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How We Move - Muscle fibers consist of two main protein...

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How We Move Skeletal muscles, attached to bone by tendons, produce movement by bending the skeleton at movable joints. The connecting tendon closest to the body or head is called the proximal attachment: this is termed the origin of the muscle. The other end, the distal attachment, is called the insertion . During contraction, the origin remains stationary and the insertion moves. The force producing the bending is always exerted as a pull by contraction , thus making the muscle shorter: Muscles cannot actively push . Reversing the direction in which a joint bends is produced by contracting a different set of muscles. For example, when one group of muscles contracts, an antagonistic group stretches, exerting an opposing pull, ready to reverse the direction of movement. The contracting unit is the muscle fiber
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Unformatted text preview: . Muscle fibers consist of two main protein strands - actin and myosin . Where the strands overlap, the fiber appears dark. Where they do not overlap, the fiber appears light. These alternating bands of light and dark give skeletal muscle its characterisitc striated appearance. The trigger which starts contraction comes from the motor nerve attached to each muscle fiber at the motor end plate . Acetylcholine is released at the motor end plate when the electrical impulse reaches the muscle fiber. As it binds to receptors on the surface of the muscle cells, it causes the electrical impulse to be transmitted in both directions along the fiber, activating the actin and myosin strands. The strands slide past each other to flex, or to shorten, the fiber, thus producing contraction....
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