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Grey rami communicantes to spinal nerves

Postganglionic · All 31 spinal nerves α1 vessels ACh → M3 sweat

Unmyelinated postganglionic axons leave every chain ganglion through a grey ramus to join all 31 pairs of spinal nerves and travel in the peripheral nerves to the skin and limb vessels. Supply to the limbs and body wall therefore follows peripheral nerve territory, not dermatomes alone.

Traced from the start

  1. Sympathetic (thoracolumbar) outflow
  2. Intermediolateral cell column T1–L2 via white rami communicantes
  3. Paravertebral sympathetic chain ganglia (including stellate)
  4. Grey rami communicantes to spinal nerves

Detail

Fibre types
Sudomotor (cholinergic, M3), vasoconstrictor (α1), pilomotor (α1) — all in the same peripheral nerve as the somatic fibres
Limb supply levels
Upper limb T2–T6 via stellate and middle cervical ganglia; lower limb T10–L2 via lumbar and sacral ganglia
Ratio
Grey rami outnumber white rami — every spinal nerve receives a grey ramus, only T1–L2 give a white ramus

When it goes wrong

Complete division of a peripheral nerve (e.g. ulnar at the wrist)

The territory is dry, warm and does not sweat because sudomotor and vasomotor fibres were cut with it; preserved sweating suggests an incomplete or non-organic lesion

Sympathetically maintained pain after a limb fracture or surgery

Complex regional pain syndrome: burning allodynia with colour and temperature change, swelling and abnormal sweating in a non-dermatomal distribution

Practise this structure

2 questions in the bank tagged Peripheral Nerve Injury.

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