CBSE Class 10 Answered

Muscle contraction is controlled by motor neurons that release the neurotransmitter acetylcholine at neuromuscular junctions. Acetylcholine than diffuses across the narrow synaptic cleft and binds to acetylcholine receptors on the membrane of the muscle cell. This results in the opening of ion channels within the receptor molecules, in such a way that a depolarizing, synaptic ion current can flow. This current triggers an all-or-nothing response in the form of an action potential across the plasma membrane of the muscle cells.

The action potential moves out in all directions from the neuromuscular junctions, resulting in stimulation of the entire muscle fiber within a few milliseconds, the contractile mechanism responds and the fiber contracts.