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Control of Heart by Sympathetic and Parasympathetic Nerves

Sympathetic Nervous System

  • Supplies SA node, AV node as well as ventricular musculature.

  • Baseline activity keeps the heart pumping 30% above that without sympathetic activity.

  • Increases heart rate by stimulating the SA node.

  • Increases force of contraction by stimulating ventricular muscle cells.

  • The net result is increased cardiac output.

  • Decreases heart rate.

  • Decreases force of contraction decreases.

  • The net result is decreased cardiac output.

Parasympathetic Nervous System

  • Mainly supplies SA node and atria but not much to ventricles.

  • Calms down the heart.

  • Mainly decreases heart rate.

  • not much effect on the force of contraction as ventricles do not receive significant parasympathetic innervation.

Very Strong Stimulation

Stop the heart for a few seconds

Heart Escapes

The heart starts beating at a lower rate of 20-40 beats per minute

  • Decrease strength of contraction to some extent.


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