What is the synaptic cleft?

• A. The space within a neuron where neurotransmitters are produced
• B. The small space between the end of one neuron and the beginning of the next across which neurotransmitters move to continue the electrical impulse
• C. The gap in the blood-brain barrier
• D. The junction between a neuron and a supporting cell

Answer: (B)

The synaptic cleft is the tiny gap that separates the end of one neuron (the presynaptic terminal) from the start of the next cell (which can be another neuron or a muscle cell). When an electrical impulse reaches the presynaptic terminal, neurotransmitters are released into this space and diffuse across it to bind receptors on the postsynaptic membrane. This chemical signaling across the cleft then propagates or modulates the signal in the receiving cell, continuing the communication process.

It’s not the space where neurotransmitters are produced—that happens inside the neuron’s cell body and terminals. It’s not a gap in the blood-brain barrier, which is a barrier between blood vessels and brain tissue. It’s also not the junction between a neuron and a supporting glial cell; the cleft is specifically the space where chemical transmission occurs between neurons (or between a neuron and a muscle cell).