Above T1 and below L2, the sympathetic trunk is attached to the spinal nerve actually, its ventral primary ramus only by gray rami communicantes. There are NO white rami in the neck or below L2. Unauthorized use prohibited. Through these nerve fibers the central nervous system controls the activity of all the nerve cells in the sympathetic trunk. Thus it can alter the secretion of sweat, the amount of blood flowing through the various tissues, and the erection of hairs goose-flesh throughout the body by way of the processes of the sympathetic nerve cells that are distributed through the spinal and cranial nerves.
It is important to note that the nerve fibers which connect the central nervous system to the sympathetic nervous system run only in the first thoracic to second or third lumber spinal nerves. If all these nerves or the white rami communicants arising from them were cut, the sympathetic nervous system would be separated from the control of the central nervous system.
This would result in the loss of a number of responses which arise from afferent impulses discharging directly into the central nervous system over the dorsal roots, e. On left side general arrangement of somatic system is shown. On right side general arrangement of sympathetic system is shown. Gray ramus is shown in gray color and white ramus is shown in white color. Note the postganglionic fiber entering into dorsal ramus. Do remember that gray ramus is connected to anterior or ventral ramus.
Gray rami communicantes Soon after its formation, each ventral ramus receives a slender bundle of non-myelinated nerve fibers from the corresponding ganglion of sympathetic trunk. This bundle of non-myelinated nerve fibers is given the name the gray ramus communicans. It is proximal to white ramus. They are gray colored because the nerve fibers in these rami are devoid of myelin.
They bring postganglionic sympathetic fibers to ventral rami and are distributed through their branches. They also enter every branch of dorsal ramus. Gray ramus contains non-myelinated efferent postganglionic fibers that leave the paravertebral ganglion and pass to anterior ventral or posterior dorsal ramus of spinal nerve.
These sympathetic fibers supply smooth muscles of blood vessels, smooth muscles of the hair arrector pilorum and the sweat glands. Thus the spinal nerve supplies involuntary and voluntary structures.
The fibers in gray ramus are those that are distributed via the branches of spinal nerve to blood vessels vasomotor fibers , sweat glands sudomotor fibers and arrector pili muscles pilomotor fibers. Every spinal nerve receives a gray ramus All thoracic and the upper two lumbar nerves have gray rami and white rami. All cervical, lower lumbar and all sacral nerves do not have gray rami, because there is no sympathetic outflow from these segments of spinal cord.
The ganglia with which these nerves are connected by their white rami receive their preganglionic fibers from thoracolumbar lateral horn cells whose fibers after entering sympathetic trunk have gone up or down in it. The arrangement of sympathetic fibers in cervical region Note that There is no gray ramus The preganglionic fibers do not synapse in the sympathetic ganglion and ascend upwards Superior cervical ganglion gives off four gray rami.
Middle cervical ganglion gives off two gray rami. Inferior cervical ganglion gives off two gray rami. Stellate ganglion which is formed by the fusion of inferior cervical ganglion and first thoracic ganglion, gives three gray rami and one white ramus communicans.
Note that the gray rami contain only efferent postganglionic fibers but white rami contain efferent preganglionic and afferent fibers.
The arrangement of sympathetic fibers in lower lumbar and all sacral nerves Note that There is no gray ramus The preganglionic fibers do not synapse in the sympathetic ganglion and descend downwards There are two sympathetic trunks one on each side of the vertebral column. Each trunk consists of a vertical chain of ganglia. These ganglia are united by nerve fibers. They extend the whole length of vertebral column.
Each sympathetic trunk extends alongside the vertebral column from the base of the skull to the coccyx. In neck, the trunks lie anterior to the transverse processes of cervical vertebrae.
There are three ganglia in cervical region Superior cervical Middle cervical and Inferior cervical ganglia Occasionally middle cervical ganglion is absent Inferior cervical ganglion and first thoracic ganglion often unite to form stellate ganglion. Sometimes second thoracic may also be included or even third and fourth thoracic may be In thorax, sympathetic trunks lie on the sides of vertebral bodies, anterior to the heads of ribs.
There are eleven or twelve ganglia in thoracic region. They are named according to their number; first thoracic ganglion, second thoracic ganglion, etc. In abdomen, the trunks are anterolateral to the sides of the bodies of lumbar vertebrae. There are four or five ganglia in lumbar region. They are first lumber ganglion, second lumbar ganglion and so on. In pelvis, sympathetic trunks are anterior to sacrum.
There are four or five ganglia in sacral region. They are first sacral ganglion, second sacral ganglion and so on. Superiorly the proximal ends of sympathetic trunks are separate but inferiorly the two trunks join each other at a single ganglion. This ganglion where the two trunks join is called ganglion impar. Theoretically there is a ganglion for each spinal nerve, but fusion occurs, especially in the cervical region. First four ganglia unite to form superior cervical ganglion.
Fifth and sixth ganglia join to form middle cervical ganglion. Seventh and eighth cervical ganglia fuse and form inferior cervical ganglion. Elsewhere there is usually one ganglion less than the number of nerves There are usually 11 thoracic ganglia but there may be twelve also There may be 4 lumbar ganglia but may be 5also and There are 4 sacral ganglia. Diagrammatic representation of paravertebral sympathetic ganglia. The anterior aspect of vertebral column is shown. The paravertebral ganglia are linked together and form two right and left sympathetic chains.
Splanchnic nerves The preganglionic efferent sympathetic nerve fibers enter the sympathetic ganglia via white rami communicantes Some of them synapse their Some ascend and some descend without synapsing Some pass through the ganglia without synapsing. They do not ascend or descend. These myelinated fibers leave the sympathetic trunk as greater splanchnic, lesser splanchnic and lowest or least splanchnic nerves. A part of sympathetic system showing preganglionic fibers which do not synapse in sympathetic chain ganglia and pass through these ganglia without synapsing and synapse in prevertebral ganglia with postganglionic neurons Postganglionic fibers arise here in prevertebral ganglia Greater splanchnic nerves Right and left greater splanchnic nerves are formed from the branches from fifth to ninth thoracic ganglia on both sides.
They descend obliquely on the sides of the bodies of thoracic vertebrae and pierce the crura of diaphragm and synapse with excitor cells in the ganglia of celiac plexus, renal plexus, and suprarenal medulla.
Sympathetic nervous system highlighting greater splanchnic nerve Lesser splanchnic nerves There are also right and left lesser splanchnic nerves. They are formed from the branches of tenth and eleventh thoracic ganglia sometimes twelfth also on both sides. They descend with greater splanchnic nerves and pierce the diaphragm to synapse the excitor cells in the ganglia of the lower part of celiac plexus. Manage consent. Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website.
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