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StatPearls . Endowment Island (FL): StatPearls Publishing; 2021 Jan-.



The white ramus communicans (pl. White rami communicantes), which is likewise known together the white interacting branch or the white connecting ramus, consists of preganglionic fibers of the sympathetic system. The white ramus communicans is a structure that anteriorly connect the spinal nerve come the forgiveness trunk. Every preganglionic forgiveness neurons traverse v a white ramus communicans. Though sympathetic neurons arise from the spinal cord with the ventral source to get in a white ramus, their process after that can vary in four various ways. Forgiveness neurons monitor the pattern of passing through the white ramus together preganglionic neurons, synapsing top top a ganglion, and also then innervating their particular organs as postganglionic neurons. Ultimately, these sympathetic fibers target blood vessels, sweat glands, arrector chili muscles, and visceral organs come elicit a "fight or flight" physiological response.

Structure and also Function

White rami communicantes affix preganglionic forgiveness neurons of the spinal cord to the sorry trunk. The forgiveness trunk consists of a sorry ganglion because that each corresponding vertebral level. White rami communicantes bring organization come the forgiveness outflow of nerves. Back white rami communicantes save both myelinated and also unmyelinated axons, they contain a higher density that myelinated axons. Hence, the term “white” in the name. White rami room lateral to the gray rami, their post-ganglionic unmyelinated sorry counterpart. 

White rami communicantes duty ipsilaterally and appear ~ above both political parties of the spinal column. As component of the sorry system, white rami communicantes originate from the thoracolumbar (T1 come L2) vertebral outflows. Over the T1 and below the L2 vertebral outflows, white rami space absent; just gray rami exist in these regions. In the thoracic part (T1 come T12), the thoracic nerve divides into the anterior and ventral rami that the thoracic nerve. White rami communicantes originate from the anterior rami the the thoracic nerve, which are additionally called the intercostal nerves. In the lumbar regions where white rami are discovered (L1 come L2), the white rami communicantes originate straight from the lumbar nerves.

Nerves of white rami have distinct courses. Neurons that traverse with the white rami originate native the intermediolateral cell column (lateral horn of the spinal cord). The intermediolateral cell column spans indigenous T1-L2.<1> From the intermediolateral cabinet column, sympathetic neurons departure the spinal cord v the ventral root and also merge at the spinal nerve with various other neurons. Just sympathetic neurons then go into a white ramus communicans, which branches anteriorly native the spinal nerve top top the sympathetic trunk. The white rami communicantes administer a course for preganglionic sympathetic neurons that the spinal nerve to go into the sympathetic trunk. Native here, neurons deserve to take one of 4 courses: 

Ascend or descend the sympathetic trunk. There is no synapsing onto its corresponding sympathetic ganglion, axons have the right to ascend or descend the forgiveness trunk before synapsing right into a ganglion that a various level. Postganglionic forgiveness nerves can then take trip to the spinal nerve via gray ramus communicans.
Enter the cardiopulmonary splanchnic nerve. In T2 to T4 vertebral levels, neurons that the white rami communicantes synapse at their matching sympathetic ganglion and enter the thoracic, cardiac branches. This postganglionic neurons ultimately innervate the heart, lungs, and also trachea.
Enter the abdominopelvic splanchnic nerve. In T5 come L2, some sympathetic neurons can course with the white rami communicantes and also sympathetic trunk without synapsing. In T5 come T12, neurons travel with a splanchnic nerve (the greater, the lesser, or the least thoracic splanchnic nerve) and synapse in ~ a peripheral ganglion. In L1 come L2, neurons travel with the lumbar splanchnic nerve prior to synapsing in ~ a peripheral ganglion. The postganglionic sympathetic neurons deserve to then proceed to innervate visceral organs, such together the stomach, liver, intestines, kidney, adrenal glands, pancreas, bladder, gonads, and genitals.

Postganglionic entrance into a spinal nerve frequently involves the gray rami communicantes. Forgiveness innervation to the heart and other visceral organs entails splanchnic nerves that straight emerge indigenous the forgiveness ganglion.

