Practice question · Put in order
Arrange these events of skeletal muscle contraction in order.
- Myosin heads bind and pivot, pulling the filaments
- The sarcomere shortens and the muscle contracts
- Calcium is released from the sarcoplasmic reticulum
- Binding sites on the actin filament are exposed
- A nerve impulse arrives at the neuromuscular junction
Hints
- The sequence begins outside the muscle cell.
- Calcium release is what unblocks the binding sites.
Show the answer
- A nerve impulse arrives at the neuromuscular junction
- Calcium is released from the sarcoplasmic reticulum
- Binding sites on the actin filament are exposed
- Myosin heads bind and pivot, pulling the filaments
- The sarcomere shortens and the muscle contracts
Why
The chain runs from nerve signal to calcium release to exposed binding sites to cross-bridge cycling. Calcium is the switch: without it the binding sites stay covered and no contraction is possible, which is why calcium handling is central to muscle disease.
Practise Muscle and Nervous Tissue
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