Why do all 31 pairs of spinal nerves receive a grey ramus communicans, whereas white rami communicantes are attached only to the T1 to L2 spinal nerves?
- A Every spinal nerve needs postganglionic sympathetic fibres for its peripheral distribution, but preganglionic sympathetic neurons exist only in the T1 to L2 intermediolateral columns ✓
- B Grey rami carry visceral afferent fibres, which leave the cord at every segment, while white rami carry motor fibres confined to T1 to L2
- C White rami contain myelinated parasympathetic fibres restricted to the thoracolumbar outflow, while grey rami carry unmyelinated parasympathetic fibres diffusely
- D Grey rami arise from collateral (prevertebral) ganglia distributed throughout, while white rami arise only from paravertebral ganglia opposite T1 to L2
Correct answer: A. Every spinal nerve needs postganglionic sympathetic fibres for its peripheral distribution, but preganglionic sympathetic neurons exist only in the T1 to L2 intermediolateral columns
Explanation
Preganglionic sympathetic cell bodies are confined to the intermediolateral cell column of T1 to L2, so myelinated preganglionic fibres (white rami) exit only there. Once relayed in paravertebral ganglia, postganglionic unmyelinated fibres must be distributed to the body wall and limbs through every spinal nerve, hence grey rami at all levels. Grey rami carry efferent postganglionic fibres, not visceral afferents, which eliminates option B.
Reference: Moore Clinically Oriented Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.