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Each axon terminal contains thousands of membrane-bound sacs called vesicles, which in turn contain thousands of neurotransmitter molecules each. Neurotransmitters are chemical messengers which relay, amplify and modulate signals between neurons and other cells.
The transmission of information is accomplished in two ways: 1  Electrically: the neuron is directly adjacent to other neurons. 2  Chemically: there is a space (the synaptic cleft) between the axon terminus and the adjacent neuron.As the action potential reaches the end of the axon, a chemical is released that travels across the synaptic cleft to the next neuron to alter its electric potential.With very few exceptions, mammalian organisms use chemical means to transmit information. The vesicle merges with the presynaptic membrane. 2  The presynaptic membrane and vesicle now forms a continuous membrane, so that the neurotransmitter is released into the synaptic cleft. 3  This process is called exocytosis.