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ANS comprises of Parasympathetic and Sympathetic divisions.
Parasympathetic Nervous system Click to view the animation...
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Craniosacral outflow - Preganglionic fibres originate in the midbrain ( 3rd (oculomotor) cranial nerve), medulla oblongata (7th (facial), 9th (glossopharyngeal) and 10th (vagus) cranial nerves) and 2nd - 4th segments of sacral spinal cord.
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Preganglionic fibres are long and usually synapse on or within the target organ in the ciliary ganglion (3rd cranial nerve), submandibular ganglia (7th cranial nerve) otic ganglion (9th cranial nerve), terminal ganglia in the heart, lungs, liver, spleen, GI tract, kidney (10th cranial nerve)
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Innervation is discrete, with preganglionic to postganglionic ratio of 1:1
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Postganglionic fibres are short and innervate target organs:
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cranial division innervates the eye, salivary glands, heart, bronchi, gastrointestinal tract
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sacral division innervates bladder, colon, urinary and rectal sphincters and genital organ
Sympathetic nervous system Click to view the animation...
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Thoracolumbar outflow - preganglionic fibres originate in the intermediolateral columns of spinal cord from the 1st thoracic to the 3rd lumbar vertebrae
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Preganglionic fibres are short and usually synapse well before the target organ in either:
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Vertebral (Paravertebral) ganglia which include the cervical ganglia, consisting of 22 pairs on either side of vertebral column
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Prevertebral ganglia in abdomen (celiac, cranial and caudal mesenteric)
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Innervation is diffuse, with preganglionic to post ganglionic ratio upto 1: 20
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Postganglionic fibres are long and innervate target organs
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Fibres from vertebral ganglia innervate blood vessels, the eyes, salivary glands, heart, bronchi, sweat glands and hair follicles.
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Fibres from prevertebral ganglia innervate the stomach, intestine, bladder, urinary and rectal sphincters and genital organs.
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Adrenal medulla is embryologically and functionally a sympathetic ganglion; innervated by typical sympathetic preganglionic neurons
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