How are muscles arranged to allow movement?

How are muscles arranged to allow movement?

• A. They are arranged in antagonistic pairs (one contracts, the other relaxes)
• B. They are attached to bones by ligaments
• C. They push rather than pull
• D. They work independently of bones

Answer: (A)

Movement happens because muscles can only pull, so across each joint they work in opposing pairs. When one muscle contracts it pulls a bone to bend the joint, while the opposite muscle relaxes to allow that movement. To straighten the joint, the roles reverse and the other muscle contracts while the first lengthens. For example, at the elbow the biceps shortens to bend the arm, and the triceps relaxes; to straighten, the triceps contracts and the biceps lengthens. Muscles attach to bones by tendons, and joints are stabilized by ligaments, but ligaments aren’t responsible for movement and muscles don’t push.

Movement happens because muscles can only pull, so across each joint they work in opposing pairs. When one muscle contracts it pulls a bone to bend the joint, while the opposite muscle relaxes to allow that movement. To straighten the joint, the roles reverse and the other muscle contracts while the first lengthens. For example, at the elbow the biceps shortens to bend the arm, and the triceps relaxes; to straighten, the triceps contracts and the biceps lengthens. Muscles attach to bones by tendons, and joints are stabilized by ligaments, but ligaments aren’t responsible for movement and muscles don’t push.