Synapses
References
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:
- 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:
- 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:
- 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:
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:
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Lance Hahn (
lance@retina.anatomy.upenn.edu)
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lance@retina.anatomy.upenn.edu)