Neurophysiology Exam Questions: BME 502 (2001), Exams of Biology

Download Neurophysiology Exam Questions: BME 502 (2001) and more Exams Biology in PDF only on Docsity! BME 502 Name: _______________________ Exam #2 (2001) Question #1 TOTAL TIME: 2 HRS 1. The repolarization of the action potential is brought about by the a) very small increase in the intracellular Na+ concentration caused by excitation. b) potassium efflux, which sets in with a time lag after depolarization. c) termination of the sodium influx during excitation. d) expulsion of the Na+ influx by the sodium pump. Answer: b) or b) c) 2. At the peak of action potential the membrane potential becomes postitive because: a) The Na+ concentration in the cell becomes larger than the K+ concentration. b) A Na+ influx generates a slight excess of positive charges on the inside of the membrane. c) The membrane potential becomes more positive than the Na+ equilibrium potential. d) The membrane potential approaches the Na+ equilibrium potential. Answer: b) d) 3. Which of the following factors reduces the velocity of conducion of a nerve? a) Reduction in fiber diameter. b) Loss of the myelin sheath (in the event of degeneration) c) Increase in the extracellular Na+ concentration. d) 50% reduction in the extracellular K+ concentration. Answer: a) b) 4. Which of the following statements is true? a) Hyperpolarization, sometimes, can also generate action potential. b) Very slow depolarization might NOT generate action potential. c) Action potential, when initialed in the middle of axon, would propagate bi-directionally. d) The inactivation is both voltage-dependent and time-dependent. Answer: a) b) c) d) BME 502 Name: _______________________ Exam #2 (2001) Question #2 (cont) (c) why did the amplitude of the early inward current reach its peak at approx 2 msec when Vc was -30 mV and yet take only approx 1 msec to reach its peak when Vc was 0 mV? because the rate of activation of voltage-dependent Na currents is voltage-dependent, so the large step will activate channels faster (d) why did the peak of the early inward current decrease when Vc was varied from 0 mV to +40 mV? because approaching equilibrium potential for Na, so driving force is decreased (e) estimate the threshold membrane potential; justify your answer approx -20 mV to -10 mV BME 502 Name: _______________________ Exam #2 (2001) Question #2 (cont) (f) if the inward current is carried by a single species of positively charged ion, X+, estimate the equilibrium potential for X+ and explain your answer +60 mV; early inward current reverses to an outward current (g) if the late outward current is carried by K+ ions and EK can be assumed to be approximately 75 mV, why is there no reversal of the late outward current when Vc is below 75 mV? K channels are voltage-dependent and do not open below -75 mV BME 502 Name: _______________________ Exam #2 (2001) Question #3 The intracellular recordings shown in the figure below were obtained from three different brain regions and illustrate the diversity of action potential responses that neurons can exhibit in response to a depolarizaing current injection. (a) What two currents are most likely to underlie the progressively longer inter-spike intervals seen in the response in panel A? Provide a clear rationale for each choice and explain how they both are needed to account for the phenomenon voltage-dependent Ca currents (specifically, L-type, which require large and long-lasting depolarization), and Ca-activated K currents (specifically, the slow AHP), which have slow kinetics, require increases in intracellular Ca concentration, and act to slowly hyperpolarize the membrane, eventually preventing action potential firing to depolarization