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Physiology Quiz -
Neuronal Action Potential - Part 5
Excitable cells of the nervous system (i.e., neurons) generate nervous impulses. Nervous impulses are the electrical signals by which neurons talk to one another and also to other cells of the body. The nervous impulse is referred to as the action potential. An action potential is a brief (only a few milliseconds) reversal of the membrane potential (Vm). At rest, the Vm of a neuron is around −70 mV (closer to the equilibrium potential for potassium, VK), but during an action potential, Vm transiently approaches +50 mV (closer to the equilibrium potential for sodium, VNa). The membrane potential then rapidly returns to the resting potential and even briefly goes beyond the resting potential to approach VK before finally returning to the resting value of about −70 mV. The entire process takes about 3-5 ms. This potential reversal of more than 100 mV is responsible for electrical signaling in the nervous system, and is the basis of information transmission in the nervous system.
(1)   Action potentials are all-or-nothing.
(2)   The threshold voltage is approximately the same for voltage-gated Na+ and K+ channels of neurons.
(3)   The Hodgkin cycle represents an example of a positive feedback loop.
(4)   During a typical neuornal action potential, the intracellular and extracellular concentrations of K+ and Na+ change significantly.
(5)   Similar to the neuronal action potential, graded potentials are all-or-nothing.
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Posted: Wednesday, September 30, 2015