PART - 2 - Unit V : CH - 17 Locomotion and Movement — BIOLOGY STD 11 Science — Question

The stimulus for muscle contraction is provided by the motor nerves through the release of a chemical called acetylcholine at the neuromuscular junction. This chemical increases the permeability of sodium ions in the muscle fibre membrane. Sodium ions enter the muscle cell, creating a positive charge on the interior surface of the plasma membrane. This positive charge spreads throughout the entire plasma membrane and generates an action potential. Consequently, the action potential spreads across the entire plasma membrane, leading to the production of an active force on the muscle. This is how muscles are stimulated for contraction.