The preganglionic fibres of the sympathetic nervous system arise from the cell bodies spanning from the Thoracic (T1) to the Lumbar (L2) part of the spinal cord.
The Sympathetic Nervous System is made up of the following parts:
Sympathetic Trunks : These represent a pair of long cords located on either side of the vertebral column. They extend from the foramen magnum to coccyx. Every sympathetic trunk comprises of 21 lateral or chain ganglia (3 cervical, 12 thoracic, 5 lumbar and 1 sacral) interconnected to each other in a sequential manner. Every ganglion is a collection of neuronal cell bodies. A white ramus communicans connects the ganglia to the spinal cord while a grey ramus communicans connects the ganglia to the spinal nerve.
Preganglionic Sympathetic Fibres : These fibres are small sized neuronal axons located along the lateral funiculus of the spinal cord. These fibres generally exit frow the ventral root of the spinal nerves and forms synapses with neuronal dendrons located along all the thoracic and upper three lumbar chain ganglia, thus forming thoracolumbar outflow.
Postganglionic Sympathetic Fibres : These fibres are long sized neuronal axons of chain ganglia. Their effect is widespread as they innervate the smooth muscles and glands of visceral organs such as the heart, ciliary muscles and iris of eyes, lungs, gut, liver, urinary, and reproductive systems.
Collateral Ganglia : Three collateral ganglia are present namely, collateral ganglia coeliac, superior, mesenteric, and inferior mesenteric ganglia. Postganglionic fibres spread from neurons of collateral ganglia to visceral organs.
In general, the nerve endings of postganglionic fibres of sympathetic nervous system release adrenaline or nor-adrenaline; therefore are also known as adrenergic nerve fibres.
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