Sympathetic nervous system

The sympathetic nervous system (SNS) is a branch of the nervous system which acts to prepare the body for fight or flight in times of stress by controlling the function of organs throughout the body. SNS activation is therefore often referred to as the “fight or flight response”. This activation triggers increased levels of adrenaline and noradrenaline which results in an increase in heart rate, blood pressure, blood sugar, sweating, pupil dilation and air passage dilation and decreases the function of processes unnecessary for survival such as digestion. This stress response differs from the HPA axis as it is activated immediately, providing a more rapid but short-lived response. Pocock, G., Richards, C. and Richards, D. (2006). Human Physiology. 4th ed. China: Oxford University Press, p.178. Ulrich-Lai, Y.M. and Herman, J.P., 2009. Neural regulation of endocrine and autonomic stress responses. Nature reviews neuroscience, 10(6), p.397.