The primary function of a neuron is to communicate information to other cells. The point of communication between two cells is called synapse: at this communication junction, the message-sending neuron is referred to as the presynaptic neuron, the message-receiving neuron is referred to as the postsynaptic neuron. Cells specialized for communication do not touch each other. They are separated by a tiny fluid-filled space called the synaptic gap. At the end of the axon are several small branches called axon terminals. Floating in the fluid of the axon terminals are tiny sacs called synaptic vesicles. The synaptic vessels hold special chemical messengers manufactured by the neuron, called neurotransmitters. When the action potential reaches the axon terminal membrane, so(cid:373)e of the s(cid:455)(cid:374)aptic vesicles (cid:862)dock(cid:863) o(cid:374) the a(cid:454)o(cid:374) ter(cid:373)i(cid:374)al membrane, then release their neurotransmitters into the synaptic gap. These chemical messengers cross the synaptic gap and attach to receptor sites on the dendrites of the receiving or post-synaptic neuron.