When a pacemaker potential in the SA node reaches threshold, A) the permeability to K⁺ increases. B) many voltage-gated Ca²⁺ channels open. C) voltage-gated Ca²⁺ channels close. D) resting membrane potential has been restored. E) permeability of the cell does not change.

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When a pacemaker potential in the SA node reaches threshold, many voltage-gated calcium channels open, allowing calcium ions to enter the cell and initiate the action potential that leads to heart contraction. This process is crucial for the generation of heartbeats.

When a Pacemaker Potential in the SA Node Reaches Threshold