What are the 4 stages of muscle contraction?

1: Sarcolemma depolarization and calcium ion release (nerves stimulate muscle fibre) 2: Actin and myosin cross-bridge formation (Exposes binding sites on A and M) 3: Sliding mechanism of actin and myosin filaments (actin filaments moves across the myosin) 4: Sarcomere shortening (muscle fibres contract = movement)