🔸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.
🔸’BASIC CIRCUIT’ : PREGANGLIONIC NEURONS in the grey matter of the lateral horn of the spinal cord (from T1-L3 segment) –> they 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)–> they then synapse with the POSTGANGLIONIC NEURONS in the GANGLIA OF THE SYMPATHETIC CHAIN –> These ganglia together will form sympathetic chains –> The POSTGANGLIONIC NEURONS 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 UNIQUE EFFECTS:
DILATATION / RELAXATION
✔️Bronchial smooth muscle
✔️Gut, Urinary bladder (sphinctors constrict)
✔️Skeletal muscle arterioles (Post ganglionic transmitter: ACh)
CONSTRICTION / SECRETION
✔️Levator Plapabrae Superioris
✔️Piloerection hair follicle (Post ganglionic transmitter: ACh)
✔️Muscles of seminal vesicles(ejaculation)
✔️Sweat glands (sweating) (Post ganglionic transmitter: ACh)
#physiology , #anaesthesia