Human Body Muscles
The muscles of the human body that work the skeletal system, that are under voluntary control, and that are concerned with movement, posture, and balance. Broadly considered, human muscle—like the muscles of all vertebrates—is often divided into striated muscle (or skeletal muscle), smooth muscle, and cardiac muscle. Smooth muscle is under involuntary control and is found in the walls of blood vessels and of structures such as the urinary bladder, the intestines, and the stomach. Cardiac muscle makes up the mass of the heart and is responsible for the rhythmic contractions of that vital pumping organ; it too is under involuntary control. With very few exceptions, the arrangement of smooth muscle and cardiac muscle in humans is identical to the arrangement found in other vertebrate animals.
Types Of Muscles:
Skeletal muscle is what most people think of as muscle, the type that can be contracted to move the various parts of the body. Skeletal muscles are bundles of contractile fibers that are organized in a regular pattern, so that under a microscope they appear as stripes (hence, they are also called striped or striated muscles). Skeletal muscles vary in their speeds of contraction. Skeletal muscles, which are responsible for posture and movement, are attached to bones and arranged in opposing groups around joints. For example, muscles that bend the elbow (biceps) are countered by muscles that straighten it (triceps). These countering movements are balanced. The balance makes movements smooth, which helps prevent damage to the musculoskeletal system. Skeletal muscles are controlled by the brain and are considered voluntary muscles because they operate with a person's conscious control. The size and strength of skeletal muscles are maintained or increased by regular exercise. In addition, growth hormone andtestosterone help muscles grow in childhood and maintain their size in adulthood.
Smooth muscles control certain bodily functions that are not readily under a person's control. Smooth muscle surrounds many arteries and contracts to adjust blood flow. It surrounds the intestines and contracts to move food and feces along the digestive tract. Smooth muscle also is controlled by the brain but not voluntarily. The triggers for contracting and relaxing smooth muscles are controlled by the body's needs, so smooth muscles are considered involuntary muscle because they operate without a person's conscious control.
Cardiac muscle forms the heart and is not part of the musculoskeletal system. Like skeletal muscle, cardiac muscle has a regular pattern of fibers that also appear as stripes under a microscope. However, cardiac muscle contracts and relaxes rhythmically without a person's awareness.