chemical synapse

A chemical synapse is the tiny junction where one neuron passes its message to the next cell — but instead of the two cells touching, they are separated by a microscopic gap. Picture two people standing on opposite banks of a very narrow stream: they cannot hand the note across directly, so one of them folds it into a paper boat and floats it over. In a chemical synapse, the message is carried across that gap not by electricity jumping the divide, but by little packets of chemical messengers, called neurotransmitters, that the sending cell squirts out and the receiving cell catches.

Here is how it works. When an electrical signal arrives at the end of the sending neuron, it triggers tiny bubbles full of neurotransmitter to fuse with the cell's outer wall and dump their contents into the gap, which is called the synaptic cleft. These chemical messengers drift across and lock onto matching catcher molecules, called receptors, studded on the surface of the receiving cell — like keys fitting into keyholes. That binding nudges the receiving cell to either fire its own signal or hold back. This chemical relay is slightly slower than a direct electrical jump, but it gives the brain enormous flexibility: the strength of the connection can be turned up or down, which is the physical basis of how we learn and remember.