Nerve agents cause their physiological symptoms by altering nerve transmissions. A nerve cell sends an electrical impulse down the length of itself until it reaches the end where there is a physical gap, called a synapse, between itself and the next nerve cell or the tissue that it stimulates. At this point the transmitting nerve cell releases a chemical (neurotransmitter) into the synapse where it diffuses across to receptor sites located on the receiving cell which stimulate the desired reaction. Once this is accomplished an enzyme will break the neurotransmitter down to end the stimulation.
The neurotransmitter that nerve agents act upon is acetylcholine. Acetylcholine (Ach) is involved in the stimulation of glands, skeletal muscle, and smooth muscle (gastrointestinal tract) and the enzyme that acts upon it is acetylcholinesterase (Achase). When a nerve agent enters the body, it binds preferentially to Achase so that it cannot degrade the Ach. This means the Ach is able to stimulate the nerve again and again.
Tabun may be exposed through the lungs, eyes, skin and intestinal tract. If one was exposed to realizable field concentrations of Tabun, inhalation would be essentially incapacitating.
The general order of symptoms would be as follows:
First, your nose would begin to run, then your chest would feel constricted. Your vision
would dim as your pupils contracted into pinpoints. You'd begin to drool and sweat
excessively. Then would come nausea and vomiting, intestinal cramps and involuntary
urination or defecation. You'd twitch, jerk, and stagger as you're overcome with convulsions
and possibly coma. Finally, you're breathing would stop as your diaphragm and the muscles
of your chest froze, causing you to die of suffocation.