Synaptic Transmission and Reuptake

Two neurons never touch. Between the axon terminal of one and the dendrite of the next sits a tiny gap called the synapse, and nothing electrical ever crosses it. Here is the actual sequence: an electrical signal travels down the sending neuron and reaches the axon terminal, where it triggers tiny sacs called vesicles to dump neurotransmitter molecules into the synapse. Those molecules diffuse across the gap and bind to receptor sites shaped to fit them, like a key fitting a lock, on the receiving neuron's dendrite. That binding can excite the next neuron toward firing or inhibit it from firing. The signal has gone from electrical to chemical and back to electrical, never jumping anything.

Once the message is delivered, the synapse needs to be cleared, or leftover neurotransmitter would keep stimulating the receiving neuron and blur every signal into the next. Reuptake handles this: transporter proteins on the sending neuron's membrane reabsorb the used neurotransmitter back into the axon terminal, where it gets repackaged for reuse or broken down. This is also fast, so the synapse is clean within milliseconds and ready for the next pulse.

This cleanup step is exactly where many psychiatric drugs act. A reuptake inhibitor blocks those transporter proteins, so neurotransmitter lingers in the synapse and keeps stimulating receptors longer than it normally would. That is the mechanism behind drugs like SSRIs, which block the reuptake of serotonin specifically, leaving more serotonin active in the synapse over time to ease depression symptoms.