Lecture:12 Dr. Eyad M. Hussein Anatomy and Physiology of Sympathetic Nervous System Dr. Eyad M. Hussein Ph.D of Neurology Consultant in Neurology Department, Nasser Hospital, Assistant Professor, Faculty of Medicine, Islamic University Faculty of Dentistry, University of Palestine

Comparison of Autonomic and Somatic Nervous System

The Sympathetic Nervous System Cells of Origin: The sympathetic NS formed by the cells of the intermediolateral nucleus of the lateral horn of all thoracic and upper 2 lumbar segments of the spinal cord “T1-L2” (Thoraco-lumbar part) and reach the sympathetic chain by the white rami (right and left). Sympathetic cells may also be found in C8 segments of the spinal cord.

The Sympathetic Ganglia Paravertebral Ganglia: which formed the sympathetic chain or trunk. There are two sympathetic chains (right and left) on each side of the vertebral column. Each chain extends from the level of the first cervical vertebra (above) to front of the coccyx (below) where two chains unite to form a single coccygeal ganglion (impar ganglion). It formed of 22-23 ganglia on each side. 2. Collateral or Peripheral Ganglia: these are ganglia that surround some large arteries: celiac, superior and inferior mesenteric ganglia.

How Many Sympathetic Ganglia are Found in the Sympathetic Chains? Cervical ganglia: 3 pairs. Thoracic ganglia: 10-12 pairs. Lumbar ganglia: 4-5 pairs. Sacral ganglia: 4-5 pairs. Coccygeal ganglion: one fused together (impar ganglion).

The Preganglionic Sympathetic Fibers They are short and myelinated fibers (white fibers). The 14 preganglionic fibers leave the spinal cord along the anterior nerve roots of all thoracic and upper 2 lumbar spinal nerves → nerve trunk → ventral rami → then the preganglionic fibers leave the ventral rami via 14 white communicants rami to reach the ganglia of the sympathetic chain.

The Postganglionic Sympathetic Fibers (PSF) They are long and non-myelinated fibers (gray fibers). They leave the sympathetic trunk to reach the organs

I. The Cervical Part of the Sympathetic Chain Site: It lies behind the common, external, and internal carotid arteries, outside carotid sheath and medial to the vagus nerve. It has: Preganglionic fibers: from upper thoracic segments (T1-T4) until the three cervical ganglion. Postganglionic fibers: leave these ganglia, to the cervical nerves and to cranial nerves.

The Cervical Sympathetic Ganglion There are three cervical sympathetic ganglion: Superior cervical sympathetic ganglion. Middle cervical sympathetic ganglion. Inferior cervical sympathetic ganglion.

The Superior Cervical Sympathetic Ganglion It is the largest cervical sympathetic ganglion (about 2-3 cm long). Site: lies behind the internal carotid artery. Its continuation upwards inside the skull is called the internal carotid nerve or plexus. Branches: Gray rami: to upper 4 cervical nerves. Communicating branches: to the cranial nerves (IX, X, XII nerves). The internal carotid branch. The external carotid branch. The pharyngeal branch: to form part of the pharyngeal plexus. The superior cervical cardiac sympathetic branch: to the heart.

The internal carotid branch: passes upwards to form the internal carotid plexus around the internal carotid artery which gives the following branches: Branches to join III, IV, V, and VI cranial nerves. Branches to the pituitary gland. Deep petrosal nerve: joins the greater petrosal nerve to form nerve to pterygoid canal (to pterygopalatine ganglion). Sympathetic root of ciliary ganglion. Long ciliary nerve: supplies the dilator pupillae muscle. The external carotid branch: passes to the external carotid artery to form an external carotid plexus to supply salivary glands (parotid, submandibular and sublingual salivary glands) via the otic and submandibular ganglia.

Destruction of the Superior Cervical Sympathetic Ganglion This removes all the sympathetic fibers that reach face and neck and produces Horner’s syndrome: Myosis. Partial ptosis. Anhydrosis. Enophthalamus.

The Middle Cervical Sympathetic Ganglion Site: lies behind the common carotid artery at the level C6 vertebra. Branches: Gray rami: to the 5th and 6th cervical nerves. The middle cervical cardiac sympathetic branch: to heart. Inferior thyroid branches: to the thyroid gland. Subclavian branch: around subclavian artery.

The Inferior Cervical Sympathetic Ganglion Site: lies behind the common carotid artery and the lower part of the vertebral artery at the level C7 vertebra. The inferior cervical ganglion may fuse with the first thoracic ganglion to form one ganglion called Stellate or Cervicothoracic ganglion. Branches: Gray rami: to 7th and 8th cervical nerves. The inferior cervical cardiac sympathetic branch: to heart. Vertebral branch: it form a vertebral sympathetic plexus around the vertebral artery. Subclavian branch: around subclavian artery.

