Which of the following is the correct sequence of steps in muscle contraction from start to finish (1-6)?
a) Calcium ions bind to troponin, exposing myosin binding sites on actin
b) Action potential travels along the sarcolemma and down the T-tubules
c) ATP binds to myosin heads, causing them to detach from actin
d) Calcium ions are released from the sarcoplasmic reticulum into the cytoplasm of the muscle cell