Describe The transmission of a nervous impulse across a neuromuscular junction.

When an action potential arrives at the pre-synaptic knob voltage-gated calcium ion channels open, allowing calcium ions to diffuse into the synaptic knob. The influx of calcium ions causes neurotransmitter (acetylcholine) containing vesicles to exocytose acetylcholine into the synaptic cleft. Acetylcholine binds to specific sodium ion receptors on the motor end plate. Sodium ion channels open and the motor end plate becomes depolarised. Depolarisation results in the propagation of an action potential which travels down T-tubules to the sarcoplasmic reticulum.