4A+pset1+rationales

4A+pset1+rationales - 4A Problem Set 1 Rationales Part 1 1....

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4A Problem Set 1 Rationales Part 1 1. C Modified Student Rationale: “A” is false because the number of open K+ leak channels stays constant during action potentials, while “B” is false because the activity of Na/K+ pumps does not change during action potentials since they are not influenced by voltage changes. “D” is false because the voltage-gated Na+ channels open, rather than close, as a result of membrane depolarization above a certain threshold. Also, there is no way for Na+ channels to “sense” when the membrane potential has reached its maximum value, since maximum value depends largely on the activity of Na+ channels. However, “C” is true because after the voltage-gated Na+ channels open and allow Na+ into the cell, the inactivation gate closes, blocking any more Na+ from entering the cell. 2. B Dendrites on a canonical neuron contain only ligand-gated channels (to respond to neurotransmitters). These channels may be specific to Na+, K+, or potentially other ions. The first place we begin to see voltage-gated channels is at the axon hillock. 3. C The axon of a canonical neuron requires voltage-gated Na+ channels as well as voltage- gated K+ channels to propagate an action potential (recall how these channel types are involved in the different stages of the action potential). In a canonical neuron, voltage-
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This note was uploaded on 08/01/2009 for the course HUMBIO 4a taught by Professor Various during the Spring '08 term at Stanford.

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4A+pset1+rationales - 4A Problem Set 1 Rationales Part 1 1....

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