II. Thoracic Part of the Sympathetic Trunk Ganglia: 10-12 ganglia (usually 11 ganglia), because the T1 ganglion may fuse with the inferior cervical ganglion. Branches: Supply: Blood vessels, sweat glands and the muscle of hairs (arrector pili muscles) of a skin segment of the body. Thoracic aorta. Heart. Bronchi and lungs. Stomach, liver, gall bladder, pancreas and spleen. Small intestine, ascending colon and right 2/3 of the transverse colon. Kidney and upper part of the ureter.

III. Lumbar Part of the Sympathetic Trunk Ganglia: 4 - 5 ganglia. Branches: supply many visceral structures in the abdomen and pelvis: Gives fibers to lumbar nerves. Left 1/3 of transverse colon, descending colon and pelvic colon. Urinary bladder, rectum and genital organs. Abdominal aorta.

IV. Pelvic Part of the Sympathetic Trunk Ganglia: 4 - 5 ganglia. Branches: supply mainly visceral structures in the pelvis: Gives fibers to all sacral and coccygeal nerves. They join the pelvic plexuses to supply the urinary bladder, rectum and genital organs. Form a plexus around the sacral vessels.

Sympathetic Supply of the Pupil Pathway: Fibers start from hypothalamus, descends through the brain stem and cervical part of the spinal cord to the lateral horn cells of C8 – T2 segment → preganglionic fibers → sympathetic chain → relay in the superior cervical sympathetic ganglion. The postganglionic fibers pass with carotid plexus (around ICA) → long ciliary nerve → dilator pupillae muscle.

Innervation of the Urinary Bladder and Rectum They receive 3 types of nerves: Somatic innervation (Pudendal nerve): supplies the striated muscles of the external sphincter of the urethra and anus. Sympathetic nerves: branches from the pelvic plexuses. They supply the blood vessels of the urinary bladder and rectum. Parasympathetic nerves: branches from S2, S3 & S4 segments of the spinal cord → pass in S2, S3 & S4 → pelvic plexuses. They supply: The muscles of the walls of urinary bladder and rectum (contraction). Inhibitory fibers to the internal sphincter of the urinary bladder and rectum (relaxation) → to allow micturition and defecation.

Autonomic Reflexes in the Spinal Cord Evacuation reflex for emptying the bladder (micturition reflexes) and colon (defecation reflexes). Micturition reflexes: distension of the bladder results in reflex contraction of bladder wall and relaxation of urethral sphincters (center S2, S3, S4). Defecation reflexes: distension of the rectum results in reflex contraction of the rectal wall and relaxation of the anal sphincters (center S2, S3, S4). Changes in vascular tone, resulting from local skin heat and cold. Sweating, which results from localized heat on the surface of the body.

Seminal Ejaculation It produced by sympathetic stimulation. Stimulation of the sympathetic nervous system produces: Contraction (stimulation) of seminal vesicles and ejaculatory duct. Relaxation (inhibition) of the muscles of the wall of urinary bladder. Contraction of the internal sphincter of urethra. In this way ejaculation of seminal fluid is produced, and at the same time micturition is inhibited and reflux of seminal fluid into the urinary bladder is avoided.

Effects of Autonomic Nervous System on Organs and Body Sympathetic action Parasympathetic action Eye: Pupil Ciliary muscle - Dilates - Relaxes - Constricts - Contracts Glands: Lacrimal & nasopharyngeal glands Salivary glands - Reduces secretion - Vasoconstriction - Increase secretion Heart - Heart rate & muscle contraction increased - Heart rate & muscle contraction decreased Lung: Bronchial muscle Bronchial arteries - Dilates bronchi - Constricts bronchi GIT: Muscle in walls Muscle in sphincters Glands - Decreases peristalsis - Reduce secretion - Increases peristalsis - Increases secretion Kidney - Decreased urine secretion - Increased urine secretion Urinary bladder: Bladder wall Sphincter

Parasympathetic action Organ Sympathetic action Parasympathetic action Gall bladder - Relaxation Contraction Liver - Increased conversion of glycogen to glucose - Stimulate release of bile Pancreas - Inhibition of insulin and glucagon secretion - Stimulation of insulin and glucagon secretion Male sex organs - Ejaculation - Erection Pineal gland - Increase melatonin synthesis and secretion - Skin: Sweat glands Pilomotor muscle Increases secretion Platelet Increase aggregation lypolisis - Increase Renin secretion Mast cells: histamine Decrease

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