Hormones are another class of chemicals that affect behavior. Unlike neurotransmitters, hormones are not released by the terminal buttons of a neuron; instead, they are secreted by glands in the endocrine system. So epinephrine (adrenaline) is released by the adrenal gland into the bloodstream as a hormone whereas norepinephrine (noradrenaline) is released by neurons in the brain as a neurotransmitter. Hormones are released...