Question

Which of these ions are involved in muscle contraction?

• A. $C{a}^{2+}$ and $M{g}^{2+}$
• B. $C{a}^{2+}$ and $N{a}^{+}$
• C. $N{a}^{+}$ and $K^{+}$
• D. $M{g}^{2+}$ and $K^{+}$

Answer 1

The correct option is A $C{a}^{2+}$ and $M{g}^{2+}$

• Active sites for myosin(Thick filament) are present on actin which are masked by troponin in resting state. when Ca++ level increases it leads to the binding of calcium with a subunit of troponin on actin(thin) filaments and thereby remove the masking of active sites for myosin.
• Utilizing 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 actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction.
• Magnesium also plays a role in regulating muscle contractions. Magnesium acts as a natural calcium blocker to help muscles relax. Hence Ca++ and Mg++ ions are involved in muscle contractions.
• So, the correct answer is 'Ca${}^{2+}$ and Mg${}^{2+}$'.