bisc307_exam_2_(sp._05,_herrera)

bisc307_exam_2_(sp._05,_herrera) - EXAM 2 POSTED ANSWER KEY...

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EXAM 2 – POSTED ANSWER KEY 1 1. Briefly describe how a tonic mechanoreceptor in the skin can signal the intensity of a touch stimulus. ANS: Tonic touch receptors signal stimulus intensity by the frequency of firing of action potentials during the time the stimulus is applied. 2. How, in general, does averaging across multiple parallel channels increase the ability of sensory systems to detect weak stimuli? Be sure to include the role of spontaneous activity in your answer. ANS: Typically, sensory neurons are spontaneously active, even in the absence of a stimulus. A weak stimulus would cause only a slight increase in the probability of an action potential occurring in a single channel. For a single channel, this would be an ambiguous signal because the extra action potential would be difficult to detect on the background of spontaneous activity. Also, spontaneous action potentials in different channels occur asynchronously, such that only rarely do action potentials in different channels occur at the same time. Therefore, the simultaneous occurrence of even a single action potential in several parallel channels constitutes an unambiguous signal that a weak stimulus has occurred. 3. Which one of the following statements is true? a. Peptide transmitters are synthesized in the axon terminals of the neurons that release them. b. Acetylcholine is the main neurotransmitter released by sympathetic postganglionic neurons. c. Parasympathetic preganglionic axons leave the CNS in the thoracic and lumbar regions. d. The cell bodies of parasympathetic postganglionic neurons are located near their target cells. -ANSWER e. The parasympathetic innervation of the face passes through the superior cervical ganglia. 4. Stimulation of the _____________________________________ nerves to the heart would slow the rate of heart beating, while stimulation of the _______________________________ nerves to the heart would increase the rate of heart beating. ANS: parasympathetic / sympathetic 5. Indicate whether each of the following statements is true (T) or false (F) by writing the appropriate letter in the blank. ______ a. Dihydropyridine receptors are voltage sensors in the transverse tubule membrane. (T) ______ b. Type I skeletal muscle fibers contain large numbers of mitochondria. (T) ______ c. When a muscle fiber undergoes an isotonic contraction, the spacing between z-disks remains constant. (F) ______ d. Skeletal muscle fibers with more Ca
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bisc307_exam_2_(sp._05,_herrera) - EXAM 2 POSTED ANSWER KEY...

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