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6 years ago
Explain the difference between a graded potential and an action potential at the level of the cell membrane and ion movement?
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6 years ago
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A graded potential is a voltage change, positive or negative, in the membrane potential that:

1. varies in magnitude according the magnitude of the stimulus (unlike an action potential which always has the same magnitude, regardless of the magnitude of the stimulus).  The larger the stimulus, the larger the graded potential.

2. does not have a threshold (unlike action potentials, which do, because action potentials are triggered by the opening of voltage-gated sodium channels once threshold is reached).

3. does not have a refractory period (unlike action potentials, which do, because their voltage-gated sodium channels have to complete a cycle).

4. can occur in any cell's membrane (unlike action potentials, which can only occur in cells with excitable membranes).

5. dimishes in strength as it travels along the membrane (unlike an action potential which retains its strength all the way down an axon).  Graded potentials spread passively, not actively (that is, not via voltage-gated ion channels, as action potentials do).

In general, in neurons, graded potentials occur in dendrites and the soma, whereas action potentials occur along axons.
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