As synapse is defined as a junction between two nerve cells consisting of a gap across which impulses pass by diffusion of a neurotransmitter. The neurotransmitter is critical in determining whether a chemical synapse is a excitatory or inhibitory. Neurotransmitters released at excitatory synapse cause the postsynaptic membrane to depolarise. All neurotransmitters cause an opening of ligand-gated sodium ion channels. The excitatory neurotransmitters create a local increase of permeability of sodium ion channels. As a result in more sodium ions flow in which leads to a local depolarisation that's known as an excitatory postsynaptic potential (EPSP). This increases the likelihood of post synaptic cell to fire an action potential.
An important example is the Glutamatergic synapse. Glutamate is a small amino acid neurotransmitter and is the main excitatory neurotransmitter in the central nervous system. It binds to a number of inotropic receptors such as the AMPA receptor, and the NMDA recetor. This causes an influx of cations into the postsynaptic cell, hence depolarising the cell, which makes an action potential more possible. Note that many closely timed EPSP are required to generate an action potential in the axon of the postsynaptic neurone.
- ↑ Alberts, B., Bray, D., Hopkin, K., Johnson, A., Lewis, J., Raff, M., Walter, P. Essential Cell Biology 4th Edition. New York: Garland Science. (2014).