Skeletal muscles - structure and actions

 SKELETAL MUSCLES

Thanks to skeletal muscles, we can move and perform many activities. The skeletal muscles are made up of muscle belly and bundles of muscle fibers.

Muscle fibers are made up of myofibrils, which are made up of actin and myosin myofilaments.

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Muscle belly has the ability to shrink.

Tendon is strands of connective tissue that attach muscles to the bone.

Sarcomere

The sarcomere is the basic contractile unit of the skeletal muscle. Sarcomere repeats regularly along the entire length of the myofibrils.

Muscle contraction

Muscle contraction occurs as a result of a nerve impulse. The following are necessary for its course:

• calcium ions - allow actin to binds with myosin

• ATP - provides energy

1. ATP attaches to the myosin, which binds with actin.

2. ATP breaks down to form ADP and a phosphate moiety.

3. Myosin changes its position.

4. Actin fibers shift and the sarcomere shortens.

shortening of the sarcomere

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shortening of the entire myofibril

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shortening of the muscle fibers

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muscle contraction

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Antagonistic pairs 

Most muscles work in pairs - one muscle works in one direction and the other works in the opposite direction. These muscles are called antagonistic muscles pairs.

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Examples of such muscles are the biceps and triceps. 

When the biceps contract, the triceps relaxes (flexion) 

When the biceps relaxes, the triceps contracts. (extension)