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Human Anatomy and Physiology

How big is a synapse?

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February 27, 2013 10:41AM

It varies by the type of cells involved (for example, a typical synapse from a pyramidal cell in motor cortex to a spinal cord alpha-motorneuron is not the same size as a synapse from that alpha-motorneuron onto a muscle fibre). But as one example, these 1950s papers examining prototypical synapses with an electron microscope (see related links) found that the presynaptic and postsynaptic membranes were separated by about 100-200 angstroms (10-20 nm); they contain synaptic vesicles that are 200-500 angstroms (20-50 nm) in diameter. In Plate 10 of the second of these articles (on invertebrates), the synapse labelled Y has a contact area that is maybe 0.4 micrometres (400 nm) in length in this electron microscope cross-section (so if this were a cut through the middle of a circular synapse, that'd imply a synaptic area of just over one square micrometre - but this is quite variable.