itary gland).Hormone, from Greek hormon = to set in motion, stir up. In physiol-
ogy, hormones refer to chemicals released by endocrine glands into
the blood circulation, whereupon they mediate effects throughout
the body.Playing an important role in the autonomic neural component of
emotion is the vagus nerve (cranial nerve 10), consisting of neural
connections between the brain and a large region of the core of the
body (Latin vagus = wandering). Included in this circuitry is the
parasympathetic innervation of the body’s core—the heart, lungs, di-
gestive system, and other body organs. Parasympathetic input to the
heart functions to decrease heart rate. This is what Otto Loewi was
investigating when he discovered chemical neurotransmission (see
Chapter 6).