Chapter 11 - Neurophysiology Activities

K channels close na channels go from an inactivated

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K + channels close. Na + channels go from an inactivated state to a closed state. (Voltage-gated K + channels are opened by depolarization. This means that as the membrane potential repolarizes and then hyperpolarizes, these K + channels close. With the closing of voltage-gated K + channels, the membrane potential returns to the resting membrane potential via leakage channel activity. Resetting voltage-gated Na + channels to the closed (but not inactivated) state prepares them for the next action potential.) 20 Tetraethylammonium (TEA) blocks voltage-gated K + channels such that K + cannot pass even when the channels are open. However, TEA leaves K + leakage channels largely unaffected. How would you expect the action potential to change if you treated a neuron with TEA? The action potential would depolarize as usual, but the repolarization phase would take longer, causing the action potential to be more broad in time. (The passage of K + ions through open voltage-gated K + channels is an important component of the repolarization phase of the action potential. However, repolarization would still occur (albeit more slowly) in the presence of TEA. Once voltage-gated Na + channels open during the depolarization phase, those same Na + channels quickly inactivate. In other words, open Na + channels inevitably inactivate regardless of whether K + channels open or not. This means that the depolarization phase of the action potential stops on its own. Once Na + channels inactivate, the membrane potential is set by other open channels. If voltage-gated K + channels are blocked by TEA, then the membrane will be (slowly) set, by leakage channels, to the resting membrane potential.) 21 The diffusion of what ion, across the neuronal membrane, is responsible for the local currents that depolarize regions of the axon to threshold? Na + (sodium) 22 An action potential in one segment of axon causes adjacent sections of axon membrane to reach threshold through what mechanism? the generation of local currents 23 During action potential propagation in an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction? The previous axonal segment is in the refractory period. 24 In a myelinated axon, how do the nodes of Ranvier differ from other segments of the same axon? The nodes are more permeable to ions. 25 Where are action potentials regenerated as they propagate along a myelinated axon? at the nodes of Ranvier
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26 How do action potential propagation speeds compare in myelinated and unmyelinated axons? Propagation is faster in myelinated axons. 27 The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________. saltatory conduction 28 The myelin on myelinated neurons can be degraded or destroyed in diseases such as multiple sclerosis-a process called demyelination. If a myelinated neuron was affected by demyelination, how would this affect action potentials in that neuron?
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  • Winter '09
  • PARKER
  • Anatomy, axon terminal

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