Full Muscle Cell Types Description
[Continued from above] . . . of smaller cables, and each bundle surrounds still smaller ones. The first and largest bundle is made up of muscle fibers in which there are nerves, blood vessels, and connective tissue. Each fiber is built up from smaller strands called myofibrils, and each myofibril contains interlaced filaments of muscle proteins. Nerve impulses bring about muscle contraction and contraction causes fiber shortening so light and dark fibers become closer together. As contraction of the muscle ends, fibers relax and normal muscle length is once again attained.
Specifically, cardiac muscles, found only in the heart, power the action that pumps blood throughout the body. The smooth muscles meanwhile surround or are part of the internal organs. They are concerned with the movements of organs, such as the contractions of the uterus during childbirth. Many parts of the body contain these smooth muscles: for instance the bronchi of the lungs, the bladder, and the walls of the blood vessels. Smooth muscle is made up of long, spindle-shaped cells. In most hollow organs, these cells are arranged in bundles organized in an outer longitudinal layer and an inner circular layer. Both cardiac and smooth muscles are called involuntary muscles, because they cannot be consciously controlled.
The third of the types of muscles are called skeletal muscles. These carry out voluntary movements and are what ache after strenuous exercise. Skeletal muscles are the body's most abundant tissue, comprising about 23% of a woman's body weight and about 40% of a man's body weight.