Understanding the Autonomic Nervous System: Sympathetic vs. Parasympathetic
The autonomic nervous system (ANS), also known as the vegetative or involuntary nervous system, is responsible for maintaining the homeostasis of our vital functions. This system is always working behind the scenes, ensuring our bodies remain balanced and functioning without our conscious effort. The ANS is further divided into two branches: the sympathetic and parasympathetic nervous systems. While they work together, each system has a distinct role in regulating our bodily functions.
Let’s break down the key differences between the sympathetic and parasympathetic nervous systems:
| 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 two 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 … |
(This is part 1 of a 2-part blog post. Stay tuned for part 2 where we further explore the functions and differences between the sympathetic and parasympathetic nervous systems.)
| Feature | Sympathetic Nervous System | Parasympathetic Nervous System |
|---|---|---|
| Type of nerve fibres | Mostly myelinated preganglionic fibres | Usually unmyelinated Cfibres |
| Location of preganglionic fibres | Thoracolumbar segments of | Nuclei of cranial nerves III, |
| the spinal cord | VII, IX & X and S3, S3 & S4 spinal segments | |
| Location of postganglionic fibres | Away from target organ | Near or in the target organ |
| Overall effect | Excitatory | Inhibitory |
Both are part of the autonomic nervous system. Both originate from the spinal cord. Both have huge influence on physiological processes such as respiration, circulation, digestion, urination and reproduction. Both have preganglionic and postganglionic neurons.
