Thoracolumbar Outflow [Neurosurgery Wiki]

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===== Thoracolumbar Outflow =====

The **thoracolumbar outflow** refers to the anatomical origin of the **sympathetic division** of the **autonomic nervous system**, which arises from the **thoracic and lumbar segments** of the spinal cord.

==== Definition ====
The **thoracolumbar outflow** comprises the **preganglionic sympathetic neurons** located in the **intermediolateral cell column (IML)** of the **spinal cord segments T1 to L2/L3**.

==== Pathway ====
  * Preganglionic neurons originate in the **IML** (lateral horn)
  * Their axons exit the spinal cord through **ventral roots**
  * They pass through **white rami communicantes** to reach:
    * **Paravertebral ganglia** (sympathetic chain)
    * Or **prevertebral ganglia** (e.g., celiac, superior mesenteric)
  * Postganglionic fibers then project to:
    * Viscera (heart, lungs, GI tract)
    * Blood vessels
    * Sweat glands
    * Pupillary dilator muscles

==== Functional Roles ====
  * ↑ Heart rate and cardiac output
  * ↑ Pupil dilation (mydriasis)
  * Bronchodilation
  * ↓ Gastrointestinal motility
  * Vasoconstriction in skin and viscera
  * Sweat secretion

==== Comparison ====
^ Division ^ Origin ^ Key Features ^
| Sympathetic (Thoracolumbar) | T1–L2/L3 | "Fight or flight" responses |
| Parasympathetic (Craniosacral) | Cranial nerves III, VII, IX, X + S2–S4 | "Rest and digest" responses |

==== Clinical Relevance ====
  * Lesions affecting T1–L2 segments can impair sympathetic function
  * Disruption may cause:
    * Orthostatic hypotension
    * Thermoregulatory dysfunction
    * Bladder/bowel dysfunction

==== Related Entries ====
  * [[autonomic_nervous_system:sympathetic_nervous_system]]
  * [[neuroanatomy:intermediolateral_cell_column]]
  * [[physiology:fight_or_flight_response]]