Analyze the key events in the initiation of muscle contraction.
a. A motor unit consists of a single motor neuron and all the muscle fibres it connects to.
b. The release of the neurotransmitter acetylcholine at the motor-end plate generates an action potential in the sarcolemma.
c. This action potential spreads and causes the release of Na+ ions into the sarcoplasm.
d. The released ions bind to troponin, causing a conformational change.
e. This change in troponin removes the masking of active sites on myosin filaments.
f. The myosin head, after hydrolyzing ATP, binds to the exposed active sites on actin.
g. This binding forms a cross-bridge, which is the first step of the power stroke.
