Skeletal striated muscle

From fibre to sarcomere: myofibrils, actin, myosin, sarcoplasmic reticulum and sliding filaments.

The outline, topic by topic

Each topic is weighted the way the exam weighs it.

Muscle fibre: what is it?
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The long, multinucleated cell of skeletal muscle.
It can be several centimetres long.
During contraction, which part of the sarcomere keeps its length?
- The A band
- The I band
- The H zone
- The whole sarcomere
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The A band
The A band is as long as the thick filaments, which slide without shortening: only the non-overlap zones, the I band and the H zone, shrink.
Myofibril: what is it?
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A bundle of contractile filaments filling the fibre, divided into sarcomeres.
Its alternating bands give the striation.
Why is it called the sliding filament theory?
- Thin and thick filaments both shorten
- Thin filaments slide along thick ones without changing length
- Myosin heads shorten and pull the Z line
- Sarcomeres slide over one another along the fibre
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Thin filaments slide along thick ones without changing length
Shortening comes from greater overlap.
Sarcomere: what is it?
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The contractile unit between two Z lines.
Muscle shortens when its sarcomeres shorten.