There are two types of removal: Re-uptake – the neurotransmitter is reabsorbed back into the presynaptic neuron and restored inside a vesicle ready to be used again. For example, noradrenaline.

However, a series of weak stimuli can combine, increasing the amount of neurotransmitter that is released. This results in enough neurotransmitter being diffused across the synaptic cleft to ...