An emotion involves a subjective experience, physiological response, and expressive response. Emotions elicit physiological changes like increased heart rate and sweating through the sympathetic nervous system. Behavioral responses to emotions include facial expressions and body language, which are important for emotional intelligence and communication. Theories of emotion examine the relationship between physiological, cognitive, and emotional components and whether emotions cause thoughts or physiological responses, or vice versa. Emotions provoke changes in the body like increased respiration and blood flow that prepare the body for action.