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7h1
Stimulants and Depressants
Neurotransmitters are molecules with very specific functions. By interacting with
receptors on various postsynaptic membranes, certain actions are stimulated. There are quite
a variety of other molecules that are structurally similar to various neurotransmitters. As you
can imagine, if these molecules interact with your nervous system, there can be peculiar
responses.
Stimulants increase the activity of the nervous system, while depressants have the opposite
effect. Cocaine and amphetamines are similar in structure to norepinephrine, and therefore
have similar effects.
Caffeine is also a stimulant, but its actions are a little different from the previous two
examples. Instead of exciting neurons, it inhibits inhibitory neurons. This causes the same
end result of stimulation of the nervous system.
Barbiturates and Valium mimic GABA, and increase its inhibitory effect.
In addition to acting as stimulants and depressants, there are certain chemicals that play
havoc with the enzymes that would normally break down neurotransmitters at the synapse. If
the enzyme, acetylcholinesterase was destroyed, then the ACh would continuously activate a
postsynaptic membrane. Many organisms (insects, rattlers) have poison or venom that act in
this fashion. Quite effective.
STSE QUESTION Find
an example of any neurotoxin, natural or synthetic and give a brief (less
than 5 sentences) description on how it affects nervous transmission. Be sure to give specific
neurotransmitters and / or enzymes involved.