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How do skeletal muscles move bones at joints?
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muscle
The structure of striated, or skeletal, muscle. Striated muscle tissue, such as the tissue of the human biceps muscle, consists of long fine fibers, each of which is in effect a bundle of finer myofibrils. Within each myofibril are filaments of the proteins myosin and actin; these filaments slide past one another as the muscle contracts and expands. On each myofibril, regularly occurring dark bands, called Z lines, can be seen where actin and myosin filaments overlap. The region between two Z lines is called a sarcomere; sarcomeres can be considered the primary structural and functional unit of muscle tissue.
Skeletal muscles move bones at joints by functioning as part of a mechanical lever system. Because muscles can only generate force by contracting, they are typically arranged in antagonistic pairsâgroups of muscles with opposite effectsâto allow for movement in different directions.12
The process involves the following key components:
- Attachment: Muscles are attached to bones by tendons, which are strong, fibrous connective tissues that transmit the mechanical force of muscle contraction to the skeleton.31
- Leverage: Each muscle has an origin (a more stable attachment site) and an insertion (the site on the bone being moved). When a muscle contracts, it pulls on the bone at its insertion point, causing the skeletal element to rotate or move at the joint.1
- Antagonism: To reverse a movement, the opposing muscle in the pair contracts while the first muscle relaxes. For example, the biceps and triceps work together to bend and straighten the arm, respectively.1
This coordinated system is regulated by the nervous system, which adjusts muscular tension to produce precise movements.4