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Monday, June 5, 2017

THE SYMPATHETIC NERVOUS SYSTEM: POINTS RELEVANT FOR THE ANESTHESIOLOGIST

🔸Posterior hypothalamus is the principal site of sympathetic nervous outflow.

🔸The sympathetic system has short preganglionic fibres and long postganglionic fibres

🔸The sympathetic nerves originate from columns of preganglionic neurons in the grey matter of the lateral horn of the spinal cord from the first thoracic segment down to the second or third lumbar segment.

🔸The preganglionic fibres leave the spinal cord through the ventral roots with the spinal nerves and then leave the spinal nerves as white rami communicantes ( myelinated B fibres ) to synapse with the postganglionic neurons in the ganglia of the sympathetic chain.

🔸The ganglia form sympathetic chains. The post-ganglionic fibres leave the ganglia as grey rami communicantes (unmyelinated C fibres) and join the spinal nerves or visceral nerves to innervate the target organ.

🔸In general, the preganglionic fibres secrete acetyl choline as neurotransmitter, while the post ganglionic ones secrete norepinephrine. The postganglionic sympathetic nerves that innervate the blood vessels of muscles, sweat glands and the hair follicles in the skin release acetylcholine instead of norepinephrine (noradrenaline).

➡️The sympathetic chains extend down the length of the vertebral column and are divided into four parts:

🔸A cervical part consisting of superior, middle and inferior galglia, supplying the head, neck and thorax. The superior cervical ganglion sends postganglionic fibres to form the internal carotid plexus. The inferior cervical or stellate ganglion is fused with the first thoracic ganglion.

🔸Branches of the thoracic part, from T 1 –T 5 supply the aortic, cardiac and pulmonary plexuses. The greater and lesser splanchnic nerves are formed from the lower seven thoracic ganglia. The lowest splanchnic nerve arises from the last thoracic ganglion and supplies the renal plexus.

🔸The coeliac plexus is derived from the lumbar sympathetic ganglia

🔸The sacral ganglia contribute to the hypogastric and pelvic plexus #TheLayMedicalMan

SYMPATHETIC SYSTEM PRODUCE:

🔸Dilatation of the pupil and retraction of the eyelid (levator palpebrae)

🔸Thoracic visceral effects of positive inotropic and chronotropic cardiac effects, pulmonary blood vessel vasoconstriction and bronchial smooth muscle relaxation.

🔸Abdominal visceral effects of increased sphincteric tone and inhibition of peristalsis, leading to relaxation of the gut and reduced motility.

🔸Pelvic visceral effects of relaxation of the bladder wall and the rectum with sphincter closure. Contraction of the smooth muscle of the seminal vesicles and prostate produces ejaculation. #TheLayMedicalMan

🔸Cutaneous effects such as piloerection, vasoconstriction and sweating.

🔸In the limbs, the arterioles to the skin constrict, whereas the skeletal muscle arterioles vasodilate.

#physiology , #anaesthesia

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