Classification of synapse
- Morphological classification:
- Axodendritic
- Axosomatic
- Axoaxonal
- Functional classification:
- Excitatory
- Inhibitory
Synaptic glomeruli
- Several neurons take part in forming complex synapses encapsulated by neuroglial cells
Chemical synapse types
- Axosecretory
- Axon terminal secretes directly into bloodstream (e.g., hypothalamus)
- Axodendritic
- Axon terminal ends on dendritic spines or shaft (type I excitatory synapse)
- Axoaxonic
- Axon terminal secretes onto another axon
- Axoextracellular
- Axon with no connection secretes into extracellular fluid
- Axosomatic
- Axon terminal ends on cell soma (type II inhibitory synapse, e.g., basket cell onto Purkinje cell)
- Axosynaptic
- Axon terminal ends on presynaptic terminal of another axon
Electrical synapses
- Only represent a small minority of synapses
- e.g., some neuroendocrine cells in hypothalamus
- Structure
- Closely apposed pre and post-synaptic membranes connected by a gap junction.
- The connexon is a proteinaceous cylinder with a hydrophilic channel and is the structural unit of the gap junction.
- Direct electrical communication between cells occurs through gap junctions and may be important in the pathogenesis of diseases of the nervous system including epilepsy
- These junctions contain aligned paired channels so that each paired channel forms a pore (larger than those observed in ligand-gated channels) and allows for the bidirectional transmission.
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