In the situation where Andrew proposes to Heidi and her heartbeat quickens, her pupils dilate, and her breath quickens as she answers, “yes!”, the parts of the nervous system that activated these responses are parts of the sympathetic nervous system (SNS). This said system is one of the two main divisions of the autonomic nervous system, the other being the parasympathetic nervous system (PSNS). The unconscious actions like dilation of the pupils, increase of contraction of the heart rate and dilation of the bronchioles in the lungs are just few of actions made possible by the autonomic nervous system. The sympathetic nervous system on the other hand causes the fight-or-flight response of the body.
