Final answer:
Messages from the brain that have a chemical origin, like serotonin, are called neurotransmitters, which facilitate chemical synapses between neurons and other cells.
Step-by-step explanation:
The messages from the brain that have a chemical origin called serotonin, which are not strictly electrical, are known as neurotransmitters. Neurotransmitters are endogenous chemicals that transmit signals across a chemical synapse, from one neuron to another neuron, muscle cell, or gland cell. Serotonin is one such neurotransmitter that is derived from tryptophan and is essential for the serotonergic system of the brain, influencing mood and other functions.