Autonomic Nervous System (ANS)
The autonomic nervous system controls involuntary functions of internal organs, blood vessels, glands, smooth muscle, and cardiac muscle. It maintains homeostasis.
Divisions of the ANS
- Sympathetic nervous system ("Fight or Flight")
- Parasympathetic nervous system ("Rest and Digest")
Anatomy
1.Sympathetic Division
Origin: Thoracolumbar spinal cord (T1–L2)
Ganglia: Paravertebral sympathetic chain. Prevertebral ganglia
Main Effects
- Pupil dilation (mydriasis)
- Increased heart rate and blood pressure
- Bronchodilation
- Decreased gastrointestinal motility
- Increased sweating
2.Parasympathetic Division
Origin
Craniosacral outflow: CN III, CN VII, CN IX, CN X, S2–S4 spinal segments
Main Effects
- Pupil constriction (miosis)
- Decreased heart rate
- Increased gastrointestinal motility and secretion
- Bladder emptying
Physiology
The ANS regulates:
- Cardiovascular System: Heart rate. Blood pressure. Vascular tone
- Respiratory System: Bronchial tone
- Gastrointestinal System: Motility. Secretions
- Genitourinary System: Micturition. Sexual function
- Thermoregulation: Sweating. Skin blood flow
- Eye: Pupil size. Accommodation
Clinical Examination of the ANS
1. Inspection
- Observe: Skin color. Sweating. Trophic skin changes. Peripheral temperature
2. Pupillary Examination
- Evaluate: Size. Symmetry. Light reflexes
- Autonomic lesions may cause: Miosis. Mydriasis. Anisocoria
3. Cardiovascular Tests
- Orthostatic (Postural) Test
- Measure BP and pulse: Supine position. Standing position
- Orthostatic Hypotension: Fall in systolic BP ≥20 mmHg or diastolic BP ≥10 mmHg after standing
- Suggests autonomic dysfunction.
4. Sweating Assessment
- Abnormalities: Hyperhidrosis (excess sweating). Anhidrosis (absence of sweating)
5. Bladder Function
- Assess: Urinary retention. Urgency. Incontinence
6. Sexual Function
- Assess: Erectile dysfunction.Ejaculatory disorders