Glossary
Synaptic Cleft
What is the synaptic cleft?
The synaptic cleft, or synaptic gap, is the narrow space between the releasing and receiving cells at a chemical synapse. The receiving cell may be another neuron or a muscle cell.
The cleft is one part of a chemical synapse. The synapse also includes the releasing terminal and the receiving membrane; the two terms do not mean the same thing.
How signals cross the gap
The presynaptic terminal stores neurotransmitter in vesicles. An arriving action potential can trigger its release. Transmitter crosses the cleft and binds to receptors on the postsynaptic membrane. The effect depends on the transmitter and receptor involved.
Reuptake and breakdown
Transmitter does not remain indefinitely at the release site. It can be taken up by neurons or glia, broken down by enzymes, or diffuse away. Different transmitters use these routes to different degrees.
Why it matters
Release, receptor action, and clearance all affect communication between cells. Selective serotonin reuptake inhibitors (SSRIs) provide a concrete example. Sertraline inhibits neuronal reuptake of serotonin: it reduces the uptake process that removes released serotonin from the space outside cells. This changes serotonergic signaling. A clinical benefit from a drug does not by itself establish that a pre-existing “chemical imbalance” was measured and corrected.