Sympathetic vs. Parasympathetic: What's the Difference?
Read the comparison below, or explore it visually. Create a visual lesson comparing sympathetic and parasympathetic using available credits or plan allowance.
The sympathetic nervous system prepares the body for action, the fight-or-flight response, while the parasympathetic nervous system calms it and supports rest and digestion. Both are divisions of the autonomic nervous system, which runs organs without conscious control. Most organs receive nerves from both, and the balance between them sets heart rate, pupil size, digestion and many other functions moment to moment.
At a glance
| Sympathetic | Parasympathetic | |
|---|---|---|
| Main role | Fight or flight: mobilises energy | Rest and digest: conserves energy |
| Heart and lungs | Faster heartbeat, wider airways | Slower heartbeat, narrower airways |
| Digestion and eyes | Slows digestion, dilates pupils | Boosts saliva and digestion, constricts pupils |
| Where nerves exit | Thoracic and upper lumbar spinal cord | Brainstem (e.g. vagus nerve) and sacral cord |
| Main signal at organs | Mostly noradrenaline (norepinephrine) | Acetylcholine |
Which should you use?
The sympathetic system takes over in sudden stress or exertion, such as swerving to avoid a scooter on a busy road, when the heart races, pupils widen and adrenaline is released.
The parasympathetic system dominates during calm, such as resting after a meal, when the heart slows, saliva and digestive juices flow and the intestines move food along.