Select the correct statements regarding mechanism of muscle...

The correct answer is option (1) as muscle contraction is initiated by a signal sent by the CNS via a motor neuron. A neural signal reaching the neuromuscular junction releases a neurotransmitter (acetylcholine) which generates an action potential in the sarcolemma. This spreads through the muscle fibre and causes the release of $\mathrm{Ca}^{2 *}$ into the sarcoplasm. Increase in $\mathrm{Ca}^{2+}$ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby remove the masking of active sites for myosin. Utilising the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge.