The sequence of events that converts action potentials in a muscle fibre to a contraction is known as Excitation-Contraction Coupling. Here are the steps:

1. An action potential arrives at the neuromuscular junction.

2. Acetylcholine (ACh), a neurotransmitter, is released into the synaptic cleft.

3. ACh binds to receptors on the sarcolemma (muscle cell membrane), causing an influx of sodium ions into the muscle cell and an action potential to form on the sarcolemma.

4. The action potential travels along the sarcolemma and down the T-tubules (transverse tubules).

5. The action potential triggers the release of calcium ions from the sarcoplasmic reticulum, a specialized endoplasmic reticulum.

6. The calcium ions bind to troponin, a protein embedded in the muscle thin filaments. This causes the tropomyosin to shift and expose the active sites on actin.

7. The myosin heads bind to the exposed active sites on actin, forming cross-bridges.

8. The myosin heads pivot, pulling the actin filaments toward the center of the sarcomere. This is known as the power stroke.

9. ATP binds to the myosin heads, causing them to detach from actin.

10. The myosin heads hydrolyze ATP to ADP and phosphate, which provides the energy for the myosin heads to return to their original position.

11. The cycle of cross-bridge formation, power stroke, and release repeats as long as calcium ions are present.

12. When the action potential ends, calcium ions are pumped back into the sarcoplasmic reticulum, and the muscle relaxes.

This entire process is known as excitation-contraction coupling because the electrical signal (excitation) is coupled to the mechanical action of contraction.

Question

The sequence of events that converts action potentials in a muscle fibre to a contraction is known as Excitation-Contraction Coupling. Here are the steps:

1. An action potential arrives at the neuromuscular junction.

2. Acetylcholine (ACh), a neurotransmitter, is released into the synaptic cleft.

3. ACh binds to receptors on the sarcolemma (muscle cell membrane), causing an influx of sodium ions into the muscle cell and an action potential to form on the sarcolemma.

4. The action potential travels along the sarcolemma and down the T-tubules (transverse tubules).

5. The action potential triggers the release of calcium ions from the sarcoplasmic reticulum, a specialized endoplasmic reticulum.

6. The calcium ions bind to troponin, a protein embedded in the muscle thin filaments. This causes the tropomyosin to shift and expose the active sites on actin.

7. The myosin heads bind to the exposed active sites on actin, forming cross-bridges.

8. The myosin heads pivot, pulling the actin filaments toward the center of the sarcomere. This is known as the power stroke.

9. ATP binds to the myosin heads, causing them to detach from actin.

10. The myosin heads hydrolyze ATP to ADP and phosphate, which provides the energy for the myosin heads to return to their original position.

11. The cycle of cross-bridge formation, power stroke, and release repeats as long as calcium ions are present.

12. When the action potential ends, calcium ions are pumped back into the sarcoplasmic reticulum, and the muscle relaxes.

This entire process is known as excitation-contraction coupling because the electrical signal (excitation) is coupled to the mechanical action of contraction.

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