Nerves function by depolarising and carrying their signal in the form of electricity to the area required. A nerve synapse, occurs at a nerve junction, i.e. a gap between two nerves. The electrical signal is the converted into a chemical one, involving neurotransmitters crossing a synaptic cleft and acting on neurotransmitter receptors. These synapses are therefore potential drug targets.
Presynaptic Membrane Postsynaptic Membrane
(releases neurotransmitter) [synaptic cleft](neurotransmitter receptor)
“A neurotransmitter is one of a class of chemical substances that carry messages between neurons. Typically, a sending neuron releases small amounts of a neurotransmitter, and this activates receptors on the receiving neuron. Receptor activation initiates a series of chemical changes in the receiving neuron, if enough receptors are activated, the receiving neuron may itself become active and send the message along.” i
The neurotransmitter receptor is a protein embedded in a post synaptic neuronal cell membrane. It is activated when bound by a specific neurotransmitter. When activated they may cause a change in the nerve polarisation
There are 2 Classes of Neurotransmitter Receptor
Inotropic (ligand gated ion channel receptor [the neurotransmitter, (the ligand) triggers these types of receptors and in allows ions to flow into or out of the cell]). These receptors are fast (milliseconds), but short acting, examples include GABAA receptors (those affected by Thiopentone), Acetylcholine and Glycine receptors.
Metabotropic are the other receptor class (these are the first step in a signal cascade, [e.g. G protein coupled receptors, that when activated cause a chain of events in the cell.]) These receptors are generally slower (milliseconds to seconds) but longer acting. Examples of metabotropic receptors include GABAB receptors and metabotropic glutamine receptors.
Most inhibitory synapses use GABA or Glycine as a transmitter. GABA inhibitory receptors are found more in the brain and Glycine inhibitory receptors are found more in the spinal cord.