Emotions are complex. According to some theories, they are a state of feeling that results in physical and psychological changes that influence our behavior. The physiology of emotion is closely linked to arousal of the nervous system with various states and strengths of arousal relating, apparently, to particular emotions. Emotion is also linked to behavioral tendency. Extroverted people are more likely to be social and express their emotions, while introverted people are more likely to be more socially withdrawn and conceal their emotions. Emotion is often the driving force behind motivation, positive or negative. Definition has been described as is a "positive or negative experience that is associated with a particular pattern of physiological activity." According to other theories, emotions are not causal forces but simply syndromes of components, which might include motivation, feeling, behavior, and physiological changes, but no one of these components is the emotion. Nor is the emotion an entity that causes these components

What system of the body is related to emotion's physiology?