WACE Physical Education Studies Practice Questions

A motor neuron impulse reaches the neuromuscular junction and triggers the release of calcium from the sarcoplasmic reticulum [1]. Calcium binds to troponin on the actin filament, causing tropomyosin to move and expose the myosin-binding sites on actin [1]. Myosin heads (cross bridges) attach to these exposed sites on actin [1]. Using energy from ATP, the myosin heads perform a power stroke, pulling the actin filaments towards the centre of the sarcomere (the H zone and I band narrow while the A band length stays the same, and the Z lines are pulled closer together), shortening the sarcomere [1]. ATP binds to myosin, causing the cross bridge to detach and reset before reattaching further along the actin for the next stroke [1]. This cycle repeats for as long as nerve impulses continue to arrive and calcium remains available, allowing each of the 10 repetitions to produce the same shortening action; when the impulses stop, calcium is pumped back into the sarcoplasmic reticulum, the binding sites are covered again and the sarcomere returns to its resting length [1]. Accept other relevant answers.