Definition
A receptor is a protein, usually embedded in a cell's membrane, that detects a specific signaling molecule and triggers a response inside the cell. In the brain, receptors sit on the receiving side of the synapse, waiting for neurotransmitters to arrive. A signal means nothing until a receptor reads it.
The match between messenger and receptor is specific, often described as a lock-and-key fit. A dopamine molecule binds a dopamine receptor; the wrong molecule has no effect. This specificity is what gives the brain's chemistry its precision.
Why it matters
How it works
When a neurotransmitter binds its receptor, the receptor changes shape and sets off events inside the receiving cell — opening an ion channel directly, or launching a slower chemical cascade. Either way, the receptor translates an outside chemical signal into a change in the cell's state.
Receptors are not fixed. A cell flooded with a neurotransmitter will reduce its receptor count to dampen the signal; a cell starved of one will add receptors to grow more sensitive. This dynamic regulation explains tolerance, sensitization, and why the same neurotransmitter level produces different effects in different people. Behave returns to receptors to show how genes shape behavior — many gene variants act by altering receptor structure or number.