They are caused by the presynaptic neuron releasing neurotransmitters from the terminal bouton at the end of an axon into the synaptic cleft.

When there is a change in voltage in the terminal bouton, voltage-gated calcium channels embedded in the membranes of these boutons become activated.

The presynaptic terminal bouton is filled with vesicles containing acetylcholine and a neuropeptide called Calcitonin gene-related peptide (CGRP).

During stimulation of the muscle cell, the motor neuron releases the neurotransmitter acetylcholine, which travels across the neuromuscular junction (the synapse between the terminal bouton of the neuron and the muscle cell).

Amphetamines and methamphetamine are similar in structure to dopamine, and so can enter the terminal bouton of the presynaptic neuron via its dopamine transporters as well as by diffusing through the neural membrane directly.