Whether a synapse is inhibitory or excitatory is determined by the ion-channels present in the postsynaptic neurone. At an inhibitory synapse channels that let in anions, such as chloride ions, or channels that let out cations, such as potassium ions, are present.
An inhibitory synapse prevents firing of an action potential in the postsynaptic neurone. It does this by causing an IPSP (inhibitory postsynaptic potential) at the postsynaptic neurone by releasing inhibitory neurotransmitters. Once the inhibitory neurotransmitter is released and bound to the neurotransmitter receptors on the postsynaptic neurones these channels are opened and so positive charges are either lost or negative charges are gained and so the membrane potential drops causing hyperpolarisation. threshold value (-55mV) is not reached and so action potential is not fired.
Inhibitory synapses are very important. It has been shown that toxins that prevent inhibitory neurotransmitters from working, can cause adverse effects. For example, strychnine binds to inhibitory glycine receptors and blocks its inhibitory function. This results in muscle spasms, convulsions and death .
- ↑ Alberts B, Johnson A, Lewis J, Raff M, Roberts K and Walter P. (2008) Molecular Biology of the Cell, fifth edition, New York and Abingdon: Garland Science, Taylor and Francis Group.