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25 Cards in this Set
- Front
- Back
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What does depolarization of the cell membrane above a certain threshold produce?
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An action potential
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What is an action potential?
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A transient, regenerative electrical impulse in which the membrane potential (Vm) rapidly rises to a peak that is ~100 mV more positive than the normal, negative resting potential (Vrest)
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What is the role of calcium in an action potential?
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Inward Ca current maintains the AP plateau.
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What is the significance of the brief AP of a nerve axon?
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Permits rapid signaling
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What does the prolonged, repetitive AP of cardiac and smooth muscle permit?
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Rhythmic contractions of these tissues.
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Will sub-threshold depolarizations trigger an AP?
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Nope, the AP will only be triggered by depolarizations that reach threshold
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Why does the AP remain constant in magnitude and shape?
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B/c excitation of voltage-gated channels in adjacent regions of the excitable membrane progressively regenerate the original response.
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What initiates rapid depolarization of an AP?
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When Vm passes the threshold, opening of voltage-gated channels initiates the rapid depolarization.
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How do APs propagate?
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At constant velocity w/o change in amplitude or shape.
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What is the absolute refractory period?
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The time after initiation of an AP when it is impossible to produce a second AP
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What is the relative refractory period?
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A second AP can be elicited but requires a stronger stimulus.
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What is the voltage of the cell at the peak of an AP?
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~+40mV
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What causes hyper-polarization after the AP has passed?
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The outward flow of Potassium
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What regulates the degree of depolarization of the membrane?
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Potassium
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How does K modulate Na conductance?
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By modulating Na channel gating activity
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What do unitary currents represent?
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The conductance of a single channel
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Why does current through a single channel increase as voltage increases?
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B/c the P0 of a single channel increases w/ increased voltage.
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What is the macroscopic current for K or Na?
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The product of a single channel conductance, (P0 of a single channel) and total number of K or Na channels
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What does conduction of an AP depend on?
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1. cell shape/anatomy
2. electrical resistance of aqueous sol'n and cell membrane 3. membrane capacitance |
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What does propagation of electrical signals in the nervous system involve?
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Local current loops
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What does myelin do in an axon?
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increases the thickness and hence cross section of the axon and increases resistance across the membrane so that current flow through the nodes is longitudinal.
This means signal decay is minimized and the speed of propagation is maximized. |
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What does tetrodotoxin inhibit?
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The voltage-sensitive Na channels, thus blocking the inward current of an AP
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What does lidocaine inhibit?
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The voltage-sensitive Na channels, thus blocking the inward current of an AP
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What do the cardiac glycosides "oubain" and "digitalis" block?
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The Na/K ATPase
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What blocks the Kv channel?
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Tetraethylammonium (TEA), this blocks re-polarization of the membrane
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