What is the first step in excitation-contraction coupling?
A. Each myosin filament pulls the actin filament it overlaps with towards its centre
B. An electrical signal travels over the surface of, and along, the muscle
C. Calcium ions expose active sites on the actin filaments, to which the myosin filaments immediately attach
D. In the neuromuscular junction, a chemical is released from the end of the nerve fibre, which causes a rapid change in the voltage of the muscle
Answer: D