Neurons talk by releasing chemical messengers (neurotransmitters) that fit into receptors on the next cell, like a key in a lock. Most drugs that affect the mind change that conversation in one of two ways: they turn the signal up, or they turn it down.
The same synapse three ways. Watch what happens to the signal that reaches the next neuron.
Receptors come in two basic designs. Acetylcholine uses both, which is why the same messenger can make your bicep contract and your heart slow down.
The receptor is a gate. When the messenger fits, the gate opens and charged particles (ions) rush through.
Fast: about a thousandth of a second.The receptor is a doorbell. When the messenger fits, it sends a helper (a G protein) inside the cell to start a chain reaction.
Slower, about a second, but it lasts longer.Acetylcholine opens a gate on the muscle. Sodium rushes in and the muscle contracts in about a thousandth of a second.
Acetylcholine rings a doorbell. A G protein travels inside the cell and opens a separate potassium channel, so the heart slows down over a second or two.
Pick a neurotransmitter, then a drug. Green drugs are agonists, red drugs are antagonists. Press Space to make the neuron fire.
| Neurotransmitter | Main job | Receptor | Turn it up (agonists) | Turn it down (antagonists) |
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Simplified sketch, not to scale, with everything slowed way down. Real drugs usually act on several receptors at once (alcohol both boosts GABA and dampens glutamate). Cocaine, meth, MDMA, Adderall and Prozac work on the recycling pumps rather than the receptor itself, so they count as indirect agonists. For learning only, not medical advice.