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Muscle is the tissue that makes it possible for a person or animal to move from place to place. The muscle makes the heart beat; forces the blood to circulate; and pushes the food through the digestive system.
Types of Muscles
1. Skeletal (striated or voluntary) muscles are attached to the skeletons, causing the bones to move. They make a large part of the arms, legs, chest, abdomen, neck and face.
All muscles are made up of cells called muscle fibers. Skeletal muscle fibers differ in appearance from the smooth muscle fibers. A fiber of skeletal muscle is long and slender that lie parallel to each other in bundles. They show alternating light and dark bands called striations. So skeletal muscles are also called striated muscles.
To do its job, both ends of a skeletal muscle must be attached to the skeleton. The end of the muscle that normally does not move and is closest to the central part of the body is called the origin. The end of the muscle that is attached to the bone it move is called the insertion. Flexor is a muscle that bends a joint and brings a limb closer to the body while extensor is a muscle that does the opposite. Skeletal muscles usually move voluntarily (under conscious control) so they are also called as voluntary muscle. But they may also move involuntarily (without conscious control). Skeletal muscles must be stimulated by a nerve or they will not operate. When one suffers a nerve injury, they will not operate. Paralysis may result if a person suffers from a nerve or a spinal cord injury.
2. Smooth (non-striated or involuntary) muscles differ from the skeletal muscles in structure, location and the way to they contract. The walls of the stomach and intestines have sheets of smooth muscles arranged in circular and lengthwise patterns. These muscles contract slowly and rhythmically to move the food along for digestion. The smooth muscle in blood vessels can relax to make the vessels opening wide, or contract to make them narrow.
The smooth muscle fibers do not have striations so they are called non-striated muscles. They do not have to be stimulated directly by a nerve to operate. Hormones can make the smooth muscles to work.
Smooth muscles cannot be controlled voluntarily so they are called as involuntary muscles.
3. Cardiac (heart) muscles resemble both the skeletal and smooth muscles. They have striations like the skeletal but they cannot be controlled voluntarily like the smooth muscle. A special regulator of the heart called sinoatrial node gives off rhythmic stimulations that cause the heart muscle to contract.