02-04-2009, 05:46 PM
I've always heard it described as a gap. I can't find anything that refers to it as anything but a gap. Many of the sources I've found talk about the concentration of neurotransmitters IN the gap, but they don't say concentration in what. It really does seem like there would have to be SOMETHING, because it's inside the bodies of every organism with a central nervous system, and it doesn't seem like there's any just plain open space, but the synaptic cleft is only about 20 nm thick, so maybe it is just air.
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