Were there chemical soups in the brain, or sparks? The answer turned out to be: both. Neurons send electrical signals down the long cables of their axons, which connect to other neurons via small synaptic gaps. When the electrical charge reaches the synapse, it releases a chemical messenger—a neurotransmitter, like dopamine or serotonin—that floats across to the receiving neuron and ultimately triggers another electrical charge, which travels out to other neurons in the brain.
