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.
How Fast Does A Neurotransmitter Travel Across The Synaptic Cleft? So they turned their attention to the transmission side, measuring the speed of the neurotransmitters’ release. They found that in a functional synaptic connection, the estimated 2,000 to 5,000 molecules of glutamate are usually dumped into the space between the two cells (the synaptic cleft)