Ann Gaylord, age 11, of Winnipeg, Manitoba, Canada, for her question:
WHAT MAKES YOUR HEART BEAT?
Your heart is a muscular organ about the size of your fist. It pumps blood to all sections of your body, carrying nourishment on its trip away from the heart and carrying off waste materials on the return trip. It's located behind the foremost, flat bone of the chest, called the sternum, and is located slightly toward the left side.
The heart works a lifetime, starting even before a baby is born. It is a. most remarkable organ. The beat is steady and sure. The rate at which your heart beats varies slower when you are at rest than when you finish a physical education class. It also beats faster when you are suffering from emotional stress or depression, faster than when you are relaxed and without a care every Friday after school is out.
The rate of the heartbeat, or pacemaking, is controlled by weak electrical impulses that activate various parts of the heart muscle. The major pacemaking center is a bundle of nerve and muscle fibers called the sinuatrial node.
Instructions for an increase or decrease in the pacemaking rate come from the brain. It can also come from other parts of the nervous system and from reflexes originating within the heart itself. When there are defects in the system, such as poor conduction of the electrical impulses, the heart may have faulty rhythm, or a condition called arrhythmias.
Electrical pacemakers can be implanted by medical experts under or on the surface of the skin to stimulate the heart musculature and correct arrhythmias.
Doctors can sometimes find irregular beats of the heart. This is a condition known as murmurs. A serious disruption of the natural pacemaking, with improper co ordination between nerve impulses to the atria and ventricles of the heart, is called a heart block.
The automatic, reliable beat of your heart is one of the miracles of life. Yet we know what happens with the beat of the heart, but we can't understand or explain fully the how and why of the action.
We can actually see the beat of the heart on a sheet of paper. An electrical device is used to sense the varying patterns of the heart and record them on a tracing. The machine is called an electrocardiograph, and the graphic record it produces is called an electrocardiogram. Trained doctors can recognize various heart problems by the tracings.