Autonomic nervous system
The autonomic nervous system (ANS) controls many of the body’s involuntary functions, such as heart rate, digestion, and breathing. It is primarily controlled by nerves from the spinal cord, specifically between T1 and L2.
Key functions of the autonomic nervous system
- Heart muscles: Regulates heart rate, rhythm and cardiac output.
- Blood vessels: Manages the ability to dilate and constrict blood vessels.
- Glands: Stimulates glands like the adrenal glands to release hormones, such as adrenaline.
- Smooth muscles: Controls muscles in organs like the intestines and bladder.
- Organs: Oversees the functions of internal organs (also called viscera).
Components of the autonomic nervous system
1. Sympathetic nervous system (SNS):
Activated during the “fight or flight” response, it prepares the body for action. The ‘fight’ response includes:
- The ‘fight‘ response includes:
- increased heart rate
- release of adrenaline
- constriction of blood vessels to direct blood to areas where it is needed most.
- The “flight” part of the response
- slows down certain functions, such as digestion and urinary control.
2. Parasympathetic Nervous System (PNS):
Often referred to as the “rest and digest” system, it slows down body functions after stress and promotes rest, digestion, and energy conservation.
3. Enteric Nervous System (ENS):
Sometimes called the “second brain,” it controls the functions of the gastrointestinal system.
How spinal cord injury affects the autonomic nervous system
A spinal cord injury can disrupt the connection between the brain and autonomic pathways, leading to an imbalance in the autonomic nervous system. This often results in reduced sympathetic activity and an overactive parasympathetic system.
The sympathetic nervous system originates in the thoracolumbar spinal cord (T1–L2). Spinal cord injuries at or above T6, can severely disrupt the sympathetic nervous system, impairing its function.
Effects of autonomic nervous system disruption after spinal cord injury
Cardiac issues: Including arrhythmias (irregular heartbeats).
Low blood pressure: Known as systemic hypotension.
Respiratory problems: Such as bronchoconstriction (narrowing of the airways) and increased secretions in the lungs.
Bowel and bladder control: Loss of voluntary control over these functions.
Exaggerated reflexes: Uncontrolled responses to stimuli.
Sexual dysfunction: Problems with sexual health and function.
Temperature regulation issues: Difficulty maintaining normal body temperature.
Read more about how the autonomic nervous system modulates other body systems via the links below:
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Henke, A., Billington, Z., & Gater, D. (2022). Autonomic dysfunction and management after spinal cord injury: A narrative review. Journal of Personalized Medicine, 12(7), 1110. https://doi.org/10.3390/jpm12071110
Krassioukov, A., Stillman, M., & Beck, L. A. (2020). A primary care provider’s guide to autonomic dysfunction following spinal cord injury. Topics in Spinal Cord Injury Rehabilitation, 26(2), 123–127. https://doi.org/10.46292/sci2602-123
Wulf, M. J., & Tom, V. J. (2023). Consequences of spinal cord injury on the sympathetic nervous system. Frontiers in Cellular Neuroscience, 17, 999253. https://doi.org/10.3389/fncel.2023.999253