They ensure unidirectional transmission - Nerve impulses can also pass from the pre-synaptic neurone to the post-synaptic neurone. This is due to the neurotransmitter being made in the pre-synaptic membrane and the neurotransmitter receptors being present in the membrane of the post-synaptic neurone.They prevent overstimulation of effectors - Too many impulses passing along the same neurone in a short period of time will exhaust the supply of neurotransmitter more quickly than it can be built up and the synapses will fatigue Could also have said integration or allows nerve impulses to pass from neurone to neurone to allow nervous communication to continue.