Modern measurements require just a drop of blood, added to a test strip containing the enzyme glucose oxidase

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#Unit 7. System Physiology – Animal

Phase 0 (depolarization), fast sodium channels open. 

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#Unit 7. System Physiology – Animal

Phase 1 (initial repolarization), fast sodium channels close.

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#Unit 7. System Physiology – Animal

Phase 2 (plateau), calcium channels open and fast potassium channels close

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#Unit 7. System Physiology – Animal

Phase 4 (resting membrane potential) averages about −90 millivolts.

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The SA node exhibits automaticity; it can spontaneously generate action potentials without neural input. 

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#Unit 7. System Physiology – Animal

SA node has an unstable resting membrane potential.

The “resting membrane potential” of the sinus nodal fiber between discharges has a negativity of about −55 to −60 millivolts.