Clinical Neuroanatomy Made Ridiculously Simple - Part 3

Clinical Neuroanatomy Made Ridiculously Simple - Part 3 -...

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CHAPTER 6. AUTONOMIC SYSTEM AND HYPOTHALAMUS The autonomic system regulates glands, smooth muscIe and cardiac mus- cle. It contains sympathetic and parasympathetic components. The sym- pathetic system as a whole is a catabolic system, expending energy, as in the flight or fight response to danger, e.g. increasing the heart rate and contra- ctility and shunting blood to the muscles and heart. The parasympathetic system is an anabolic system, conserving energy, e.g. in slowing the heart rate and in promating the digestion and absorption of food. The cell bodies of preganglionic sympathetic fibers lie in the iniermediola~u/ columns of the spinal cord at spinal cord levels TI-L2 pigs. 45,461. Those of the para- sympathetic system occupy comparable positions at spin J cord levels 32-S4. D RSAL ROOT GANGLION 4 PERIPHERAL NERVE 'PARAVERTEBRAL GANGLION cAcEwL wmcW Fig. 45 A. The sympathetic nerve routes. B. parasympathetic nerve routes.
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Fig. 46 %hematic view of the au~osamic nervoussystem. In addition, cranial nerves 3.7.9 and 10 have parasympathetic components (3 - pupil and ciliary body constriction; 7 - tearing and salivation; 9 - salivation; I0 - the vagus and its ramifications). In order to extend all over the body the sympathetic system fibers leave the spinal cord at levels TI-L2, enter the paravertebral ganglion chain and then may travel up or down the chain for considerable distances prior to synapsing (Fig. 46). The sympathetic chain stretches from t he foramen mag- num to the coccyx and supplies the far reaches of the My with post-ganglionic sympathetic fibers. Parasympathetic fibers reach widespread areas via the vagus pig. 46). Bath parasympathetic and sympathetic systems contain two neurons be- tween the spinal cord and periphery. The first synapse is cholinergic (con- taining acetylcholine). For the sympathetic system this synapse is either in the paravertebral chain of sympathetic ganglia or farther away in the pre- vertebral ganglion plexuses (Fig. 45A). Parasympathetic synapses typically lie very close or within the viscera. The final synapse the parasympathetic system contains acetylcholine,
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whereas the final synapse of the sympathetic system contains noradrendine, with the exception of certain synapses, as for sweating, that contain acetylcholine (i-e., are cholinergic). In the chart below, note that secretory function in general are stimulated by cholinergic fibers. Shuchlre Sympathetic function PamsynapatRetic~unctlofi EY e Dilates pupil (mydnasis) Contracts pupil (m~osis) No significant effect on contracts c111ary mul;cIc cilrary muscle (accommodation) Lacrimal gland significant effect Shmulntes secrelion Salivary glands significant effect Stimulates secretion Sweat Hem Rate Farce of ventricular contraction Blood vessels Lungs Stimulates secretion (cholinergic fibs) Increases Dilates or constricts cardiac & skeletal muscle vesselss Consnicts skin and digestive sysiern blood vessels Dilates bronchial tubes Inhibits motility and secretion No significant effect Decreases Decreases No significant effect Constricts bronchial tubes
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Clinical Neuroanatomy Made Ridiculously Simple - Part 3 -...

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