Organization of the ANS

Organization of the autonomic nervous system (ANS) includes sympathetic and parasympathetic divisions controlling involuntary functions.

What is the Autonomic Nervous System (ANS)?

• The Autonomic Nervous System (ANS) is a part of the Peripheral Nervous System (PNS) that controls involuntary body functions—those that happen without conscious thought.
• It regulates: Heart rate, Breathing rate, Digestion, Pupillary response, Urination, sexual arousal, and more
• It ensures that the internal environment of the body remains stable, a state called homeostasis.

Organization of the ANS

The ANS is divided into three main components:

1. Sympathetic Nervous System (SNS) – “Fight or Flight”

• Origin: Thoracolumbar region (T1–L2) of the spinal cord
• Function: Prepares the body for stressful or emergency situations
• Key Effects:
  • Increases heart rate and blood pressure
  • Dilates pupils
  • Inhibits digestion
  • Dilates bronchioles (for more oxygen)
  • Mobilizes energy (glucose release)

2. Parasympathetic Nervous System (PNS) – “Rest and Digest”

• Origin: Craniosacral region (brainstem and sacral spinal cord)
• Function: Promotes relaxation and conserves energy
• Key Effects:
  • Slows heart rate
  • Stimulates digestion
  • Constricts pupils
  • Promotes urination and defecation
  • Encourages sexual arousal

3. Enteric Nervous System (ENS) – “Brain of the Gut”

• Location: Embedded in the lining of the gastrointestinal tract
• Function: Controls gastrointestinal functions independently but is influenced by both sympathetic and parasympathetic systems
• Key Effects:
  • Regulates enzyme secretion
  • Controls peristalsis (movement of food)
  • Manages blood flow in the gut

Sympathetic vs. Parasympathetic – Key Differences

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