What binds neurotransmitters in the postsynaptic cell membrane to alter excitability?

Neurotransmitter receptors are specialized proteins located on the postsynaptic cell membrane that bind to neurotransmitters released from the presynaptic neuron during synaptic transmission. When a neurotransmitter, such as dopamine or serotonin, binds to these receptors, it triggers a conformational change in the receptor that initiates a cascade of cellular events, ultimately leading to changes in the excitability of the postsynaptic neuron.

This binding can lead to the opening or closing of ion channels, which directly influences the flow of ions into or out of the cell. This change in ion permeability can result in the depolarization or hyperpolarization of the neuron, thus altering its overall excitability and influence on action potential firing. Each type of neurotransmitter receptor is specific to certain neurotransmitters, allowing for finely tuned communication between neurons.

The other options do not play a direct role in this specific binding process. Enzymes are involved in neurotransmitter synthesis or degradation, synapses refer to the structures where neurotransmission occurs, and neurons are the cells that transmit signals, but it is the neurotransmitter receptors that specifically facilitate the binding of neurotransmitters to effect changes in cell excitability.