Matrix-associated regions (MARs) may be identified by characterizing the DNA retained by the matrix isolated in vivo (left) or by identifying the fragments that can bind to the matrix from which all DNA has been removed (right).

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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

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#Unit 7. System Physiology – Animal

Refractory period is divided into:

Absolute refractory period

Relative refractory period

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#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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#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.