Your heartbeat is the regular, pulsing sensation in your arteries that occurs when your heart contracts and rests. Your heart rate is the number of times your heart beats each minute. Several nerves influence your heart rate and heartbeat, with different types of nerves taking the lead in different situations.
Basics
The nerves that service your heart are part of your body's autonomic nervous system. You can't consciously control this system. Instead, it functions on its own and reflects both physical and emotional changes in your environment. When you experience stress or physical danger, a portion of your autonomic system, called the sympathetic nervous system, triggers increases in your heart rate and blood pressure, and also slows down your normal digestion. During safe, non-stressful moments, another portion of your autonomic system, called the parasympathetic nervous system, lowers your heart rate and blood pressure, and also returns your digestion to its normal speed.
Parasympathetic Effects
Your heartbeat originates in a group of cells in your upper heart called the sinoatrial or SA node. The rate set by the SA node is then passed to your lower heart through another group of cells called the atrioventricular or AV node. Without the influence of the autonomic nerves, the SA node would naturally keep the heart rate of a young adult at roughly 100 to 115 beats per minute. However, a pair of parasympathetic nerves called the vagus nerves exert partial control over the SA and AV nodes in normal situations and drop the average heart rate down to 60 to 80 bpm.
Sympathetic Effects
When you experience physical or emotional stress, your vagus nerves' influence on your heart rate drops considerably. In their place, sympathetic nerves in your heart's SA and AV nodes activate and allow your heart rate to accelerate to higher levels. Both your sympathetic and parasympathetic nerves rely on special chemical receptors to relay their signals to your heart's cells. The receptors that relay messages from your sympathetic nerves are called beta-andrenoceptors, while the receptors for your parasympathetic nerves are called muscarinic receptors.
Considerations
Other influences on your heartbeat include fluctuations in your body's core temperature and a thyroid hormone called thyroxine. In addition to your heart, you have sympathetic nerves in the outer linings of arteries and veins throughout your body. In stressful situations, these nerves trigger blood vessel tightening, or constriction. You have additional parasympathetic nerves in the blood vessels that supply your gastrointestinal and salivary glands, as well as the erectile tissue in your genital organs. Consult your doctor for more information on the ways your nerves influence your heartbeat.
References
- Medline Plus: Pulse; February 22, 2009
- Cardiovascular Physiology Concepts: Control of Heart Rate; Richard E. Klabunde, Ph.D.; April 6, 2007
- Cardiovascular Physiology Concepts: Autonomic Innervation of the Heart and Vasculature: Richard E. Klabunde, Ph.D.; March 19, 2008
- University of Washington: The Autonomic Nervous System
- Cardiovascular Physiology Concepts: Adrenergic and Cholinergic Receptors in the Heart; Richard E. Klabunde, Ph.D.; March 29, 2007
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