The two divisions of the autonomic nervous system, the sympathetic and parasympathetic nervous systems, work antagonistically to maintain homeostasis: the sympathetic system activates "fight or flight" responses, while the parasympathetic system promotes "rest and digest" functions.
Sympathetic Nervous System: "Fight or Flight"
The sympathetic nervous system prepares the body for action in stressful or emergency situations. Its primary functions include:
- Increased Heart Rate and Blood Pressure: To deliver oxygen and nutrients more efficiently to muscles.
- Dilation of Pupils: To improve vision.
- Release of Glucose: From the liver to provide energy.
- Dilation of Bronchioles: In the lungs to increase oxygen intake.
- Suppression of Non-Essential Functions: Such as digestion and urination, to conserve energy.
Essentially, the sympathetic nervous system gears the body up for immediate action, allowing it to cope with perceived threats or challenges.
Parasympathetic Nervous System: "Rest and Digest"
The parasympathetic nervous system conserves energy and maintains bodily functions at a baseline level. Its primary functions include:
- Slowing Heart Rate and Lowering Blood Pressure: To conserve energy.
- Constriction of Pupils: To adjust to normal light levels.
- Stimulation of Digestion: To process food and absorb nutrients.
- Stimulation of Salivation and Gastric Secretions: To aid in digestion.
- Promoting Urination and Defecation: To eliminate waste.
In essence, the parasympathetic nervous system facilitates relaxation, recovery, and essential bodily processes.
| Feature | Sympathetic Nervous System | Parasympathetic Nervous System |
|---|---|---|
| Primary Function | "Fight or Flight" - Arousal and Action | "Rest and Digest" - Relaxation and Repair |
| Heart Rate | Increases | Decreases |
| Blood Pressure | Increases | Decreases |
| Digestion | Inhibits | Stimulates |
| Pupils | Dilates | Constricts |
| Bronchioles | Dilates | Constricts |
The interplay between the sympathetic and parasympathetic systems ensures that the body can adapt to a wide range of situations, maintaining a stable internal environment. They create a balancing act, where the sympathetic nervous system activates body processes, and the parasympathetic deactivates or lowers them.
