Features of synapses

• Synapses are unidirectional - they can only pass information in one direction (from the presynaptic neurone to the postsynaptic neurone).
• Summation is a process that allows sufficient concentrations of neurotransmitter to be released in order to trigger a new action potential in the postsynaptic neurone.
• There are two types of summation : spatial summation and temporal summation.
• Spatial summation involves a number of presynaptic neurones firing together to release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone, thereby triggering a new action potential.
• Temporal summation involves a single presynaptic neurone firing many times in a short period of time (i.e. rapidly releasing neurotransmitter chemicals). If the concentration of neurotransmitter exceeds the threshold value, then a new action potential will be stimulated in the postsynaptic neurone.