Prolonged Refractory Periods Prevent The Heart From Being Tetanized

The fast sodium channels trigger action potentials in contractile and Purkinje cells. They have actually two gates that control passage of Na+ through the channel. The activation gate normally blocks the channel. Because it is voltage-gated it opens only when the membrane potential reaches threshold creating phase 0. Shortly after the activation gate opens a second part of the molecule, the inactivation gate closes the channel, causing phase 0 to end. The inactivation gate is voltage sensitive and does not reopen until the membrane repolarizes. Only when the inactivation gate finally

FIGURE 6 Effects of sodium channel blocker, tetrodotoxin (TTX), on action potential in a contractile cell. TTX affects the early phases (phases 0 and 1), but has little effect on phases 2 and 3.
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    What prevents the heart from being tetanized?
    7 years ago

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