The number of identified neurotransmitters has grown significantly as our technical abilities to detect them have improved. Neurotransmitters can be divided into non-peptide and peptide transmitters . Some transmitters act directly by ligand-gated ion channel receptors to change conductances through the postsynaptic membrane . This action is defined as fast or direct synaptic transmission . Other neurotransmitters work through a biochemical pathway, often through a G protein-mediated pathway in the postsynaptic cell , which then produces changes in ion channel conductances.
Many neurotransmitters can mediate fast or slow synaptic transmission depending on the cell type .
Ach may also act through indirect synaptic transmission with a second class of Ach receptors that bind muscarine and are referred to as muscarinic Ach receptors. These receptors are found in cardiac cells and various secretory cells. This causes hyperpolarization and muscle relaxation. The GABA B receptor is a slow indirect receptor. These neurotransmitters are nonpeptide transmitters.