Arrange the steps involving the actions of a directly acting neurotransmitter in the brain in the correct order.
A. the signal binds a receptor/ion channel
B. the postsynaptic neuron is activated to continue the transmission through the brain 3. ions rush out of/into the neuron
C. vesicles in the presyaptic neuron fuse with the cell membrane
D. the neurotransmitter diffuses across the synapse