Pai

The autonomic nervous system, sympathetic chain and stellate ganglionJohn Craven

AbstractThe anatomy of the parasympathetic and sympathetic nervous systems

and the distribution of their fibres are described in this article. The clini-

cal effects of blockage by local anaesthetic are listed.

Keywords autonomic plexuses; parasympathetic nervous system;

sympathetic nervous system; sympathetic trunk; vagus nerve

The autonomic nervous system supplies viscera, glands, and smooth and cardiac muscle. The two complementary parts of the autonomic nervous system (sympathetic and parasympathetic) leave the CNS at different sites and usually have opposing effects on the structures they supply through endings that are mainly adrenergic or cholinergic. The sympathetic system prepares the body for ‘fight or flight’ and the parasympathetic system controls its vegetative function. There are also afferent fibres, which can convey visceral sensations such as ischaemia.

Sympathetic system

In the sympathetic system, preganglionic fibres arise from the lateral columns in segments T1–L2, passing for a short distance in the anterior roots of the corresponding spinal nerves before leaving as white, myelinated, rami communicantes to join the sympathetic trunk (Figure 1).

The paired sympathetic trunks consist of ganglia and nerve fibres, and extend along the prevertebral fascia from the base of the skull to the coccyx. There are three cervical (upper, middle and lower), eleven thoracic, four lumbar and four sacral ganglia, and from each pass fibres to somatic and visceral structures (Figure 2).

Somatic fibres are distributed as grey, non-myelinated, post-ganglionic rami communicantes to each of the 31 spinal nerves and supply vasoconstrictor fibres to arterioles, secretory fibres to sweat glands, and pilomotor fibres to the skin. Grey fibres, unlike the white preganglionic fibres, do not run up or down the sympathetic trunk.

Visceral fibres pass to the:• thoracic viscera by postganglionic fibres to the cardiac,

oesophageal and pulmonary plexuses• abdominal viscera by preganglionic splanchnic nerves

John Craven, FRCS, was formerly Consultant Surgeon at York Hospital,

York. He is past chairman of the primary examiners of the Royal

College of Surgeons of England.

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n

• adrenal medulla by the preganglionic greater splanchnic nerve

• cranial and facial structures that accompany the carotid ves-sels, larynx and pharynx via postganglionic fibres from the middle cervical ganglion.

The stellate ganglion: in 80% of the population, the inferior cervical ganglion is fused with the first thoracic ganglion to form the large stellate ganglion, which lies on the neck of the first rib behind the cervical pleura. Its branches are conveyed by grey (non-medullated) rami communicantes to the C7, C8 and T1 spinal nerves and, via a plexus, to the subclavian artery and its branches, from where they are distributed to the upper limb. It is of clinical significance that the sympathetic nerve supply of the pupil and levator palpebrae superioris can be blocked by local anaesthetic injection or tumour invasion (Pancoast’s tumour), both producing a Horner’s syndrome.

The thoracic sympathetic trunk comprises 11–13 ganglia and gives branches to all the corresponding spinal nerves; the first forms part of the stellate ganglion. Visceral branches pass from the upper six ganglia to the pulmonary and cardiac plexuses and three splanchnic nerves. The greater splanchnic nerve (T5–T10) ends in the coeliac plexus, the lesser (T9 and T10 or T10 and T11) in the aortic plexus and the lowest in the renal plexus.

The coeliac plexus lies around the origin of the coeliac artery and is formed from the greater splanchnic nerve and post-ganglionic fibres of L1. It is continuous with the network of sympathetic nerves on the aorta, the aortic plexus, the branches of which accompany the branches of the aorta. It can be blocked with local anaesthetic or neurolytic solutions in the treatment of upper gastrointestinal pain.

The lumbar sympathetic trunk usually comprises four ganglia in each trunk. Its branches pass to the coeliac and hypogastric plexuses, and to each of the lumbar spinal nerves. Blockade of these ganglia can be useful for some pain conditions of the lower limbs and ischaemia due to small vessel disease.

