Organophosphate nerve agents like soman, sarin and VX inhibit the production of the enzyme acetylcholinesterase (AChE), this enzyme is used to break down the neurotransmitter acetylcholine (ACh). In the nervous system the neurotransmitter ACh binds to motor receptor neurons that control muscle contractions, when these motor neurons have ACh bound to them this causes the muscle to contract. When the body is ready for the muscle to relax it releases the enzyme AChE, which strips the ACh from the nerve receptors allowing the muscle to relax. However when a nerve agent like sarin is introduced it prevents the cells in the body from producing AChE, without this enzyme the levels of the neurotransmitter ACh continue to build up and stay bound to motor neuron receptors, this causes all of the muscles in the body to enter a prolonged state of contraction and become unable to relax, thus causing death by either asphyxiation (sarin, soman) because the muscles in the diaphragm are unable to function and pull air into the lungs, or death from cardiac arrest from a rapid acting agent (VX) preventing the muscle in the heart from relaxing. The main antidote to organophosphate exposure is a drug called atropine which clears the agents from the cells and stops it from interfering in enzyme production. Prompt administration of atropine is essential, even if exposed to a less than lethal dose as severe nerve and neurological damage can occur even from exposure to minute amounts.
Symptoms of nerve agent exposure are constricted pupils. sweating, muscle twitching at the site of exposure and confusion. This is soon followed by nausea, vomiting, muscle spasms in the extremities, drooling and difficulty breathing, and as loss of muscle control progresses there is a loss of bladder and bowel control. This is followed by severe twitching and jerking and as the fatal stage sets in the person starts to become comatose while their body continues to spasm until death. However unlike how it is often depicted in movies agents like sarin and VX do not cause skin to blister, burn and melt like mustard gas, they cause little to no skin damage.