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19 Cards in this Set
- Front
- Back
What are resting membrane potentials?
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Established by diffusion potentials
Result from the concentration differences for various ions across the cell membrane Resting membrane potential of nerve cells approximately –70 mv. |
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At rest the membranes of nerve cells are far more permeable to ___ +____ than to ____+___
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K + Cl, Na + Ca
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Na+ - K+ ATPase is necessary for the creation and maintenance of the K+ concentration gradient, which establishes the ____ ____ ____
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resting membrane potential
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An action potential is a property of _____ cells
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excitable
Consists of a rapid depolarization followed by a repolarizaton of the membrane potential. Action potentials are the basic mechanism for transmission of information in the nervous system. Each normal action potential for a given cell type looks identical, depolarizes to the same potential and repolarized back to the same resting potential |
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Each action potential exhibits propagation – an action potential at one site cause depolarization at adjacent sites, bringing those adjacent sites to _____
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threshold
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Propagation of action potentials from one site to the next is ________.
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nondecremental
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T or F
Action potentials exhibit all or none response, ie an action potential either occurs or doesn’t occur. |
True
If a normal cell is depolarized to threshold in a normal manner, then the occurrence of an action potential is inevitable. If the membrane is not depolarized to threshold, no action potential can occur |
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At rest membrane potential is ____ mv.
What are the states of the K and Na channels? |
-70
K+ conductance is high - K+ channels are open Cl- conductance is high Na+ conductance is low – Na+ channels are closed |
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When membranes of neuron depolarized to about –60mv reaches threshold.
Then what happens? |
Causes rapid openings of Na+ cannel activation gates
Na+ conductance becomes higher than K+ conductances: Results in an inward rush of Na+, the membrane potential is further depolarized to about 55 mv. Tetradotoxin (puffer fish) and the local anesthetic Lidocaine block these voltage-sensitive Na+ channels thereby preventing the occurrence of nerve action potentials. |
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What is repolarization?
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upstroke is terminated and the membrane potential repolarizes to the resting level.
Inactivation gates on the Na+ channels respond to depolarization by closing, however, their response is slower than the openings of the activation gates.Thus after a delay the inactivation gates lose the Na+ channels. Depolarization opens K+ channels and increases K+ conductance to values even higher than at rest. The combined effect of Na+ channels closing and increased K+ channels opening makes the K+ conductance much higher than the Na+ conductance – membrane is repolarized. |
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What is Hyperpolarizing after potential?
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For a brief time following repolarizaton, the K+ conductance is higher than at rest – the membrane potential is driven closer to K+ equilibrium potential – membrane becomes more negative <-70mv, so –75mv
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Eventually ___ conductance returns to resting level, membrane potential depolarizes slightly, back to resting potential.
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K+
Membrane is now ready to generate another action potential if stimulated. |
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What happens during a refractory period?
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nerve cells are incapable of producing action potentials with normal stimulation.
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What is an absolute refractory period?
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no matter how great a stimulus is given, another action potential cannot be elicited.
Basis for absolute refractory period is closure of the Na+ channel inactivation gates in response to depolarization. These inactivation gates remain in the closed position until the cell is repolarized to –70 mv. |
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What is a Relative refractory period?
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an action potential can be elicited but only if a supramaximal stimulus is given.
Relative refractory period begins at the end of the absolute refractory periods. Basis for relative refractory period is the higher K+ conductance than is present at rest. |
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Propagation of Action Potentials occurs by what?
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Occurs by the spread of local currents from active regions to inactive regions adjacent to.
Increasing the diameter of the nerve fiber increases the conduction velocity. |
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Myelination increases or decreases conduction velocity? Why?
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increases
Is an insulator – lipid – of nerve fibers – increases resistance At intervals 1-2mv are break sin the myelin sheath, these are nodes of Ranvier. |
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At these nodes of Ranvier resistance is ____ and current can flow therefore action potentials can occur.
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low
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The action potentials jump from node to node, this is called what?
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saltatory conduction
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