talking head: a talker on television who talks directly into the cameras and whose upper body is all that is shown on the screen
speaker: someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)
parasympathetic nervous system: originates in the brain stem and lower part of the spinal cord; opposes physiological effects of the sympathetic nervous system: stimulates digestive secretions; slows the heart; constricts the pupils; dilates blood vessels