"Normally, When a neuron fires, it will release a neurotransmitter through its axons, the dendrites on the other side of the synapse will react to the presence of the neurotransmitter, and the message will have been delivered. After the message has been delivered, the neuron sending the message will reabsorb the neurotransmitter it originally emitted so that you don't have that chemical floating around in your brain, activating neurons it didn't intend to activate. The process of reabsorption of the neurotransmitter is known as reuptake. Reuptake is like garbage collection for your brain! "