Final answer:
Neurotransmitters are classified as excitatory or inhibitory based on their effects on the postsynaptic neuron's membrane potential, which is mediated through the binding to specific receptors that control ion channels or activate G-protein-coupled receptors, ultimately determining the likelihood of a neuron firing an action potential.
Step-by-step explanation:
Neurotransmitters are classified as either excitatory or inhibitory based on their effect on the postsynaptic neuron. Excitatory neurotransmitters, like glutamate and acetylcholine, bind to receptors and typically cause depolarization (an increase in the membrane potential) leading to an excitatory postsynaptic potential (EPSP), which increases the likelihood that the neuron will fire an action potential. On the other hand, inhibitory neurotransmitters, like GABA and glycine, cause hyperpolarization (a decrease in the membrane potential), creating an inhibitory postsynaptic potential (IPSP), which decreases the likelihood that a neuron will fire an action potential.
This process is mediated through the binding of neurotransmitters to specific receptors on the postsynaptic membrane, leading to the opening of ionotropic (ligand-gated ion channels) or the activation of metabotropic (G-protein-coupled) receptors. These receptors determine the effect of the neurotransmitter on the postsynaptic neuron, which may vary across different target cells. The final effect of a neurotransmitter depends on the receptor subtype it activates and the resulting intracellular changes.