The number of vertebrae in a human is $\_\_\_\_$ .

Muscle contraction is initiated by a signal sent by the central nervous system by the release of $\_\_\_\_$ .

Which of the following is the correct order of arrangement of vertebrate column from the head to toe?

Choose the correct statements regarding muscle contraction.

A. A motor neuron carries a signal sent by the Central Nervous System (CNS) to the sarcolemma of the muscle fibre.

B. The neural signal generates an action potential which causes the release of $\mathrm{Ca}^{++}$into sarcoplasm.

C. Increase in $\mathrm{Ca}^{++}$inactivates the actin for breaking cross bridges.

D. Actin binds to the myosin head to form a cross bridge.

E. Shortening of sarcomere takes place, by pulling actin filaments towards the centre of ' A ' band.

Choose the correct answer from the options given below :