is a connective tissue
, whose primary purpose is to contract
. Muscle contraction is used to move parts of the body
, as well as to move substances within the body,
There are three general types of muscle. The first two are "striated", they contain sarcomeres; the third type is "smooth":
- cardiac muscles - these are formed found within the heart
- skeletal muscles - these are attached to the skeleton and used to facilitate movement
- smooth muscles - these are found within the intestines and blood vessels.
Contraction and Relaxation
The three types of muscles have significant differences, but all use the movement of actin, against myosin, to produce contraction and relaxation. Contraction is stimulated by electrical impulses transmitted by the nerves, and by the motor nerves and motoneurons in particlular. Muscles and muscular activity account for a lot of the body's energy consumption.
Muscle is composed of muscle cells (sometimes known as "muscle fibers"). Within the cells are myofibrils; myofibrils contain sarcomere, which is composed of actin and myosin. Muscle cells are grouped together into bundles of fascicle; the bundles are then grouped together to form muscle.
Exercise is often reccomended as a means of improving motor skills. Excerise does not increase the number of muscle cells, but it can improve aerobic capacity, muscle mass, and strength.