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Overview of the Sympathetic and Parasympathetic Nervous System

• The autonomic nervous system (ANS) has two major divisions: sympathetic and parasympathetic.

Sympathetic Nervous System

• Pathways from the CNS:

  • Communicates with the sympathetic chain ganglia alongside the vertebral column.

  • Myelinated fibers (white fibers) versus unmyelinated fibers (gray fibers).

Options in Sympathetic Innervation

1. **Pathway to Body Wall:

• Origin:** Lateral horn of the spinal cord.

• Travels through white ramus to sympathetic chain, synapses, and returns via gray ramus to the spinal nerve.

• Innervates body wall structures (muscles, skin, bones).

2. Pathway to Thoracic Viscera:

• Origin: Similar to first option but only from T1 to T4 spinal levels.

• Innervates: Heart and lungs directly, bypassing the gray ramus.

3. Pathway to Abdominal Viscera:

• Origin: Spinal levels T5 to L2.

• No synapse in the sympathetic chain.

• Fibers converge to form splanchnic nerves: greater, lesser, and least splanchnic nerves.

• These nerves synapse in the abdominal ganglia (preaortic, prevertebral, or collateral).

Abdominal Ganglia

• Function: Postganglionic fibers innervate abdominal and pelvic viscera.

• Named for their anatomical location relative to the aorta:

  • Celiac ganglion (associated with celiac trunk)

  • Superior mesenteric ganglion (associated with superior mesenteric artery)

  • Inferior mesenteric ganglion (associated with inferior mesenteric artery)

Adrenal Gland and Neuroendocrine Function

• Adrenal medulla functions as a sympathetic ganglia.

• Splanchnic nerve fibers synapse on neuroendocrine cells, releasing catecholamines (epinephrine and norepinephrine) into the bloodstream.

Parasympathetic Nervous System

• Also comprised of two neurons with a ganglion, similar to the sympathetic system.

• Origin: Cranial nerves (III, VII, IX, and X) and sacral spinal segments (S2 to S4).

  • **Cranial Portion Profiles:

  • III:** Oculomotor (innervates eye).

  • VII:** Facial (innervates salivary and lacrimal glands).

  • IX:** Glossopharyngeal (innervates parotid salivary gland).

  • X:** Vagus nerve (innervates thoracic and abdominal viscera).

Intrinsic Ganglia

• Parasympathetic ganglia are located in the walls of target organs (intrinsic ganglia).

• Preganglionic fibers are myelinated and synapse directly within the walls of the organs they innervate.

Functions of the Parasympathetic System

• Promotes rest and digest functions.

• Provides innervation for pelvic organs via pelvic splanchnic nerves (S2-S4).

  • Targets: Descending colon, sigmoid colon, urinary bladder, and reproductive organs.

  • Functions support processes like sexual arousal and enhancing digestion.

Summary

• Sympathetic Division: Involves pathways originating from T1 to L2, with diverse roles in managing body responses including stress (fight or flight).

• Parasympathetic Division: Originates largely from cranial nerves and sacral segments, facilitating non-emergency bodily functions crucial for comfort and recovery.