ps6a - 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 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 ) A B C D Stage of action potential Resting potential Depolarization Repolarization Hyperpolarization Voltage-gated Na + Channel status (Open or Closed/Inactive) Closed/inactive Open Voltage-gated K + Channel status (Closed, Open) Closed Na + Flow through Na + Channel (Into axon, Zero, Out of axon) Zero Into Axon K + Flow through K + Channel (Into axon, Zero, Out of axon) Out of Axon d) What role do the Na + /K + ATP-driven pumps (present in neuronal cell membranes) play in maintaining the resting potential? The sodium/potassium pump maintains the sodium and potassium ion concentration gradients across the plasma membrane. e) Consider an experimental injection of a number of positive ions into the axonal cytoplasm of a neuron. Explain how the voltage-sensitive sodium (Na + ) channels initiate an action potential in response to this injection. If the injection results in a depolarization above threshold, many sodium channels open, allowing a local
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This note was uploaded on 11/11/2011 for the course BIO 7.012 taught by Professor Lander during the Fall '10 term at MIT.

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ps6a - MIT Biology Department 7.012: Introductory Biology -...

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