Sympathetic vs. Parasympathetic Nervous System: Understanding the "Fight or Flight" and "Rest and Digest" Responses
This question popped up in the 2013/14 exams:
Q. Compare and contrast the sympathetic nervous system (CNS) and parasympathetic nervous system [Q. 4 (2013/14)]
Let’s break it down. Both the sympathetic and parasympathetic nervous systems are part of the autonomic nervous system (ANS). This system is like the autopilot of your body, regulating crucial functions like breathing, heart rate, and digestion without you even thinking about it. It’s also sometimes called the vegetative or involuntary nervous system.
Think of the ANS as having two complementary branches:
- Sympathetic Nervous System: This is your body’s "fight or flight" system, kicking in during times of stress or danger.
- Parasympathetic Nervous System: This is your "rest and digest" system, promoting relaxation and recovery.
Here’s a table summarizing the key differences:
| Feature | Sympathetic Nervous System | Parasympathetic Nervous System |
|---|---|---|
| Definition | One of the main parts of the ANS that controls the body’s "fight or flight" responses | A division of the ANS that controls the "rest and digest" functions of the body |
| Function | Prepares the body for emerging situations | Maintains conserving functions when the body is at rest |
| Nerves | Adrenergic and cholinergic | Cholinergic |
| Ganglia | Occur on either side of the spinal cord as 2 lateral chains | Occur individually in the organs and tissues |
| Preganglionic fibres | Short | Long |
| Postganglionic fibres | Long | Short |
| Fibre types | Usually myelinated B-fibres | Usually unmyelinated C-fibres |
| Location of preganglionic fibres | Thoracolumbar segments of the spinal cord | Nuclei of cranial nerves III, VII, IX & X and S3, S3 & S4 spinal segments |
In a nutshell:
The sympathetic and parasympathetic nervous systems work in a delicate balance to maintain your body’s internal equilibrium. Understanding their distinct roles is key to grasping how your body responds to its environment.
Sympathetic vs Parasympathetic Nervous System: Key Differences
The sympathetic and parasympathetic nervous systems are two branches of the autonomic nervous system. While both originate from the spinal cord and significantly influence physiological processes like respiration, circulation, digestion, urination, and reproduction, they differ in their structure and function.
Here’s a table highlighting the key differences:
| Feature | Sympathetic Nervous System | Parasympathetic Nervous System |
|---|---|---|
| Origin | Thoracic and lumbar segments of the spinal cord | Cranial nerves III, VII, IX & X and S3, S3 & S4 spinal segments |
| Location of ganglia | Close to the spinal cord | Away from the spinal cord, near or in the target organ |
| Location of postganglionic fibres | Near or in the target organ | Away from target organ |
| Overall effect | Excitatory ( "fight or flight" response) | Inhibitory ("rest and digest" response) |
Both systems have preganglionic and postganglionic neurons.
