The brain is made up of structures alled neurons, which acts processed and sends information through electircal impulses. Because neurons do not touch eachother, hese electrical impulses are sent through a gap between neurons called the synapse, meaning the signal has to jump between neurons. The signals that make this journey are chemicals called neurotransmitters, which control different aspects of behaviour (e.g serotonin in mood).
Synaptic transmission happens in a series of stages. First, an electrical impulse stimulates the axon (the end) of the first neuron, which is known as the transmitting neuron as it is the first in a sequence. The electricity causes neurotransmitters to be released. These then diffuse, or jump across the synaptic gap to the following neuron. There are molecules in the start (dendrite) of the second neuron that bind to specific neurotransmitters, like a key fitting into a lock. These molecules are called receptors and trigger the second neuron to begin the process again, causing another electrical impulse to release more serotonin. The neurotransmitter is then reabsorbed to be used again later. This is known as reuptake and allows the brain to recycle the chemicals it uses.