Corpus: White ramus communicans

The ramus communicans albus is a connecting branch between the spinal nerve and the sympathetic trunk. It carries the preganglionic sympathetic nerve fibres of a segment that originate in the lateral horn of the spinal cord.

The ramus communicans albus contains myelinated and non-myelinated fibres that have visceromotor and viscerosensory functions. The myelinated fibres give the nerve branch its macroscopic white appearance, which distinguishes it from the ramus communicans griseus.

The cell bodies of the preganglionic fibres of the rami communicantes albi lie ipsilaterally in the nucleus intermediolateralis of the spinal cord, which extends from Th1 to L2. The rami communicantes albi also contain visceroafferent fibres whose cell bodies are located in the dorsal root ganglia.

Once the preganglionic fibres have reached the border cord, they are either connected at segment level or they continue to ascend or descend in the border cord to form their synapse in another segment. After the connection, they run with the ramus communicans griseus to the respective spinal nerve, which leads them to the successful organs.

The preganglionic sympathetic fibres for the abdominal and pelvic organs run unconnected through the border ganglia and form the nervi splanchnici in the abdominal cavity. They only become interconnected in the prevertebral ganglia.

Although the border cord ends further caudally, there are no longer any rami communicantes albi below L2, as the nucleus intermediolateralis ends here. The fibres of the border cord below L2 originate from the rami communicantes albi from the segments Th1 to L2. Above and below Th1 to L2 there are therefore only rami communicantes grisei.

• Richard L. Drake, Wayne Vogl, Adam W. M. Mitchell: Gray's Anatomy for Students (2007), p. 82