What muscles contract and extend?

Muscles can contract and extend.

- Contraction is the process by which a muscle shortens. This occurs when the muscle fibers slide past each other, causing the muscle to thicken and shorten. Contraction is initiated by a nerve impulse that travels from the brain to the muscle.

- Extension is the process by which a muscle lengthens. This occurs when the muscle fibers slide past each other in the opposite direction, causing the muscle to thin out and lengthen. Extension is initiated by the relaxation of the muscle fibers.

The ability of muscles to contract and extend is essential for movement. When a muscle contracts, it pulls on the bone that it is attached to, causing the bone to move. When a muscle extends, it allows the bone to move back to its original position.

The muscles of the body are constantly contracting and extending, working together to produce smooth, coordinated movements.