[Braddock]

  OK, Couldnt find anywhere on the web that directly addresses this question, So I thought why not ask here. Ill start by prefacing with this, Nerve agents are a form of chemical weapons. I know how they work, But what Ive always wondered, Is how do they work so effectively? The same is true for certain venoms of snakes. How is it, That such a small dose can have such a devestating affect ona person? If you drop one tablespoon of gasoline in a 50 gallon tank of water, The sheer volume of the water is going to dilute the gasoline to such a point, That its going to have a very nominal effect on contamination of the water. How is that a snake bite or nerve agent in such a smal dose can affect your entire body? Wouldnt the affect be fairly localized?If you get bit on the foot, How is there enough of the chemicals in the poison to make it all the way to your brain or heart without most of it being absorbed by your body as it travels there?

[AWK]

Nerve gases are not so toxic. Their LD50 is a few miligrams.
may be these links hepl:
http://en.wikipedia.org/wiki/Chemical_weapon
http://www.emedicine.com/EMERG/topic852.htm
http://www.thewednesdayreport.com/twr/vx.htm
 

[constant thinker]

Ok look at this analogy.

You have morphine which takes effect relatively fast when administered intravenously. Heroin though when administered the same way takes effect faster. Both drugs are in the same class the only difference is a that heroin is a slightly modified structure of morphine.

What I'm getting to is that depending on the compounds structure it can more effectively stimulate (speed up) or depress (slow down) a receptors activity. This is called its efficacy. Heroin has a greater efficacy than morphine because its structure allows it to be more fat soluble and enter the brain a lot faster. Solubility isn't the only variable though. What receptors the toxin will affect can play a role. The more vital the receptor that is effected the more likely it is to cause serious harm.

[mike]

More than likely the molecules will have the perfect size or shape to do the job of poisoning the body. Your analogy doesn't really work because you are thinking only in terms of quantity and not "quality". Receptors in the human body are very specifically shaped and sized so that only equally specifically shaped and sized molecules will interact with them.

In saying this however, you are right that there are different lethal doses for different compounds, as well as exposure limits for the compounds. Maybe someone who knows a little more about the human body than myself can expand on this.

constant thinker: does heroin really enter the brain?

[Braddock]

  Sooo, Do the compounds, Say in a nerve agent, affect a receptor, then move to the next one then the next one and so forth?  

[mike]

I don't know exactly, and I presume it would depend on what nerve agent you are talking about. However, if a receptor is irreversibly bound to a "poison" compounds it won't perform its job, whether that be transferring nerve signals, relesing a hormone, carrying oxygen etc etc, so it doesn't really have to go from site to site as you are picturing. Think of it more as a "bottle-neck" kind of effect where the compound is stuck in the neck of the bottle impeding the "flow" of whatever is supposed to be coming in or going out, in this analogy you only need a small change to cause a huge catastrophic result. Or on the other hand imagine a dam with a a steady flow of water coming out of it, if a "poison" compound were to come along and bust open the valve there would be a catastrophic release of water (not sure if you get what I mean or not from these analogies). But I presume that a small amount of a compound could trigger a land slide type of effect in the human body. Remember that it is more than likely the way the body reacts to the compound that will cause the problem.

What do others think? Is this too simplistic a way to picture how a small amount of something can cause or trigger a large effect?

[constant thinker]

constant thinker: does heroin really enter the brain?

Heroin acts on the opiate receptors and it's fat soluble. There are many opiate receptors in the brain, so why would heroin not enter the brain. The specific opiate receptors it primarily acts on are in highest concentration through the brain and spinal chord I believe.

I realized that my analogy was kind of weak though, but I couldn't think of anything better.

[mike]

I realized that my analogy was kind of weak though, but I couldn't think of anything better.

I wasn't questioning your analogy at all I was just interested to learn that heroin crosses the blood brain barrier. I learn something new everyday  

[Borek]

Scientific American article

[mike]

Scientific American article

Interesting articles ----> the "related article" is interesting too.

[Braddock]

  Ezxcellent article, Thanx.

[jdurg]

I wasn't questioning your analogy at all I was just interested to learn that heroin crosses the blood brain barrier. I learn something new everyday  

Yup.  In a sense, all of the opiates act in the same way on the brain.  It's just their ability to get "inside" the brain that causes the differences in the strength.  Heroin is readily able to cross the blood-brain barrier so it is able to "do its work" on the brain before it gets metabolized by the body.  Codeine, Morphine, and some of the other opiates aren't able to cross the blood-brain barrier as easily and they get metabolized a bit before they get a chance to act on the brain.  With all drugs and toxins, it's their ability to get to their desired destination that plays a role in how readily toxic/effective they are.