Chemical Weapons:
Nerve Agents

You may have read newspaper or magazine articles about the possible use of chemicals during a war or a terrorist attack. Many of these chemicals affect the nervous system and are therefore called nerve agents. Nerve agents are similar to insecticides and they can be deadly if people are exposed to them. Unfortunately, this has already happened. On March 20, 1995, twelve people were killed and over 5,000 were injured when a nerve gas called "sarin" was released in the Tokyo subway system. People may have also been exposed to nerve agents during the conflict ("Gulf War") in the Middle East. It is possible that many countries have access to these dangerous weapons and future human exposure to these chemicals is possible.

History

mask nopest Most nerve agents belong to a group of chemicals called "organophosphates". The first of these chemicals was made in 1854 and was originally developed to be used to control insects and save crops. The first nerve agent (called "Tabun" or "GA") for military use was made in Germany in 1936. Another nerve agent, "sarin" or "GB," was made in 1938 and "Soman" or "GD" was made in 1944. It appears that these nerve agents were not used by the Germans during World War II. However, it has been estimated that the Germans had stockpiles of tons of both Tabun and Sarin. The United States and Russia continued producing and stockpiling these nerve agents after the War. In the 1950s another nerve agent, "VX," was produced in England.

NameFirst Made
(Year)
Lethal Dose
Breathing (mg*min/m3)
Lethal Dose
Skin (mg)
Tabun (GA)1936150-4001,000-1,700
Sarin (GB)193875-1001,000-1,700
Soman (GD)194435-5050-100
VX1952106-10
There are several less common nerve agents: GE, GF, VE, VG and VM

Breathing a lethal dose of these chemical can kill in 15 minutes; a lethal dose on the skin can kill in only 1-2 minutes!! To get an idea of how deadly these chemicals are, do the math.

1 kilogram = 1,000 gm = 2.2 lbs
   1 gm  =   1,000 mg = 0.0022 lbs
   10 mg = 0.000022 lbs
10 mg (0.000022 lbs) is not much more than a single grain of rice!!

Nerve agents are clear and colorless and may have no odor or a faint, sweetish smell. They are all extremely dangerous and they can enter the body through the air or on contact with the skin. They can be released using bombs, missiles, spray tanks, rockets and land mines. VX is the most deadly and Tabun is the least deadly (although still very hazardous). Nerve agents are more dense than air so they are especially dangerous to people in low areas.


Method of Action

Acetylcholine is a common neurotransmitter found in the central and peripheral nervous system. When acetylcholine is released from an axon terminal, it moves across the synaptic cleft to bind to a receptor on the other side of the synapse (on the post-synaptic membrane). In the peripheral nervous system, acetylcholine is located at the "neuromuscular junction" where it acts to control muscular contraction. Acetylcholine is also used in the autonomic nervous system. The action of acetylcholine is stopped by an enzyme called "acetylcholinesterase" (AChE).

Nerve agents bind to part of the AChE molecule. This makes the AChE inactive and blocks the action of AChE. Therefore,

  1. there is no way to stop the action of acetylcholine
  2. acetylcholine builds up at the synapse.
  3. acetylcholine continues to act.

The Acetylcholine Synapse

Normal Transmission of Acetylcholine

ACh = Acetylcholine
E = Acetylcholinesterase

  1. ACh is released at the axon terminal.
  2. ACh crosses the synaptic cleft.
  3. ACh binds with a receptor on the post-synaptic membrane.
  4. AChE (E) stops the action of ACh.
Transmission with Nerve Agent Poisoning

ACh = Acetylcholine
E = Acetylcholinesterase
NA = Nerve Agent

  1. ACh is released at the axon terminal.
  2. ACh crosses the synaptic cleft.
  3. ACh binds with a receptor on the post-synaptic membrane.
  4. Nerve agents (NA) block the ability of AChE to stop the action of ACh.
  5. ACh continues to work and more ACh builds up in the synapse.

Symptoms of Nerve Agent Poisoning

Nerve agents attack all synapses that use acetylcholine as a neurotransmitter...this means both the central and peripheral nervous systems are affected. Symptoms of nerve agent poisoning include:

Neuromuscular EffectsAutonomic Nervous
System Effects
Central Nervous
System Effects
  • Twitching
  • Weakness
  • Paralysis
  • Respiratory failure
  • Reduced Vision
  • Small pupil size
  • Drooling
  • Sweating
  • Diarrhea
  • Nausea
  • Abdominal pain
  • Vomiting
  • Headache
  • Convulsions
  • Coma
  • Respiratory arrest
  • Confusion
  • Slurred speech
  • Depression
  • Respiratory depression

Treatment for Nerve Agent Exposure

Immediate treatment of person who has been exposed to a nerve agent exposure includes a complete washing of the eyes and skin with water. A diluted (0.5%) bleach solution should also be applied to the skin if possible.

Two drugs, atropine and pralidoxime chloride, have been used as antidotes for nerve agent poisoning. Atropine works by blocking one type of acetylcholine receptor so that the acetylcholine that is already in the synapse cannot work. Pralidoxime works by blocking the binding of the nerve agent to the AChE. Both of these drugs were issued to US troops during the Persian Gulf War in the form of an antidote kit called the Mark I. Diazepam (Valium) may be used to reduce convulsions and seizures brought on by exposure to nerve agents.

Effects of Atropine

Effect of Atropine on the Transmission of Acetylcholine in the presence of a nerve agent

ACh = Acetylcholine
E = Acetylcholinesterase

  1. ACh is released at the axon terminal.
  2. ACh crosses the synaptic cleft.
  3. ACh binds with a receptor on the post-synaptic membrane.
  4. Nerve agents (NA) block the ability of AChE to stop the action of ACh.
  5. Atropine blocks the receptor so that ACh cannot work. Note that there is NO direct effect on the nerve agent or AChE.

BACK TO: Exploring the Nervous System Table of Contents

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