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Problem Set 4: Mechanotransduction, Olfaction, and Vision 1) It turned out that an antibiotic furosemide selectively destroys outer hair cells in both cochleas. What would happen to the auditory processing? a. bilateral deafness b. decrease in sensitivity of ears to sound c. no change in sensitivity to pure tones but decreased sensitivity to speech d. increased sensitivity to some sounds 2) What is the principle function of the tympanic membrane and the ossicular chain of the middle ear? To transform air pressure waves hitting the tympanic membrane into fluid movement in the cochlea 3) What are the first cells in the auditory system to fire action potential? Spiral ganglion neurons 4) We learned that in visual processing information from the retina is relayed in the thalamus before it is sent to relevant cortical area. The corresponding thalamic relay of the auditory system is: a. the lateral geniculate nucleus b. the medial geniculate nucleus c. the inferior colliculus d. the superior colliculus 5) Inner hair cells a. are more numerous than outer hair cells b. provide more input to the auditory nerve than outer hair cells c. have a many-to-one ratio with spiral ganglion cells d. receive efferent input from the brain stem 6) The opening of K+ channels produces a ___________ in hair cells because of the __________ concentration of K+ in the endolymph and the _____________ hair cell membrane potential. a. hyperpolarization; low; positive b. depolarization; low; positive c. depolarization; high; negative d. depolarization; high; positive e. hyperpolarization; high; negative f. hyperpolarization; high; positive 7) The structure that forms the interface between the stapes and cochlea is the a. tympanic membrane b. basilar membrane c. round window d. oval window 8) The basilar membrane a. is wider at the base end than at the apex b. is stiffer at the apex than the base c. responds to low frequencies at the apex d. is inflexible 9) A difference between rods and cones is: a. Rods hyperpolarize to light, while cones depolarize to light b. Cones do not use the effector enzyme phosphodiesterase c. Cones and rods use different types of opsins d. Only cones contain retinal 10) One type of bipolar cells contains a special receptor, mGluR6, which is sign reversing (the cell hyperpolarizes when glutamate binds to this receptor). When the drug APB is applied to the retina, the response of the neurons containing this receptor is blocked. Which of the following results would you expect from the application of APB to the retina? a. OFF-bipolar cells will not respond to any stimulus b. Retinal ganglion cells in the fovea, but not in the periphery, will be affected c. V1 cells will no longer respond to the light edge of a bar drifting through their receptive fields d. ON-center retinal ganglion cells will respond exactly like OFF-center retinal ganglion cells This is not a very good question. (a),(b), and (d) are clearly wrong. (c) is half-wrong as shutting down the sign-reversing cells with APB means that the ON-center cells will be shut down. However, the V1 cells will still respond to bars due to the contribution of OFF-center cells, the response will just be reduced. 11) If a patient cannot see the left-most part of his left visual field (but can see in all other areas), he may have a lesion a. In the left optic nerve b. In the right optic nerve c. In the left optic tract d. In the right optic tract e. In the optic chiasm 12) The optic disk is a “blind spot”in the visual field because: This is where the retinal ganglion cell axons leave the retina and therefore there are no photoreceptors (and thus no response to light) at this location. 13) The fovea allows for increase visual acuity by which of the following specializations: a. high ratio of photoreceptors to ganglion cells b. lateral displacement of the ganglion cells from the retina c. all of the photoreceptors here are rods, which are more resistant to photobleaching d. the abundance of blood vessels to nourish this metabolically active area e. ALL are TRUE answers (a) and (b) are both correct 14) In comparison to other G-protein coupled second messenger signaling pathways (like metabotropic neurotransmitter receptors) the situation in photopigment transduction is different because: The receptor is activated by light instead of ligand (there are probably other acceptable answers for this question). 15) What is true about the distribution of rods and cones in the retina? Cones are concentrated in the fovea while rods are concentrated in the periphery. 16) What happens in a photoreceptor cell (a rod, for example) in response to a light stimulus? a. rod membrane depolarizes because Na+ channels open as a result of a decrease in second messenger cGMP b. rod membrane hyperpolarizes because K+ channels open as a result of a decrease in second messenger cGMP c. rod membrane hyperpolarizes because Na+ channels close as a result of a decrease in second messenger cGMP d. rod membrane depolarize because K+ channels close as a result of a increase in second messenger cGMP 17) If the parvocellular layers of LGN are bilaterally inactivated then we might expect Loss of high resolution vision, perception of form, and perception of color. Perception of motion would still be maintained. 18) If you inject radioactive proline into an eye what cells would you observe labeled in the contralateral LGN? a. cells in parvocellular layers of LGN (layer 3-6) b. cells in magnocellular layers of LGN (layers 1 and 2) c. cells in layers 1, 4 and 6 d. cells in layers 2,3 and 5 e. only koniocellular layers would be labeled 19) If you inject radioactive proline into one eye what cells would you observe labeled in layer 4 of V1? Ocular dominance columns 20) In what ways are simple and complex cells in the primary visual cortex different? a. both simple and complex cells are orientation selective but have different receptive field structure b. simple cells are orientation selective whereas complex cells are not c. simple cells are selective for vertical and horizontal orientations whereas complex cells are selective for all orientations d. simple cells receive input from magnocellular layers of LGN whereas complex cells receive input from parvocellular layers of LGN 21) The concept of the receptive field depends on the fact that: a. At each level of processing of a visual stimulus, all synaptically connected neurons in a given visual circuit have identical receptive field properties b. Visual information is processed in parallel circuits c. Visual information is organized into retinotopic maps d. Each neuron in the visual pathway responds to stimulation of the retina with a characteristic change in membrane potential This is not a very good question. Answer (a) is incorrect and (b) is irrelevant. Answer (d) is probably the best answer, but (c) could be argued for as well. 22) In the olfactory system: a. primary olfactory receptor neurons have axons that project directly to the brain, where they makes synapses onto neurons of the olfactory bulb. b. olfactory stimuli depolarize primary olfactory receptor neurons by means of G-protein-coupled receptor molecules located in the cilia of the receptor neurons. c. each glomerulus in the olfactory bulb receives synaptic inputs from the primary olfactory receptor neurons of one particular type, among the thousand or so different types of receptor cell found in the olfactory epithelium. d. all of the above e. none of the above. 23) What causes olfactory receptor neurons to depolarize? Odorant binds to G-protein coupled receptor => G activates adenylyl cyclase => Adenylyl cyclase produces cAMP from ATP => cAMP opens cyclic nucleotide-gated channels => influx of Na+ (and Ca2+) through channels depolarizes cell.