Neurotransmitters and receptors
Neurotransmitters: Conventional and unconventional
Small molecule neurotransmitters
- The amino acid neurotransmitters glutamate, GABA (γ-aminobutyric acid), and glycine. All of these are amino acids, though GABA is not an amino acid that's found in proteins.
- The biogenic amines dopamine, norepinephrine, epinephrine, serotonin, and histamine, which are made from amino acid precursors.
- The purinergic neurotransmitters ATP and adenosine, which are nucleotides and nucleosides.
- Acetylcholine, which does not fit into any of the other structural categories, but is a key neurotransmitter at neuromuscular junctions (where nerves connect to muscles), as well as certain other synapses.
A neurotransmitter’s effects depend on its receptor
- Glutamate is the main excitatory transmitter in the central nervous system.
- GABA is the main inhibitory neurotransmitter in the adult vertebrate brain.
- Glycine is the main inhibitory neurotransmitter in the spinal cord.
- The acetylcholine receptors in skeletal muscle cells are called nicotinic acetylcholine receptors. They are ion channels that open in response to acetylcholine binding, causing depolarization of the target cell.
- The acetylcholine receptors in heart muscle cells are called muscarinic acetylcholine receptors. They are not ion channels, but trigger signaling pathways in the target cell that inhibit firing of an action potential.
Types of neurotransmitter receptors
- Ligand-activated ion channels: These receptors are membrane-spanning ion channel proteins that open directly in response to ligand binding.
- Metabotropic receptors: These receptors are not themselves ion channels. Neurotransmitter binding triggers a signaling pathway, which may indirectly open or close channels (or have some other effect entirely).
Ligand-activated ion channels
Conventional neurotransmitters and their receptor types
|Neurotransmitter||Ligand-activated ion channel receptor(s)?||Metabotropic receptor(s)?|
|Acetylcholine||Yes (excitatory )||Yes|