Please forward this error screen to 88. Muscle action can be classified as being either voluntary or involuntary. Cardiac and smooth muscles contract without conscious thought and are termed involuntary, whereas the skeletal muscles contract upon command. Skeletal muscles in turn can be divided into fast and strength training for fat loss pdf twitch fibers.
Though this postural control is generally maintained as an unconscious reflex, the muscles responsible react to conscious control like non-postural muscles. Unlike skeletal muscle, smooth muscle is not under conscious control. Striated muscle contracts and relaxes in short, intense bursts, whereas smooth muscle sustains longer or even near-permanent contractions. Slow twitch fibers contract for long periods of time but with little force.
They contribute most to muscle strength and have greater potential for increase in mass. A skeletal muscle fiber is surrounded by a plasma membrane called the sarcolemma, which contains sarcoplasm, the cytoplasm of muscle cells. A muscle fiber is composed of many fibrils, which give the cell its striated appearance. It also protects muscles from friction against other muscles and bones. Besides surrounding each fascicle, the perimysium is a pathway for nerves and the flow of blood within the muscle. At each level of bundling, a collagenous membrane surrounds the bundle, and these membranes support muscle function both by resisting passive stretching of the tissue and by distributing forces applied to the muscle.
The term “myofibril” should not be confused with “myofiber”, which is a simply another name for a muscle cell. The striated appearance of both skeletal and cardiac muscle results from the regular pattern of sarcomeres within their cells. Although both of these types of muscle contain sarcomeres, the fibers in cardiac muscle are typically branched to form a network. Bundles of muscle fibers, called fascicles, are covered by the perimysium. Muscle fibers are covered by the endomysium. The gross anatomy of a muscle is the most important indicator of its role in the body.