Actions of the sympathetic and parasympathetic nervous systems
1. Compare and contrast the actions of the sympathetic and parasympathetic nervous systems
. Include information about pre & postganglionic fiber length, origin of fibers, location of ganglia, effect on heart rate & blood pressure, effect on digestion, & effect on respiration.
Sample Solution
Sympathetic vs. Parasympathetic Nervous System: A Balancing Act
The autonomic nervous system regulates our body's unconscious functions, maintaining homeostasis (internal stability). Within this system, the sympathetic and parasympathetic nervous systems work in opposition to create a dynamic equilibrium. Let's delve into their contrasting actions:
| Feature | Sympathetic Nervous System (Fight-or-Flight) | Parasympathetic Nervous System (Rest-and-Digest) |
|---|---|---|
| Origin of Fibers | Thoracolumbar spinal cord (T1-L2) | Brainstem (cranial nerves III, VII, IX, X) and sacral spinal cord (S2-S4) |
| Ganglia Location | Near the spinal cord (paravertebral ganglia) or close to target organs (peripheral ganglia) | Close to or within target organs |
| Pre- vs. Postganglionic Fibers | Short preganglionic fibers, long postganglionic fibers | Long preganglionic fibers, short postganglionic fibers |
| Effect on Heart Rate | Increases heart rate (positive chronotropic effect) | Decreases heart rate (negative chronotropic effect) |
| Effect on Blood Pressure | Increases blood pressure (vasoconstriction) | Decreases blood pressure (vasodilation) |
| Effect on Digestion | Reduces digestion (inhibits GI motility) | Increases digestion (stimulates GI motility) |
| Effect on Respiration | Increases respiration rate and depth | May decrease respiration rate and depth |
Full Answer Section
Explanation:
- Fiber Length:Â The sympathetic system has a shorter preganglionic fiber and a longer postganglionic fiber. This allows for widespread activation of organs throughout the body from a centralized location in the spinal cord. Conversely, the parasympathetic system has a longer preganglionic fiber and a shorter postganglionic fiber. This is because its ganglia are often located closer to or within the target organs, allowing for more focused control.
- Heart Rate & Blood Pressure:Â During a stressful situation, the sympathetic system kicks in, increasing heart rate and blood pressure to prepare the body for action. The parasympathetic system, on the other hand, promotes relaxation by slowing heart rate and lowering blood pressure.
- Digestion & Respiration:Â When the body is focused on immediate needs like escaping danger, digestion takes a backseat. The sympathetic system reduces digestive activity. The parasympathetic system, however, promotes digestion and a return to a normal state by increasing GI motility. Both systems influence respiration, although the sympathetic system generally increases the rate and depth of breathing during exertion, while the parasympathetic system allows for a more relaxed breathing pattern.
Maintaining Balance:
The sympathetic and parasympathetic nervous systems work together to maintain a healthy equilibrium within the body. This allows us to respond effectively to both internal and external stimuli, shifting between states of alertness and relaxation as needed.