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In anatomy, flexor is a muscle that contracts to perform flexion (from the Latin verb flectere, to bend), [1] a movement that decreases the angle between the bones converging at a joint. For example, one's elbow joint flexes when one brings their hand closer to the shoulder , thus decreasing the angle between the upper arm and the forearm .
Flexion and extension are movements that affect the angle between two parts of the body. These terms come from the Latin words with the same meaning. [a] Flexion is a bending movement that decreases the angle between a segment and its proximal segment. [9] For example, bending the elbow, or clenching a hand into a fist, are examples of flexion ...
A muscle that fixes or holds a bone so that the agonist can carry out the intended movement is said to have a neutralizing action. A good famous example of this are the hamstrings; the semitendinosus and semimembranosus muscles perform knee flexion and knee internal rotation whereas the biceps femoris carries out knee flexion and knee external ...
Muscles in the Lateral compartment of leg also weakly participate, namely the Fibularis longus and Fibularis brevis muscles. Those in the lateral compartment only have weak participation in plantar flexion though. The range of motion for plantar flexion is usually indicated in the literature as 30° to 40°, but sometimes also 50°.
Structure of a skeletal muscle. A key component in lateral force transmission in skeletal muscle is the extracellular matrix (ECM). Skeletal muscle is a complex biological material that is composed of muscle fibers and an ECM consisting of the epimysium, perimysium, and endomysium. It can be described as a collagen fiber-reinforced composite.
Many nuclei are needed by the skeletal muscle cell for the large amounts of proteins and enzymes needed to be produced for the cell's normal functioning. A single muscle fiber can contain from hundreds to thousands of nuclei. [25] A muscle fiber for example in the human biceps with a length of 10 cm can have as many as 3,000 nuclei. [25]
Only skeletal and smooth muscles are part of the musculoskeletal system and only the muscles can move the body. Cardiac muscles are found in the heart and are used only to circulate blood; like the smooth muscles, these muscles are not under conscious control. Skeletal muscles are attached to bones and arranged in opposing groups around joints. [8]
Unipennate muscles are those where the muscle fibers are oriented at one fiber angle to the force-generating axis and are all on the same side of a tendon. [1] The pennation angle in unipennate muscles has been measured at a variety of resting length and typically varies from 0° to 30°. [ 1 ]