Question

discuss the steps of how a skeletal muscle contracts.

Answer 1

1. first there has to be an action potential (nerve stimulus) reaching the motor end plate through a motor Neuron.
2. this stimulus will cause release of acetylcholine to the motor end plate.
3. acetylcholine will bind to the receptors on the motor end plate and cause an action potential in the muscle (by entry of sodium by opening sodium channels.)
4. this action potential sweeps into T tubule and stimulates the Ryanodine receptor to release of calcium from the sarcoplasmic reticulum of the muscle fibre into the sarcoplasm.
5. This calcium in the sarcoplasm bind to the troponin C. this causes a conformational change in troponin C
6. troponin C is connected to tropomyosin. when the calcium gets attached to troponin C, it will cause tropomyosin to slide over actin and this sliding of tropomyosin exposes the active sites of actin.
7. myosin heads binds to the active sites of actin and bending of myosin head takes place (this is called as a power stroke). this causes movement.
8. ATP attaches to the myosin head and cause detachment. using energy from this ATP, myosin will go back to high energy affinity state ready to attach to the next active site of actin.
9. steps 5-8 continues as long as calcium is available in the sarcoplasm of the muscle and movements can continue.
10. calcium is transported back to the sarcoplasmic reticulum by SERCA(active transport mechanism for calcium), the conformational change in the troponin C is reversed, and tropomysosin covers the active site of actin and contraction stops.