1 2 3 4 5 6

		a. Neurotransmitter release When the action potential arrives at the axon terminus, it causes voltage-gated calcium channelsto open. The influx of Ca++ ions causes the neurotransmitter-contining vesicles to fuse with the plasma membrane, releasing their contentsinto the synaptic cleft.
				Presynaptic cell
						Postsynaptic cell
		b. Receptor in postsynaptic membrane The neurotransmitter diffuses across the synaptic cleft and binds to a receptorin the membrane of the postsynaptic cell. This can be either the dendrite of another neuron or the motor end-plate of a muscle cell. c. Fast vs slow In fastchemical synapses, the neurotransmitter receptor is directly coupled to an ion channel. When the neurotransmitter binds, the channel opens. These are known as chemically gated or ligand gated channels. In slowchemical synapses, the binding of the neurotransmitter to its receptor triggers a signal transduction cascadeinvolving G-proteins, which eventually opens the ion channel.