Human facial anatomy involves a complicated arrangement of various muscles, through the action of which both essential physiological functions are accomplished and facial expressions are produced. Armed with a detailed knowledge of the anatomical composition of the face, cosmetic practitioners can select muscles or groups of muscles to weaken or paralyse using botulinum toxin so as to improve the facial appearance of patients. Botulinum toxin acts to prevent acetylcholine from being released into the synapse, i.e. denervation by chemical means. At muscle endplates, acetylcholine is secreted from the presynaptic neuron. Cholinergic transmission depends on vesicles containing acetylcholine being able to dock with the plasma membrane and discharge into the synaptic cleft, a process that involves a number of molecular interactions, in particular those involving N-ethylmaleimide-sensitive fusion protein (NSF). This molecule is found within the cellular cytoplasm and is one of several molecules that fuse together. Other cytoplasmic molecules, known as SNAPs (soluble NSF attachment proteins), bind to NSF and stabilise the complex. There are receptors for SNAPs both on the cytoplasmic vesicles and the cell outer membrane, such as VAMP (vesicle-associated membrane protein), as well as SNAP-25 and syntaxin, which circulate in plasma. VAMP is also referred to as synaptobrevin.