From Ganfyd
| Sympathetic nervous system
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 The right sympathetic chain and its connections with the thoracic, abdominal, and pelvic plexuses. (After Schwalbe.)
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| Function:
| Autonomic regulation
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| Search for Sympathetic nervous system in Gray's.
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The nerves that innervate smooth muscle and undertake autonomic function. They are mainly arranged in two chains of sympathetic ganglia either side of the vertebral bodies. Derangements of the sympathetic nervous system occur by direct trauma (including encroachment/disruption by malignancy) or by any generalised (poly-)neuropathy (typically Diabetes mellitus).
Innervates
- Smooth muscle coat of all blood vessels (except interior of brain)
- Mainly vasoconstrictor
- Important in maintaining systemic blood pressure and in distribution of blood flow to different vascular beds
- Eccrine sweat glands
- Pineal gland
- Heart
Fine Structure
Lateral sympathetic ganglia of abdomen
Posterior sympathetic ganglia of abdomen
- Lie close to central axis of body
- In 2 'sympathetic chains' (paravertebral ganglia)
- Unpaired prevertebral ganglia surrounding bases of great arteries
- Aortico-renal ganglia (renal arteries)
- Pelvic ganglia (short adrenergic neurones)
- Chromaffin cells of adrenal medulla (innervated by preganglionic sympathetic neurones)
Preganglionic neurones
- Lie within 12 thoracic and upper 2-3 lumbar segments of spinal cord
- In lateral horns of grey matter
- Small (1-4mm) myelinated (B) fibres
- Leave by ventral roots of T1 to L3 and run to sympathetic chain as white rami communicantes
- Fibres run in sympathetic chain and terminate on ganglia there or leave as splanchnic nerves to terminate on prevertebral ganglia and adrenal medulla
- Thoracic splanchnic nerves (T5-T12) are subpleural
Ganglionic neurones
- Outnumber preganglionic and each preganglionic innervates a number of ganglionic neurons
- Each ganglionic neurone may recieve input from up to 10 or more preganglionic fibres
- Vasomotor and sudomotor controlled separately
Postganglionic axons
- Relatively long, unmyelinated, <1mm in diameter (C fibres)
- Mostly adrenergic
- Exception is eccrine sweat glands which are cholinergic
- Travel in mixed spinal nerves or along blood vessels
Pathologies
- Disruption of the sympathetic supply in the neck leads to Horner's syndrome, one cause of which is spread of an apical lung tumour(Pancoast's tumour).
- Occasionally sympathectomy can be performed surgically in an attempt to control hyperhidrosis of specific areas (the upper limbs can be amenable to this approach).
- Diabetes mellitus can lead to a general autonomic neuropathy in which the control of blood pressure is though to be lost through ineffective sympathetic supply to more distal blood vessels
