The O1 operator extends from position -5 just upstream of the mRNA start point to position +21 within the transcription unit.

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#Id: 5446

#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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#Id: 5447

#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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#Id: 5448

#Unit 7. System Physiology – Animal

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

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#Unit 7. System Physiology – Animal

Refractory period is divided into:

Absolute refractory period

Relative refractory period

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#Id: 5450

#Unit 7. System Physiology – Animal

The absolute refractory period overlaps with almost the entire duration of the action potential. During this period, no matter how great the stimulus, another action potential cannot be elicited.

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#Id: 5451

#Unit 7. System Physiology – Animal

The basis for the absolute refractory period is closure of the inactivation gates of the Na+ channel in response to depolarization. These inactivation gates are in the closed position until the cell is repolarized back to the resting membrane potential.