Contractability of the Muscles

Muscle Contraction

By R. Marsh Ph.D.

Muscle contraction is the tightening, shortening, or lengthening of muscles when you do some activity.

Skeletal muscles contract and relax to mechanically move the body.

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Messages from the nervous system cause these muscle contractions.

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(1) A message travels from the nervous system to the muscular system, triggering chemical reactions.

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(2) The chemical reactions lead to the muscle fibers reorganizing themselves in a way that shortens the muscle--that’s the contraction.

• Open channels allow an influx of sodium ions into the cytoplasm of the muscle fiber.

• The sodium influx also sends a message within the muscle fiber to trigger the release of stored calcium ions.

• The calcium ions diffuse into the muscle fiber.

• The relationship between the chains of proteins within the muscle cells changes, leading to the contraction.​

(3) When the nervous system signal is no longer present, the chemical process reverses, and the muscle fibers rearrange again and the muscle relaxes.

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​Label the parts

Thick Myosin Filament

Thin Actin Filament

Elastic Thin Filament

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I Band

A Band

Z Disc

H Zone

M Line​

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Sarcomere:

a structural unit of a myofibril in striated muscle​

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