The sympathetic nervous system (or SNS) is generally associated with what is known as the fight-or-flight stress response. It is responsible for a number of other regulatory functions within the body as well. The SNS is part of a larger organization of nerves known as the autonomic nervous system (ANS). However, the sympathetic nervous system is set apart as the system that operates without conscious thought.

The sympathetic nervous system secretes acetylcholine, which activates the release of adrenaline and noradrenaline, primarily influencing the cardiovascular system. Still, the SNS regulates a number of homeostatic mechanisms in the body. Unconscious bodily functions from pupil diameter to urinary control are maintained by this complex and efficient network of nerve cells.

The SNS prepares the body for action. Nerves originating in the middle of the vertebral column spread out via axons, slender nerve projections that transmit information back and forth. From here, messages are sent to all the body’s systems.

The sympathetic nervous system is able to trigger simultaneous bodily reactions within a fraction of a second. When the fight-or-flight response kicks in, the SNS will speed up your heart, give you goose bumps, increase air flow to the lungs and blood flow to your limbs—all getting you ready to either fight or run away as fast as you can.

The SNS doesn’t just work in times of high stress. It’s up before we even hear the alarm, preparing the body for the waking state. Just as you are leaving your dreams, the SNS is restarting digestive processes, increasing blood flow and giving you a surge of energy to stretch and get out of bed.

The sympathetic nervous system takes care of the details of bodily function so we don’t have to think about it.