|MadSci Network: General Biology|
Those are all really good questions (after all, you asked 4). I will try to break them down by alcohol and caffeine and see if I can answer them a bit.
Let's start with alcohol:
What we commonly call alcohol is actually ethanol (or ethyl alcohol), which is primarily important because "wood alcohol," or methanol, is a potent poison. [As my high school chemistry teacher once said, "Methanol will kill you in hours; ethanol takes a number of years."]
The exact mode of action of alcohol is not completely understood. We do know that alcohol has some anaesthetic properties, and that may result from it's directly interfering with the binding of certain neurotransmitters, especially acetylcholine. However, it is most likely acetaldehyde (or ethanal), a primary metabolite of ethanol, that causes most of the problems. Acetaldehyde is known to react with dopamine yielding salsolinol and also to react with tryptamine producing tetrahydroharman. Both of those products have psychotropic activity. Since dopamine is also a precursor to noradrenalin (which acts in motor pathways), dopamine depletion may also be involved. Lastly, often forgotten is the fact that ethanol is a desiccating agent; that means that it removes water from systems. Many of the unpleasant effects of alcohol are likely to come from the fact that various parts of the body are dealing with dehydration.
As for caffeine, it's likely mode of action in the nervous system is to modulate neurotransmission via alteration of intracellular calcium levels. When caffeine passes through a cell membrane (which it is hydrophobic enough to do), it binds to a set of receptors on the internal calcium stores [namely places like the endoplasmic reticulum]. By binding to those receptors, it causes a release of the calcium within those stores, and thus the increase in intracellular calcium levels.
Now, there are a number of neuromodulatory events that can arise from such an increase in intracellular calcium:
For further reading, I recommend Murder, Magic, and Medicine, by John Mann (ISBN:0-19-855854-6), which is a good primer on many of the effects of natural products. I also consulted several references from PubMed, after searching for & quot;caffeine AND calcium AND reticulum AND neuron".
Good luck with your studies. I hope this helps.
Try the links in the MadSci Library for more information on General Biology.