In the intestine,

1,25-dihydroxycholecalciferol induces the synthesis of calbindin D-28 K which promotes Ca2+ absorption.

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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

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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.