Question

Briefly describe the steps involved in the initiation of a contraction in a skeletal muscle fibre. List the steps in the order that they occur. Start with an action potential on the sarcolemma and end with a description about how cross-bridges form. Include details about the intracellular structures and ion/s involved. You should provide 8 pieces of relevant information to obtain 8 marks.

Answer 1

Steps involved in musclr contraction :

1. The action potential tranmitted through the nerves reaches the neuromuscular juction.
2. Acetylcholine is released at the neuromuscular junction through the vesicles.

3. Acetylcholine released binds to the receptors on the  sarcolemma and results in opening of sodium channels. This leads to generation of action potential within sarcolemma.
4. The action potential travels through t tubules within the cell.
5. This results in release of calcium from the sarcoplasmic reticulum.
6. The calcium binds to troponin and the myosin binding site on the actin is freed.
7. myosin binds to the actin resulting in formation of cross bridge.
8. power stroke : during power stroke, the myosin head undergoes conformational change resulting in release of ADP.
9. ADP binds to phosphate resulting in formation of ATP which binds to myosin head resulting in detachment of actin myosin cross bridge.
The muscle relax.
10. The calcium released from sarcoplasmic reticulum is pumped back into it.