Question

Which of the following is important for muscle contraction and nerve impulse transmission?
A. $Ca^{2+}$ ions
B. $Ca^{2+}$ and $Mg^{2+}$ ions
C. $Mg^{2+}$ ions
D. $Fe^{2+}$ ions

Answer 1

Hint: The motor nerve cells transmit impulses from the brain to the muscle for contraction. The actin and myosin help in the contraction of muscle. Muscle contraction facilitates the movement.

Complete Answer:
- The impulses are transmitted through neurons. The neurons transmit impulses at the junction called the synapse where acetylcholine is released which is a neurotransmitter. It generates action potential in the sarcolemma. This causes release of the calcium ion in the sarcolemma.
- The increase in the calcium ion leads to the calcium binding with troponin on the actin filament. This utilises energy from the ATP hydrolysis and the myosin binds to the active sites on the actin. This helps in pulling off the actin filament towards the centre of the “A” band.
- The “Z” band attached to the actin is pulled which causes contraction (shortening of the sarcomere). Then the myosin again comes back to the relaxed state.
- Relaxed state is achieved when the calcium blocker i.e. the magnesium ion binds at the calcium binding site. The magnesium acts as a regulator to facilitate contraction. Ferrous ion is an important constituent of haemoglobin.

Thus the correct answer is B.

Note: The Actin and Myosin are the proteins that facilitate muscle contraction. Actin also involved the other cellular processes and chief component of the cytoskeleton in the eukaryotes. Tropomyosin is an actin binding protein which regulates the muscle contraction until a proper nerve impulse is attained.