It occurs at the junction between muscle (or some other effector organ) and the axon end of the motor neuron. The axon end bears a motor end plate of knobbed branches. A knob or bouton of the motor end plate comes in near contact with depression called sole plate on the surface of muscle fibre. As the motor impulse reaches the synaptic knob, it activates the synaptic vesicles. They come to the surface and burst releasing neurotransmitter (e.g., acetylcholine). The neurotransmitter coming in contact with the sole plate receptors bring about excitation that causes the muscle to contract.