The hypogastric plexuses supply the pelvic viscera. The superior plexus receives branches from the coeliac plexus and the

Sympathetic reflex arc

Lateral horn

Preganglionic fibres

White ramus communicans

Autonomic ganglion in sympathetic trunk

Afferent neuron

Grey ramuscommunicans

Figure 1

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Pain

The autonomic nervous system

Ga

ng

lia

Gla

nd

s

Ciliary

Sphenopalatine

Submandibular

Otic

Eye

Lacrimal

Nasal

Submandibular

Sublingual

Parotid

Heart

Bronchi

Lungs

Oesophagus

Liver

Pancreas

Bladder

Genitalia

Descending colon

Rectum

Kidneys

S4S3

S2

T12

T1

XIX

VII

III

Parasympathetic Sympathetic

Tarsal muscles

Dilator pupillae

Hypophysis

Vessels

Sweat glandsHead and neck

Thyroid gland

Bronchi and lungs

Oesophagus

Stomach

Small gut

Large gut

Suprarenal gland

Kidney

Bladder

Genitalia

Descending colon

Rectum

Heart

Figure 2

sympathetic trunks and its efferent fibres mainly travel in two hypogastric nerves descending on each side of the rectum, sup-plying the rectum, bladder and genitalia. The plexus receives autonomic sensory fibres of pain and bladder and rectal disten-sion, from the pelvic viscera. The inferior plexus also receive parasympathetic branches from the nervi erigentes (S2–S4).

Parasympathetic system

The parasympathetic system is much smaller than the sym-pathetic system and comprises a cranial and sacral component on each side. Its actions contrast with those of the sympathetic system and include constriction of the pupils, decrease in the rate and conduction of the heart, bronchoconstriction, an increase in peristalsis, sphincter relaxation and an increase in glandular secretion. Its pelvic component inhibits the internal sphincter of the bladder and it is stimulatory to the detrusor muscle of the bladder. Its medullated preganglionic fibres are much longer than those of the sympathetic system and synapse

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with postganglionic cells close to, or in the walls of, the viscera they supply.

The cranial outflow is conveyed in the oculomotor (III), facial (VII), glossopharyngeal (1X) and vagus nerves (X). The latter is the largest component and most widely distributed. The para-sympathetic nerves of the cranial nerves III, VII and IX are trans-mitted via four ganglia through which also pass sympathetic and somatic fibres.• The ciliary, lateral to the optic nerve, from which pass post-ganglionic fibres to sphincter pupillae and ciliary muscles.• The sphenopalatine in the pterygopalatine fossa is supplied by fibres from the greater petrosal branch of the facial nerve; post-ganglionic fibres supply the lacrimal gland, nasal and pharyngeal glands.• The submandibular ganglion receives fibres from the facial nerve through the chorda tympani branch and via the lingual nerve, which lies on the hypoglossus muscle. Preganglionic fibres pass in the lingual nerve to supply the submandibular and sublingual salivary glands, and oral and pharyngeal glands.

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Pain

• The otic ganglion receives fibres from the glossopharyngeal nerve via the tympanic plexus and the lesser petrosal nerve; postganglionic fibres pass in the auriculotemporal nerve to the parotid gland.

The parasympathetic supply of the thorax, abdomen and pel-vis is derived from the vagi and pelvic splanchnics. The anterior and posterior vagal trunks are distributed through the coeliac

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plexus along the branches of the aorta to the alimentary tract and its derivatives as far as the splenic flexure. The pelvic splanchnic nerves (S2, S3, S4) pass to the hypogastric and pelvic plexuses. From the former, branches pass along the inferior mesenteric artery to supply the gut distal to the splenic flexure; from the latter are supplied the pelvic viscera. Their action helps in micturition and defecation by relaxing the bladder and bowel sphincters. ◆

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