The sympathetic preganglionic neurons sustained by the white rami communicantes ultimately target blood vessels, sweat glands, and arrector chili muscles. The sorry nerves of the splanchnic routes result in the autonomic control of the heart and also visceral organs. The white rami communicantes administer a structure that separates and also guides preganglionic sorry neurons into the sorry trunk and also its ganglia.<2><3><4>


White rami communicantes have from stems neural stakes cells. These neural comb cells migrate ventrally indigenous the dorsal portion of the neural tube and give climb to neuroblasts. Few of the forgiveness neuroblasts synapse with fibers the the spinal cord to form the white rami communicantes and also other sections of the sympathetic nervous system.<5>

Blood Supply and Lymphatics

The white rami communicantes are usually close come the intercostal lymph nodes and also intercostal lymph vessels.


In enhancement to hold preganglionic sympathetic outflows that the spinal cord, such as efferent outflows, the T5 come T9 white rami communicantes can additionally contain general afferent (sensory) visceral inflows. These basic afferent visceral fibers classify as neither sympathetic nor parasympathetic; however, visceral afferent fibers often tend to associate anatomically through sympathetic efferent fibers. Together a result, signals from sensory receptors of visceral organs also travel v the peripheral ganglion, sympathetic trunk, and also the white rami communicantes. After traveling v the white rami communicantes and the spinal nerve, this visceral afferent fibers then get in the spinal cord via the dorsal source of the spinal cord. Afferent visceral nerves frequently synapse onto the preganglionic sorry neurons situated in the intermediolateral cabinet column.<6>


White rami communicantes host fibers that at some point innervate cardiac tissue, arrector chili muscles, and smooth muscle that visceral organs and also vasculature. 

Physiologic Variants

Physiological variations, especially those situated in the top thoracic areas (T2 to T5), are numerous for white rami communicantes:

In the T1 level, the white rami communicantes that the spinal nerve can show up medial come its equivalent gray rami communicantes. Normally, white rami are lateral come gray rami.
The horizontal distance from the sorry trunk to the distal allude of a white ramus communicans can selection from 2.5 come 28.5 millimeters.
Sometimes T5 can additionally send postganglionic sympathetic neurons into the cardiothoracic nerve branches.
In T2, T3, and T4 levels, the is feasible for extr gray or white rami to prolong to a various level ganglion that the sorry trunk. T2 experiences the most far-reaching presence that ascending and also descending rami.
It is possible, in fact, quite regular (85.7%), to watch bilateral asymmetry as soon as comparing white and also gray rami.
When considering both gray and also white rami communicantes, one of each communicating rami are expected to enter each ganglion. However, it is possible for a sorry ganglion in T2, T3, and T4 ganglion levels to have all over from 1 to 4 communicating rami.

Surgical Considerations

Sympathectomy and also ramicotomy, the procedures of disrupting the forgiveness trunk and also the connecting branches, can be conducted to attenuate the effects of problems such as hyperhidrosis. Compared to sympathectomy, which has been thought about the “gold standard” because that the treatment of idiopathic hyperhidrosis, the procedure the ramicotomy calls for a much longer operation time. It can result in more comprehensive variability in the severity that compensatory sweating.<8>

Clinical Significance

Sympathectomy is the most common surgical treatment used to settle severe hyperhidrosis. Hyperhidrosis is a problem that results in extreme sweating in certain areas of the body, such as the face, hands, and also armpits. Number of studies have actually explored the impacts of ramicotomy in dealing with hyperhidrosis. One of the main side effects of both sympathectomy and ramicotomy involves compensatory hyperhidrosis, i m sorry is the compensatory sweat in other large areas of the body. Compensatory sweat is frequently the chef post-operative patient complaints.

Severe axillary hyperhidrosis, palmar hyperhidrosis, and craniofacial hyperhidrosis have received treatment with ramicotomy. In all species of hyperhidrosis, selective ramicotomy of the top thoracic region has displayed an advancement in the top quality of life and reduced focal length sweating. Part instances confirmed that ramicotomy regularly resulted in a lowered rate of compensatory sweating, when other instances displayed an boosted rate of compensatory sweating. Post-operative compensatory hyperhidrosis early to ramicotomy because that the therapy of severe hyperhidrosis can display a wide variety of severity.

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A transverse slice v the thoracic an ar is displayed in the picture. The rami communicantes space labeled and drawn as 2 nerves that anteriorly leg the spinal nerve top top a ganglion the the sympathetic trunk. The white ramus communicans is the lateral (more...)


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