Jim Everett, age 12, of Weston, Connecticut, for his question:

What makes involuntary muscles work?

Muscle motion is triggered by nerves and powered by electrochemical energies. The sensitive nerves may spring into action when prodded by outside events such as heat and cold. In most cases they are stimulated by chemicals inside the body. The various processes of muscular motion are governed by a vast assortment of highly complex, immensely energetic biological chemicals.

All muscle motions are part and parcel of the body's fantastic system of metabolism. The body's complicated system converts the raw materials of food and oxygen into useable energies and biological chemicals. It also directs these chemicals to perform a countless number of assorted duties. A vast number of the body's muscles operate automatically, without conscious or voluntary orders from the brain. The involuntary muscles of the heart beat automatically, muscles of the respiratory and digestive systems work automatically. These operations are triggered by nerves and the nerves are stimulated by complex chemical fluids that surround them and other living cells.

Another sort of involuntary muscle movement comes as a surprise. An unexpected twitch may close an eyelid or jerk some other part of the body. It occurs when the doctor uses a little rubber hammer to tap your knee. When he taps the right spot, an involuntary reflex makes you kick up your foot. Certain poisons, often created by viruses, force the nerves to stimulate the muscles. They contract with involuntary jerks, one after another, and the body suffers serious spasms.

Lab experiments prove that muscle fibers can be stimulated by light electric shocks. But inside the body almost all of their motion is triggered by nerves. The nerves themselves may be stimulated by heat, blows and other painful outside events. But almost all of their activity is governed by surrounding biochemicals. One of these is acetylcholine, another is adenosine triphosphate    alias ATP. There are more than a score of these energetic chemicals, each one as complicated as its fancy name.

The body fluids that govern the processes of metabolism must be kept correctly balanced. And the amount of this or that chemical in the mixture changes from moment to moment. The chemical ingredients are constantly reacting with each other and changing. When atoms and molecules arrange and rearrange themselves, electrons shift from one particle. to another. This creates ion particles,, charged with positive or negative electricity. These ceaseless, (reactions create electrochemical energies. The charged ions create the electric power that stimulates the nerves to trigger the muscles. Most of the voluntary and involuntary movement of muscles is powered by this complicated chemistry of metabolism. However, an involuntary jump from a hot stove occurs when nerves react to a stimulus outside the body.

The basic work of metabolism goes on in the submicroscopic world of biochemicals within the living cells and in the fluids  around them. But all of these small units are organized to work together in harmony with all the other systems of the whole body. All the nerves are linked with the brain headquarters. Voluntary muscular motions are decided by conscious brain centers. Involuntary motions are governed by unconscious parts of the brain    which is why we have no conscious control over them.