Regulation of the Heart Heart: Regulation of the Heart

The contraction of the muscle fibers in the heart is very organized and highly controlled. Rhythmic electrical impulses (discharges) flow through the heart in a precise manner along distinct pathways and at a controlled speed. The impulses originate in the heart's pacemaker (the sinus or sinoatrial node—a small mass of tissue in the wall of the right atrium), which generates a tiny electrical current (see Abnormal Heart Rhythms: Normal Electrical Pathway).

The rate at which the pacemaker sends out its impulses (and thus governs the heart rate) is determined by two opposing systems—one to speed the heart rate up (the sympathetic division of the nervous system) and one to slow it down (the parasympathetic division (see Biology of the Nervous System: Nerves). The sympathetic division works through a network of nerves called the sympathetic plexus and through the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline), which are released by the adrenal glands and the nerve endings. The parasympathetic division works through a single nerve—the vagus nerve—which releases the neurotransmitter acetylcholine.

Last full review/revision February 2006 by Paul H. Tanser, MD