Sympathetic Nervous System
A division of the autonomic nervous system that mobilizes the body's resources for action, commonly known as the "fight-or-flight" response.
The sympathetic nervous system (SNS) represents one of the two main branches of the autonomic-nervous-system, serving as the body's primary mechanism for responding to stress and perceived threats. This sophisticated network of nerves plays a crucial role in maintaining homeostasis while preparing the organism for rapid response to environmental challenges.
Anatomical Structure
The SNS originates in the thoracolumbar region of the spinal cord, with nerve fibers extending through:
- Sympathetic chain ganglia
- Prevertebral ganglia
- Direct innervation to target organs
These pathways utilize two primary neurotransmitters:
- norepinephrine (primary messenger)
- acetylcholine (at some pre-ganglionic junctions)
Physiological Effects
When activated, the sympathetic nervous system triggers a cascade of responses:
Cardiovascular
- Increased heart-rate
- Enhanced blood-pressure
- Vasodilation in skeletal muscles
- Vasoconstriction in non-essential organs
Respiratory
- Bronchodilation
- Increased respiratory rate
- Enhanced oxygen uptake
Metabolic
- glucose mobilization
- Enhanced lipolysis
- Increased metabolic-rate
Other Effects
- Pupil dilation
- Reduced digestive activity
- sweat-gland activation
- Decreased salivation
Clinical Significance
The SNS plays a vital role in various clinical conditions:
- stress-response
- anxiety-disorders
- hypertension
- pheochromocytoma (rare tumor of adrenal glands)
Regulation and Balance
The sympathetic nervous system works in dynamic opposition with the parasympathetic-nervous-system, creating a balanced regulatory system. This interaction is crucial for:
- Daily physiological adaptation
- Stress response
- Recovery and rest
- circadian-rhythm maintenance
Modern Relevance
Understanding SNS function has important implications for:
The sympathetic nervous system represents a fundamental aspect of human physiology, bridging our evolutionary past with modern challenges in stress management and health maintenance.