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bisc307--exam_2_(sp._06)

bisc307--exam_2_(sp._06) - Exam 2 Answers BISC 307L General...

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Exam 2 Answers BISC 307L – General Physiology March 6, 2006 NOTE: The given answers for the subjective questions are not the only ones possible. Grading for each of the subjective questions is done relative to other students’ answers, by one TA who applied uniform criteria. 1. Which one of the following statements about sensory receptors is true ? (b) a. Tonic receptors are best suited for detecting changing stimuli, and phasic receptors are best suited for monitoring constant stimuli. b. Progressive activation of K + channels can cause adaptation in a sensory receptor. c. Spontaneous activity in sensory neurons diminishes overall sensitivity because it creates background noise in the system. d. For touch-sensitive neurons in the somatosensory system, only those whose mechanoreceptive terminals are located in the skin have receptive fields. e. Information from touch-sensitive neurons in lumbar dorsal root ganglia ascends to the brain via tracts located in the anterior and lateral regions of the spinal cord. 2. How does the existence of multiple parallel channels enhance sensitivity in sensory systems? Be sure to discuss the role of spatial summation in your answer. ANS: Parallel channels enhance sensitivity in the following way. A weak stimulus may have only a small chance of producing an action potential in any particular receptor. Since most receptors are spontaneously and randomly active, an “extra” action potential, correlated in time with the stimulus, would be an ambiguous signal. If the CNS monitors many parallel channels at once, however, several “extra” action potentials, occurring simultaneously and synchronously with the stimulus, would be a clear signal. The basic mechanism by which the CNS monitors multiple channels is by convergence of the parallel axons onto a single postsynaptic neuron. Simultaneously arriving action potentials result in simultaneous epsps that sum spatially to bring the postsynaptic neuron to threshold. 3. Which one of the following is not a typical response to sympathetic nerve activity? (e) a. increased heart rate d. increased respiratory rate b. dilation of bronchioles e. increased salivary secretion c. vasoconstriction in intestines f. increased alertness 4. Write one number in each blank, to best match each of the steps in skeletal muscle contraction (on the left) with its functional significance (on the right). _______ a. Ca 2+ pumping into SR 1. breaks the cross-bridge _______ b. binding of ATP to myosin 2. terminates cross-bridge cycling _______ c. release of P i 3. causes depolarization of transverse tubules _______ d. binding of Ca 2+ to troponin 4. causes rigor mortis 5. change in myosin conformation causing filaments to slide 6. forms the cross-bridge ANS: a-2, b-1, c-5, d-7 7. trigger that initiates cross-bridge cycling
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