Question

Calcium ion concentration in blood affects muscle contraction. Does it lead to tetany in certain cases? How will you correlate fluctuation in blood calcium with tetany?

Answer 1

Muscle contraction is initiated by a signal sent by the central nervous system (CNS) via a motor neuron. A neural signal reaching this junction releases a neurotransmitter (acetylcholine) which generates an action potential in the sarcolemma. This spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm. An increase in Ca⁺⁺ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby removes 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. This pulls the attached actin filaments towards the centre of ‘A’ band. The ‘Z’ line attached to these actions is also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction. The process continues till the Ca⁺⁺ ions are pumped back to the sarcoplasmic cisternae resulting in the masking of actin filaments.