Term
| Describe passive membrane behavior. |
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Definition
| This is when a membrane has only voltage independent leak channels. So, Vm stays pretty much constant after a current ends. |
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Term
| Describe active membrane behavior. |
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Definition
| This is when a cell membrane has voltage-gated channels. So, conductance of the membrane responds to changes in Vm. |
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Term
| What's an excitable membrane? |
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Definition
| This is where changes in Vm (threshold depolarization) cause an action potential. |
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Term
| What is an action potential? |
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Definition
| An all-or-nothing stereotyped sequence of changes in Vm |
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Term
| Can an action potential that starts at one part of the membrane move to other parts of it? |
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Definition
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Term
| What happens during a neuron action potential? |
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Definition
| First, you have a little depolarization, then a huge spike in depolarization, then a small hyperPOLARization, then back to original Vm. |
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Term
| Describe the steps (in terms of what is rushing in and out) of an action potential. |
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Definition
| First, have depolarization with Na+. Then, K+ channels open right at the peak of depolarization. Then K+ rushes out, until rePOLarization. K+ channels close sometime during the repolarization, and then the cell returns to normal Vm. |
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Term
| After the depolarization threshold happens and Na+ channels open up, what direction (in terms of voltage) does the Vm run towards? |
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Definition
| it runs towards the Veq for Na+ (ie the Vna). |
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Term
| At the peak of the depolarization, what happens in terms of opening/closing of gates? |
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Definition
| the Na+ channels close and the K+ channels open. |
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Term
| Where does the Vm run after the K+ channels are open? Why does Vm hyperpolarize and then go back to normal? |
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Definition
| The Vm runs towards Vk, and then the K+ channels close, and the K+ leak channels get the Vm back to normal. |
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Term
| What are the two different types of cardiac action potentials? |
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Definition
| 1) slow, brief type that is present in the nodes. 2) fast, prolonged type present in the contractile muscle |
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Term
| Do cardiac cells spend their time mostly depolarized or polarized? |
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Definition
| Mostly depolarized because of these long Ca2+ influxes |
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Term
| At rest, what provides the dominant conductance in cardiac cells? |
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Definition
| inward rectifying K+ channels |
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Term
| Describe the action potential of a cardiac muscle cell |
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Definition
| The cell's depolarization causes Na+ channels to open and you get hyperdepolarization, then the Na+ channels start to inactivate so you get a small repolarization, then the Ca2+ channels slowly activate, so you get a prolonged action potential. Then, K+ channels open, and K+ efflux causes repolarization until these channels also close. |
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Term
| How does depolarization spread through a cell? |
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Definition
| Once some Na+ starts rushing in, it spreads easily in the cytoplasm, causing other Na+ channels to open. |
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Term
| Does the entire action potential in an axon happen simultaneously? |
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Definition
| Not exactly. It spreads from the cell body along the axon. |
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Term
| What can slow down/hinder an action potential? |
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Definition
| The outflow of K+ from leak channels as the Na+ is rushing in. |
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Term
| Does charge traveling down an axon depend on Na+ diffusion? |
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Definition
| No, it is a faster electrotonic thing where charges are distributed across the membrane |
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Term
| Because K+ egress through leak channels decays action potentials down the axon, what can be down? |
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Definition
| myelin allows the signal to travel longer distances by preventing some of the K+ egress. Also, larger axons do better at keeping their signal for longer. |
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Term
| Besides myelin and large axons, how can axons preserve action potentials down their entire length? |
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Definition
Nodes of ranvier. At these nodes of
Ranvier, voltage-gated Na+ and K+ channels are abundant and action potentials can initiate. In this
way, the action potential “jumps” quickly from one node to the other, a behavior called saltatory conduction. |
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