Parasympathetic (Rest & Digest) vs Sympathetic (Fight & Flight) Nervous System

Difference between Sympathetic And Parasympathetic Nervous System

The sympathetic nervous system prepares the body for the “fight or flight” response during any potential danger. On the other hand, the parasympathetic nervous system inhibits the body from overworking and restores the body to a calm and composed state. The difference between the sympathetic and parasympathetic nervous system are differentiated, based on the way the body responds to environmental stimuli.

The major differences between sympathetic and parasympathetic nervous system are summarized below:

Sympathetic Division

• Involved in the fight, flight, freeze response.

• The sympathetic system prepares the body for any potential danger.

• Sympathetic system has shorter neuron pathways, hence a faster response time.

• Increases heartbeat, muscles tense up.

• The pupil dilates to let in more light.

• Saliva secretion is inhibited.

• On “fight, flight, freeze” situations, Adrenaline is released by the adrenal glands; more glycogen is converted to glucose.

Parasympathetic Division

• Involved in maintaining homeostasis and also, permits the rest and digest response.

• The parasympathetic system aims to bring the body to a state of calm.

• Has comparatively longer neuron pathways, hence a slower response time.

• Reduces heartbeat, muscles relaxes.

• The pupil contracts.

• Saliva secretion increases, digestion increases.

Hormones associated sympathetic and parasympathetic state

The sympathetic nervous system (SNS) releases the hormones (catecholamines - epinephrine and norepinephrine) to accelerate the heart rate.

The parasympathetic nervous system (PNS) releases the hormone acetylcholine to slow the heart rate.