TYPES OF MUSCLES Muscle Fibers

TYPES OF MUSCLES 

Each muscle is made up of a bundle of fibers, each of which is about the size of a hair and capable of supporting 1,000 times its own weight. All told, there is something more than 6 trillion fibers in the muscles throughout the body. There are three types of muscle tissue. One, when viewed under a microscope, has dark and light bands across the fibers, and is known as striped muscle. It is also called skeletal muscle because it is attached to some part of the skeleton. And it is classed as voluntary muscle because it is under the control of the conscious part of the brain. This is the type of muscle used to walk, write, lift, and throw to perform any movement we actually will to be done.

A second type of muscle, called smooth or involuntary, lacks the dark and light bands. This type of muscle handles the functions of all internal organs except the heart. It is involved in the vital movements of the stomach and intestine, for example. It is called involuntary since we do not have direct control over its action. Its workings are automatic, freeing us from concern over it, allowing us opportunity to concentrate on other matters. The third type of muscle that of the heart is called cardiac. It is striped like the voluntary type but has no sheaths as the voluntary does. It, too, is involuntary.

Muscle fibers vary considerably in length, from as little as 0.04 inch or even less to 1.5 inch or more. The diameter, of course, is very small, as little as 0.004 inch or even less. When a muscle contracts, it becomes shorter by as much as one third to one half, and as it shortens, it thickens. Most skeletal muscles are linked to a bone either at one end or at both ends. The tendons, or sinews, which do the linking, vary considerably in size, ranging up to more than a foot in length. Ligaments, like the tendons, are made up of strong fibrous tissue, but their function is to bind bones together. Tendons join muscle to bone; ligaments join bone to bone. Ligament fibers stretch. Tendons are so strong that a bone may break before the tendon attached to it gives way. When muscles join bones, one of the bones usually functions as an anchor to help move the other bone.

The point where the muscle attaches to the anchor bone is known as the point of origin. The attachment to the bone that does the moving is called the insertion. Before a muscle can contract, it must receive a contract signal. In the case of voluntary muscles, the signal comes from the brain via the central nervous system and is relayed' instantly through tiny nerves that reach each of the fibers involved. Involuntary muscles get their signals from the autonomic nervous sys- tem, which is concerned with the regulation of body functions that do not have to be under conscious control. To be sure, even in the case of voluntary muscles, you are not required to give a direct order-to take the time to stop and think and issue a command for a particular muscle to contract. You simply decide to bend an elbow, move a finger, throw a ball-and the brain and nervous system translate the decision into orders which go to the proper muscle fibers.