2008 Exam 2 Answers for Posting

2008 Exam 2 Answers for Posting - Exam 2 Answer - 2008 BISC...

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Exam 2 Answer - 2008 BISC 307L - General Physiology 16 Qs, total 94 pts. 1. Which one of the following statements about touch receptors in the skin of the hand is false? (c) a. The cell bodies of these sensory neurons are located in the dorsal root ganglion. b. Axons of these sensory neurons ascend to the brain in the dorsal columns of the spinal cord. c. Touch receptors in the skin of the hand are tonic receptors. d. Activity from these receptors passes through the thalamus on the way to the primary somatosensory cortex. e. These touch receptors have myelinated axons. 2. Almost all sensory receptors show adaptation to one extent or another. Name two (only 2) of the possible mechanisms for sensory adaptation, and briefly describe how each mechanism operates to cause adaptation. (Note: if you give more than 2 mechanisms, only the first 2 will be graded.) ANS: There are several possibilities, of which 4 were covered in class. These are: 1. Na+ channel inactivation: Stimulation depolarizes most sensory receptors, and depolarization both activates and, with a delay, inactivates Na channels. Sustained depolarization from a sustained stimulus converts most Na channels to the inactivated state, in which they cannot generate action potentials. 2. Ca2+ channel inactivation: As for #1, sustained depolarization from a sustained stimulus can inactivate Ca channels, although the mechanisms are different than for Na channels. In the inactivated state, inactivated Ca channels cannot carry regenerative inward currents to produce action potentials, nor can they let Ca2+ enter the cell to trigger transmitter release. 3. K+ channel activation: Several types of K+ channels would be opened by sustained depolarization from a sustained stimulus. The resulting increase in K+ permeability would render the sensory receptor less excitable by various ionic mechanisms. 4. Rearrangement of accessory tissues: For some sensory receptors, accessory tissues act as a filter between the applied stimulus energy and actual stimulation of the receptor itself. When the stimulus is initially applied, it is transmitted directly to the receptor which generates a response. With sustained application of the stimulus, rearrangements of the accessory tissue diminish the stimulus energy impinging on the receptor, so the response lessens. 3. With no more than a few words each, describe the general effect of parasympathetic stimulation on the following. ANS: a-decrease, b-decrease, c-increase, d-increase a. the size of the pupil of the eye b. diameter of the airways (bronchioles) in the lung c. secretion of saliva in the mouth d. blood flow to the genital organs 4. Cocaine blocks the reuptake of norepinephrine into presynaptic terminals. Briefly explain how this can cause a dangerous rise in heart rate and blood pressure. ANS: Reuptake of norepinephrine into the presynaptic terminals of postganglionic sympathetic
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2008 Exam 2 Answers for Posting - Exam 2 Answer - 2008 BISC...

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