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How do parasympathetic nerves slow the heart rate?
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human cardiovascular system
The human heart is both a pump and a muscle. Its four chambers move blood efficiently, while cardiac muscle cells joined by intercalated disks synchronize each contraction.
The parasympathetic nervous system, specifically through the vagus nerve, regulates the heart rate by acting as a cardiac inhibitor.1
When the parasympathetic nervous system is stimulated, it exerts its influence on the sinoatrial (SA) nodeāthe heart's natural pacemakerāin two primary ways:
- Increasing the resting potential: This makes the membrane potential of the SA nodal cells more negative, moving them further away from the critical threshold required to trigger an action potential.2
- Decreasing the rate of diastolic depolarization: This slows the spontaneous upward drift of the membrane potential toward the critical level, meaning it takes longer for the cells to reach the point of firing an action potential.2
By depressing the rate of impulse formation and reducing atrial contractility, these neural signals effectively slow the heart rate, a process that typically occurs during periods of rest.21