Chemical Synapses
Pre-synaptic Classifications
Ribbon Synapse
"....characterized by an electron-dense ribbon or lamella (bar) in the presynaptic process cytoplasm (Sjostrand, 1953; Ladman, 1958; Gray and Pease, 1971). Typically the ribbon is oriented at right angles to the presynaptic membrane and has some depth (~1 micron). It usually sits in or just above an evaginated ridge of the terminal emmbrane..." - Dowling (1987) It is thought that the ribbons help guide the vesicles to the release cites in the cell membrane and that such a synapse is capable of high neurotransmitter release rates.
Examples:
Rod
Cone
Post-synaptic Classifications
Basal Junction
This type of synapse involves an axon which makes contact with the pre-synaptic neuron just beyond a cleft of the dendrite. Typically there are other axons which do make contact within the dendritic cleft.
Examples include:
Diffuse bipolar DB1
Diffuse bipolar DB2
Diffuse bipolar DB3
Invaginating synapse
This type of synapse involves an axon which makes contact with the pre-synaptic neuron within a cleft of the dendrite. Contact is at the deepest point in the cleft.
Examples include:
Invaginating midget bipolar
Partially Invaginating synapse
This type of synapse involves an axon which makes contact with the pre-synaptic neuron within a cleft of the dendrite. Contact is not at the deepest point in the cleft. Typically there are other axons which do make contact at the deepest point within the same cleft.
Examples include:
Off Diffuse bipolar DB1
Off Diffuse bipolar DB2
Electrical Synapses
Gap Junctions
This type of synapse involves a physical break in both the membrane of the axon and the membrane of the dendrite. When these junctions are open, electric potential flows readily between the two cells. Gap junctions may be either bi-directional or uni- directional.
Examples include:
Rod
AII Amacrine
