Fo complex, with its proton pore, is composed of three subunits, a, b, and c, in the proportion ab₂ C_n, where n ranges from 8 to 15 in various organisms; in yeast, it is 10.

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#Unit 7. System Physiology – Animal

The net movement of positive charge out of the cell due to K+ efflux at this time helps complete the process of repolarization

Relative refractory period

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#Unit 7. System Physiology – Animal

The slow return of the K + channels to the closed state also explains the after-hyperpolarization, followed by a return to the resting membrane potential

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#Unit 7. System Physiology – Animal

Sodium channels can be blocked by a toxin called tetrodotoxin when it is applied to the outside of the cell membrane (activation gates)

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#Unit 7. System Physiology – Animal

Tetraethylammonium ion blocks the potassium channels when it is applied to the interior of the nerve fiber.

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#Unit 7. System Physiology – Animal

All-or-none action potentials

the minimal intensity of stimulating current (threshold intensity) that, acting for a given duration, will just produce an action potential. The thresholdintensity varies with the duration; with weak stimuli it is long, and with strong stimuli it is short

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#Unit 7. System Physiology – Animal

During the refractory periods, excitable cells are incapable of producing normal action potentials