The space between the presynaptic and postsynaptic membranes is approximately how wide?

The space between the presynaptic and postsynaptic membranes is approximately how wide?

• A. 5-10 nanometers
• B. 20-40 nanometers
• C. 80-100 nanometers
• D. 1-2 micrometers

Answer: (B)

In chemical synapses, the presynaptic and postsynaptic membranes sit separated by a tiny gap called the synaptic cleft. The width of this cleft is on the order of tens of nanometers, typically about 20–40 nanometers. This narrow distance lets neurotransmitters released from vesicles diffuse across quickly to bind receptors on the postsynaptic membrane, producing a rapid response. If the space were much smaller, signaling proteins and the precise alignment needed for transmission could be strained; if it were much larger, diffusion would slow and the signal would weaken. Electron microscopy measurements consistently place the synaptic cleft in the 20–40 nm range, making this the best-fit answer.

In chemical synapses, the presynaptic and postsynaptic membranes sit separated by a tiny gap called the synaptic cleft. The width of this cleft is on the order of tens of nanometers, typically about 20–40 nanometers. This narrow distance lets neurotransmitters released from vesicles diffuse across quickly to bind receptors on the postsynaptic membrane, producing a rapid response. If the space were much smaller, signaling proteins and the precise alignment needed for transmission could be strained; if it were much larger, diffusion would slow and the signal would weaken. Electron microscopy measurements consistently place the synaptic cleft in the 20–40 nm range, making this the best-fit answer.