A heightened state of physical responsiveness, involving neural, hormonal, visceral and muscular changes resulting from messages sent throughout the autonomic nervous system(the portion of the peripheral nervous system that sends communications between the central nervous system and the internal organs and glands) and the endocrine system (the hormone system – the body’s chemical messenger system, including the endocrine glands: pituitary, thyroid, parathyroid, adrenals, pancreas, ovaries and testes).