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Types of Synaptic Contacts

Author: Scott A. Sheffield MS

Last update: Oct 27th, 2022

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In the central nervous system, where most synapses occur, presynaptic neurons can approach and interact with postsynaptic neurons at three locations.

Most presynaptic neurons synapse along the dendritic spines of the postsynaptic neuron. Because of the location, this type of contact is called a axodendritic synapse.

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• Only a few axodendritic synapses are shown here (as examples). However, postsynaptic neurons in the central nervous system typically have thousands of axodendritic synapses.
• Presynaptic neurons also commonly terminate along the cell body (soma) of the postsynaptic neuron. These junctions are termed axosomatic synapses.

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• Synapses can also form between the axon of a presynaptic neuron and the axon of a postsynaptic neuron. This third type of junction is called an axoaxonic synapse.

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• The chemicals released by presynaptic neurons at axodendritic and axosomatic synapses excite or inhibit the dendrites and cell body of the postsynaptic neuron. If sufficiently excited, an impulse or action potential will be generated in the axon of the postsynaptic neuron.

• At axoaxonic synapse, presynaptic neurons release chemicals to alter the activity of the terminal boutons (synaptic knobs) on the postsynaptic neurons. Thus, when an action potential arrives at the terminal boutons, the release of neurotransmitter is either facilitated or inhibited.