MadSci Network: Neuroscience

Re: What's the difference between hormones and neurotransmitters?

Date: Mon Apr 24 09:36:40 2000
Posted By: Terry Hebert, Faculty, Universite de Montreal, Biochemistry, Montréal Heart Institute
Area of science: Neuroscience
ID: 956108887.Ns

	That's a fair question. We'll tackle the simple part first. In North 
America, we refer to the two compounds as epinephrine and norepinephrine 
while in the UK they're referred to as adrenaline and noradrenaline. The 
reason, I suppose has to do with the proprietary names that different drug 
companies gave them on each side of the Atlantic ocean, They are in fact, 
4-[1-hydroxy-2-(methylamino)ethyl]-1,2-benzenediol (adreneline, 
epinephrine) and 4-(2-hydroxy-1-hydroxyethyl)-1,2-benzenediol 
(noradreneline, norepinephrine), respectively.
	Now, for the second part of your question, what's the difference 
between a hormone and a neurotransmitter? Well, the difference is really a 
semantic one, depending on where the molecule is released. A hormone, by 
definition, is a compound produced by an endocrine gland and released into 
the bloodstream where it can find it's target cells at some distance from 
it's actual site of release. A neurotransmitter on the other hand is a 
compound released from a nerve terminal. When an electrical impulse travels 
to the end of a nerve cell, it stimulates the terminal of this cell to 
secrete a chemical signalling molecule at a special junction between nerve 
cells called a synapse. These nerve terminals are in direct apposition with 
their target cells to ensure rapid and specific delivery of the signal. 
This mode of transmission is in general much faster than the endocrine 
transmission I mentioned above. Both target cells possess receptors for the 
signalling molecule and may produce identical biochemical responses, it's 
just a question of the release mechanism that determines whether or not a 
given molecule is a neurotransmitter or a hormone. So, in the case of 
adrenaline, it's a hormone when the adrenal gland releases it into the 
bloodstream and it goes to the heart or the lungs OR it's a 
neurotransmitter when it is released from a stimulated presynaptic nerve 
cell and acts on it's neighbouring postsynaptic cell. Hope this helps...

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