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19 Cards in this Set

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  • Back
What are resting membrane potentials?
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.
At rest the membranes of nerve cells are far more permeable to ___ +____ than to ____+___
K + Cl, Na + Ca
Na+ - K+ ATPase is necessary for the creation and maintenance of the K+ concentration gradient, which establishes the ____ ____ ____
resting membrane potential
An action potential is a property of _____ cells
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
Each action potential exhibits propagation – an action potential at one site cause depolarization at adjacent sites, bringing those adjacent sites to _____
threshold
Propagation of action potentials from one site to the next is ________.
nondecremental
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
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
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.
What is repolarization?
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.
What is Hyperpolarizing after potential?
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
Eventually ___ conductance returns to resting level, membrane potential depolarizes slightly, back to resting potential.
K+

Membrane is now ready to generate another action potential if stimulated.
What happens during a refractory period?
nerve cells are incapable of producing action potentials with normal stimulation.
What is an absolute refractory period?
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.
What is a Relative refractory period?
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.
Propagation of Action Potentials occurs by what?
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.
Myelination increases or decreases conduction velocity? Why?
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.
At these nodes of Ranvier resistance is ____ and current can flow therefore action potentials can occur.
low
The action potentials jump from node to node, this is called what?
saltatory conduction