway. Medullary target neurons cross the midline before ascending to the ___________. In addition, touch information from ___________ skin is relayed by distinct dorsal horn projection neurons to the ___________ cervical nucleus via the ___________ tract pathway.
amygdala lateral
direct medial
dorsal medulla
glabrous spinocervical
hairy thalamus
indirect ventral

Question 35

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?

Question 36

Which of the following is not true of nociceptive neurons?
(a) Their axon fibers have the fastest conduction speeds among somatosensory neurons.
(b) They typically have free nerve endings.
(c) They can be activated by heat.
(d) They can be activated by mechanical stimuli.
(e) They can be activated by specific chemical compounds.

Question 37

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

Question 38

Sites of tissue damage or infection are more sensitive to heat because:
(a) there are no endogenous analgesics to inhibit nociceptive pathways.
(b) molecules produced by the inflammatory response also increase the sensitivity of TRP channels to sensory stimuli via a second messenger system.
(c) the neurons that modulate thermosensation are among the most easily injured or damaged.
(d) the enzymes that synthesize prostaglandin are temperature-sensitive.
(e) None of the above

Question 39

Activity in the sensory neurons that respond to a high concentration of salt in food:
(a) mediates attraction.
(b) can be inhibited by amiloride.
(c) responds only to sodium chloride.
(d) can also activate the bitter and sour tasting systems.
(e) All of the above

Question 40

Which of the following would be expected to activate neurons expressing the TRP channel family member TRPV1?

A) Temperatures < 26 $\degree$ C
B) Temperatures > 43 $\degree$ C
C) Capsaicin
D) a and b
E) b and c

Question 41

In monkeys trained to report detection of a vibratory stimulus, activity in which part of the cortex most accurately predicted a behavioral response signifying perception (Figure Q6-42)? Figure Q6-42
(a) Primary somatosensory cortex
(b) Secondary somatosensory cortex
(c) Premotor cortex
(d) Primary motor cortex
(e) None of the above

Question 42

Perceptual and electrophysiological experiments in humans and monkeys revealed that the threshold amplitude for perceptual detection of high-frequency repetitive mechanical stimuli:
(a) was significantly different between species.
(b) closely matched the lowest amplitude that activated Meissner corpuscles.
(c) closely matched the highest amplitude that activated Meissner corpuscles.
(d) closely matched the lowest amplitude that activated Pacinian corpuscles.
(e) closely matched the highest amplitude that activated Pacinian corpuscles.

Question 43

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??