Is every neurotransmitter receptor an ion channel? This is a rudimentary question--perhaps the answer is well known to biologists, but is every neurotransmitter receptor also an ion channel? For example, NMDAR is a glutamate receptor and cation channel and GABA_A receptors are gated ion channels. Is this true generally? If not, is there a classification of neurotransmitter receptors according to abstract function (e.g. all gated ion channels would form one class, then perhaps there are others)? Thank you in advance! I am a mathematician just getting interested in some biology problems and trying to organize the basic knowledge in this area. I appreciate any insights here!

> is every neurotransmitter receptor also an ion channel?

No.

There are two general types of receptors for neurotransmitters, ligand gated ion channels and receptors that activate second messenger systems, for example, G protein coupled receptors. They are sometimes referred to as ionotropic and metabotropic receptors. This figure from Principles of Neural Science, Ch. 10 illustrates the difference nicely:

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