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Types of Synaptic Contacts

  • 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 image descriptionaxodendritic synapse.
An image showing few dendrites of presynaptic neurons connected to the postsynaptic neuron in different types of synaptic contacts
An image showing few dendrites of presynaptic neurons connected to the postsynaptic neuron in different types of synaptic contacts, the Axodendritic synapse is surrounded by circle
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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 image descriptionaxosomatic synapses.
An image showing few dendrites of presynaptic neurons connected to the postsynaptic neuron in different types of synaptic contacts
An image showing few dendrites of presynaptic neurons connected to the postsynaptic neuron in different types of synaptic contacts, the Axosomatic synapse is surrounded by circle
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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 image descriptionaxoaxonic synapse.
An image showing few dendrites of presynaptic neurons connected to the postsynaptic neuron in different types of synaptic contacts
An image showing few dendrites of presynaptic neurons connected to the postsynaptic neuron in different types of synaptic contacts, Axoaxonic synapse synapse is surrounded by circle
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  • The chemicals released by presynatpic neurons at axodendritic and axosomatic synapses excite or inhibit the dendrites and cell body of the postsynaptic neuron. If image descriptionsufficiently excited, an impulse or image descriptionaction potential will be generated in the axon of the postsynaptic neuron.
  • At axoaxonic synapse, presynaptic neurons image descriptionrelease 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.