Definition
A synapse is the tiny gap where one neuron communicates with the next. Neurons do not physically touch; the axon terminal of one cell sits a minuscule distance from the dendrite of another, and the signal must cross that space. The synapse is where the action of the brain — learning, memory, mood, behavior — is actually negotiated.
Crossing the gap is a chemical event. The electrical impulse arriving at the sending side is converted into a chemical message that drifts across the synapse and is detected on the receiving side.
Why it matters
How it works
When an action potential reaches the axon terminal, it triggers the release of neurotransmitter molecules into the synaptic gap. Those molecules drift across and bind to receptors on the receiving neuron, nudging it toward or away from firing. The leftover transmitter is then cleared away — reabsorbed or broken down — so the synapse is ready for the next signal.
The crucial property is plasticity. A synapse that is repeatedly used grows stronger, and a neglected one weakens. This adjustable strength, summed across trillions of synapses, is the physical basis of learning, memory, and the lasting changes experience leaves in the brain.