synaptic gap

Is Synaptic Cleft Narrow? “Synapses are very small. This narrow gap of extracellular space is approximately 20-40 nanometers (nm) wide. For an idea of scale, one inch is about 25.4 million nm long. What is the size of a synapse? How big is a synapse? Synapses are tiny—you cannot see them with the naked eye.