Question

Extremely low levels of ${\mathrm{Ca}}^{2+}$ may result in

• A. loss of action potential reaching the muscle fibre
• B. loss of muscle contraction
• C. failure of dissociation of troponin from tropomyosin
• D. both b and c

Answer 1

The correct option is D both b and c

The cytoplasm of the muscle fibres is called the sarcoplasm. Sarcoplasm has the sarcoplasmic reticulum (endoplasmic reticulum of the muscle fibres) which stores the ${\mathrm{Ca}}^{2+}$. These ${\mathrm{Ca}}^{2+}$ ions ultimately bring about the contraction of the muscle by means of the cross bridge cycle. Action potential causes the release of a lot of ${\mathrm{Ca}}^{2+}$. These ions bind to troponin causing a conformational change in troponin. Since troponin is bound to tropomyosin, the conformational change in troponin causes the tropomyosin to be displaced. This exposes the myosin binding sites on the actin filaments and muscle contraction can occur.