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Pacemaker sympathetic/parasympathetic responses

If the pacemaker of the heart generates it's own beat, why is the sympathetic and parasympathetic attached to the pacemaker? How and why would the sympathetic and parasympathetic responses be called upon? What regulates this mechanism? Be very specific.

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The sinoatrial node (pacemaker) of the heart has an inherent rhythm, typically upwards of 100 beats per minute. The heart also has a built-in regulatory system in the form of the autonomic nervous system. The sympathetic nervous system serves to increase the heart rate and the force with which it contracts, and the parasympathetic nervous system does just the opposite. As a result we have a finely tuned "pump" which can react quite intricately to the body's metabolic needs. (It turns out that the parasympathetic system slightly "wins out" over the sympathetic system -- this is why our resting heart rate is usually around 80).
<br>The regulation of this system is fairly complex. ...

Solution Summary

The heart's pacemaker and its relationship to sympathetic/parasympathetic responses is discussed.