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ps6 - MIT Biology Department 7.012 Introductory Biology...

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NAME_____________________________________________________________TA__________________ SEC____ 7.012 Problem Set 6 FRIDAY November 19, 2004 Answers to this problem set must be inserted into the box outside Problem sets will NOT be accepted late. Solutions will be posted on the web. Question 1 a) Pictured below is a neuron obtained from your TA. Surprisingly, the microscopic structure of your TA’s neuron mimics that of a generalized human neuron . Label the neuron components marked with arrows and draw an arrow along the axon to indicate impulse direction of the route traveled by a nerve impulse. Figure by MIT OCW. MIT Biology Department 7.012: Introductory Biology - Fall 2004 Instructors: Professor Eric Lander, Professor Robert A. Weinberg, Dr. Claudette Gardel
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2 Question 1 continued b) In a neuron, where do the signals from the excitatory and inhibitory synapses get summed up in the decision to fire an action potential? (Circle the correct one.) Cell Body Axon Hillock Myelin Sheath Nerve Terminal Synaptic Vesicle Synaptic Cleft Shown below is a plot of the membrane potential at a single point on an axon as a function of time as an action potential travels down that axon. 0 mV Time -70 Time Point A Time Point C Time Point D Time Point B
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3 c) For each of the four time points indicated (A-D), fill in the following: the stage of the action potential, the status of the sodium and potassium channels, and the ion flux through each channel at the point along the axon where the potential is being measured. ( For the potassium channels give the answers for the voltage-gated type. ) Please use the terms provided. Time Point A B C D Stage of action potential Voltage-gated Na + Channel status ( Open or Closed/Inactive ) Voltage-gated K + Channel status ( Closed, Open ) Na + Flow through Na + Channel ( Into axon, Zero, Out of axon ) K + Flow through K + Channel ( Into axon, Zero, Out of axon ) d) What role do the Na + /K + ATP-driven pumps (present in neuronal cell membranes) play in maintaining the resting potential?
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