Answer
A visceral motor neuron originates in the lateral horn of the grey matter of the spinal cord, It passes through the ventral root and then through the ventral ramus of the spinal nerve. Next it passes through the white ramus communicantes of the sympathetic trunk (myelinated fibers). It then synapses with a postsynaptic neuron in a ganglion of the sympathetic trunk. The post synaptic ganglion then leaves for the periphery via a gray ramus communicantes and then through the ventral ramus of the spinal nerve.
The white rami communicantes carry presynaptic myelinated fibers. The gray rami communicantes carry postsynaptic unmyelinated fibers.
Work Step by Step
The sympathetic trunk with its ganglia run beside the vertebral column. A spinal nerve is formed by a dorsal root -- which issues from the dorsal horn-- and a ventral root which issues from the ventral horn. of the spinal cord gray matter. The dorsal root has a dorsal root ganglion.
The visceral motor presynaptic neuron originates in the lateral horn of the spinal cord gray matter. It travels through the ventral root to the spinal nerve. It passes through the ventral ramus of the spinal nerve on through the white ramus communicantes to a sympathetic trunk ganglion. At this point the presynaptic neuron has three alternatives: 1. It may synapse with a post-synaptic neuron at the level of entry of the sympathetic trunk. 2. It may synapse with a postsynaptic neuron at a higher or lower level of the sympathetic trunk. 3. It may synapse with a distant collateral ganglion ( for example a celiac ganglion) anterior/ventral to the vertebral column.
White rami communicantes carry myelinated preganglionic sympathetic fibers.. They are located adjacent to cord segments T1-L2 of the sympathetic system outflow.
Gray rami carry post-ganglionic unmyelinated fibers which pass to the periphery. They issue from every sympathetic trunk ganglion from cervical to sacral region.
Rami communicantes are associated only with the sympathetic division of the autonomic nervous system and not with the parasympathetic division.
