the nerves and the nervous system
Muscles can contract and shorten
muscles
brain cells send messages to muscle cells to contract muscles
A Nerve cell tells a muscle when to contract.
muscle fibers contract the muscles when stimulated.
Involuntary muscles contract subconsciously.
The muscles that cause the lungs to expand and contract and those in the windpipe are part of the muscular system. The circulatory system carries Oxygen from the lungs to the muscles, then carries carbon dioxide from the muscles to be expelled by the lungs. The blood vessels throughout the body have integrated muscle.
Muscles contract to facilitate movement. Tendons attach muscles to bones. Ligaments attach bones to other bones.
afferent
It means your muscle is in use
Skeletal muscles .
The intercostal muscles, (muscles between the ribs), contract.