Stopping the Signal

Once a postsynaptic neurone has been stimulated by the secretion of neurotransmitter molecules and the binding of these molecules to receptors, the stimulus must be turned off.

 

Neurotransmitter molecules bind to their receptors for about 1 millisecond and then dissociate or breakaway. When lots of neurotransmitter molecules are being released, one molecule will quickly be replaced by another so that the postsynaptic neurone is stimulated again.

So the signal could be ended by stopping further neurotransmitter molecules from being secreted and by removing any neurotransmitter molecules within the synaptic gap. Neurotransmitter secretion is stopped when action potentials cease in the presynaptic neurone.

The removal of neurotransmitter molecules from the synaptic gap is achieved in three ways:

Diffusion

Reuptake

Degradation

 
Consider the effect of these mechanisms on the concentration of transmitter molecules in the synaptic cleft and the implications of this.