Beginning with the release of neurotransmitters outline the

Beginning with the release of neurotransmitters, outline the steps of skeletal muscle contraction.

  (Include ACh, Ca2+, actin, myosin, troponin, tropomyosin...)

Solution

Step 1. There is flow of nerve impulse across the axon and it causes the release of acetylcholine.

Step 2. The impulse spreads across the sarcolemma. This is mediated by acetylcholine.

Step 3. With the entry of nerve impulse into T tubules and sarcoplasmic reticulum, there is release of calcium ions.

Step 4. Calcium ions bind with troponin, as a result, myosin binding sites on the actin are released.

Step 5. There is breakdown of ATP into ADP and phosphate and resultant activation of myosin crossbridges. The actin filaments slide over the myosin filaments.

Step 6. There is contraction of muscle fibres and muscles.

Step 7. Activation of acetylcholine by acetylcholineesterase. The flow of nerve impulse across sarcolemma is inhibited.

Step 8. Energy released from ATP breakdown is used to transport back calcium ions into sarcoplasmic reticulum.

Step 9. Myosin filaments separate from the actin filaments. Tropomyosin blocks the binding sites on actin. All this happens due to low calcium ion concentration

Step 10. Muscle fibres acquire their relaxed stage.