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How do flexor, extensor, adductor, and abductor muscles move body parts?
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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.
Muscles are categorized by their functional roles in moving body parts, primarily by acting upon the joints to which they are attached. These movements are defined as follows:1
- Flexor muscles: These muscles decrease the angle between two bones at a joint, such as when bending the elbow or knee.23
- Extensor muscles: These muscles perform the opposite action, increasing the angle between members of a limb, such as straightening the elbow or knee.43
- Adductor muscles: These muscles draw a body part, such as a limb, toward the median line or the axis of the body.513
- Abductor muscles: These muscles move a limb or body part away from the midplane or axis of the body, such as raising the arms to the side.613
These functional groups work in coordination to facilitate complex movements, such as the combination of flexion, extension, abduction, and adduction required for circular motions like circumduction.3