Sympathetic stimulation has a widespread effect on the whole body, either via activation of adrenergic nerves, or in response to adrenaline and noradrenaline released from the adrenal gland ('fight and flight' response).

Sympathetic stimulation enables the body to respond to physical or emotional stress. It causes CNS arousal, a rise in blood pressure and tachycardia. Blood is directed centrally, away from non-essential organs such as the gut and skin, and energy substrates are mobilized.

The SNS controls blood pressure and thermoregulation and sympathetic responses to illness such as tachycardia, sweating and fever.