The axon, which is protected by a myelin sheath, transmits electrical impulses from the soma to other neurons, muscles, and glands. The nervous system depends on neurotransmitters that trigger signal transmission that leads to emotions and motions. Notably, endorphins and norepinephrine control emotions and alertness respectively. Gamma-aminobutyric acid such as serotonin regulates moods, hunger, and sleep. Acetylcholine and dopamine have both exciting and inhibitory properties. The former triggers muscle action and memory while the latter is important in learning, movement, and pleasurable emotions. Excess dopamine has a link to addictive and impulsive behavior, as well as, schizophrenia. Hormones are chemical transmitters in the endocrine system, and exert action on the brain, as well as, other organs. Notably, hormones regulate moods, arousal, circadian rhythm, metabolism, growth, immune system, and sexual reproduction. Unlike the neurotransmitter, the transmission of messages through hormones is slower. The transmission involves secretion of hormones by glands that enter the bloodstream and eventually reach the brain. It is noteworthy that the hormonal effect is long lasting. The most important gland in the brain is the pituitary that release growth hormone and oxytocin, which play a role in social bonding. In summary, the communication between the brain and peripheral organs involves nervous and endocrine systems.Franz Joseph Gall, a German physician, perceived that a link existed between personality and skull morphology.