151_Final_2007

151_Final_2007 - MCDB 151/251 Name Final Exam Fall 2007 200...

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MCDB 151/251 Name ___________________________________________ 1 Final Exam Fall 2007. 200 pts total Part I. Ion Channels & Action Potentials (40 pts) 1) Describe and compare the mechanisms of action potential propagation in a myelinated axon and in an unmyelinated axon with respect to the following: a) (1 pt) relative speed of action potential conduction: b) (3 pts) location of ion channels: c) (6 pts) how an action potential is transmitted along the axon: 2) (4 pts) At the level of ion channels, list 2 reasons for the refractory period. i) ii)
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MCDB 151/251 Name ___________________________________________ 2 3) (3 pts) A neuron with voltage-activated Na and K channels is voltage clamped and the currents recorded for a test pulse to 0 mV. For this neuron, E K = -80 mV and E Na = + 50 mV. Draw the currents below that you expect to see. 4) (3 pts) You now add tetrodotoxin to the same neuron, and again record the currents for a voltage pulse to 0 mV. Draw the currents below that you expect to see. 5) (5 pts) You are interested in predicting the current through potassium channels in a neuron at a voltage of +20 mV. You know the potassium conductance (G K ) and the concentration of K + on the extracellular and cytoplasmic sides of the membrane([K + ] out and [K + ] in ). Write an equation that will give you the current through the K channels.
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MCDB 151/251 Name ___________________________________________ 3 6-10) (15 pts; 3 pts each) Multiple Choice—select ONE answer, and enter the letter on the space provided: _____6) When a neuron fires an action potential, the time of highest sodium channel conductance is a) at the resting potential b) during the EPSP c) near the action potential peak d) during the afterhyperpolarization e) during action potential repolarization _____ 7) In the heart, stimulation of the vagus nerve causes a) opening of K channels in cardiac muscle cells and slowing of the heart rate b) opening of nicotinic acetylcholine receptor channels in cardiac muscle cells resulting in membrane depolarization c) inhibition of chloride channels in cardiac muscle cells and an increase of the heart rate d) more opening of calcium channels in cardiac muscle cells and an increase in heart rate e) opening of chloride channels in cardiac muscle and a decrease in heart rate _____ 8) Which of the following does NOT describe permeation of K + through the K + channel: a) waters of hydration are removed from K + ions before they cross through the selectivity filter b) K + transport across the membrane through the K channel is at least 1000 times faster than through an ATPase pump c) permeability for K + ions compared to Na + ions is ~ 10 4 :1 d) more than one K + ion may be in the channel at the same time e) K + ions interact with amino acid side chains in the GYG selectivity filter f) repulsion between K + ions speeds their rate of travel through the channel _____ 9). The voltage sensor of potassium channels contains: a) an N-terminal region of the channel that forms a “ball and chain”
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151_Final_2007 - MCDB 151/251 Name Final Exam Fall 2007 200...

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