Autonomic Nervous System Basics for Med Students

Physiology for 1st year medical students A.N.S. “Written Questions” A.F.2023 A.F. 2021 1 ➢ Q. Autonomic is different from somatic (voluntary) motor nerves in: Somatic Autonomic controls Voluntary skeletal muscles involuntary = visceral: internal organs Afferent relay dorsal horn cells lateral horn cells. Efferent: Origin Anterior horn cells of S.C. lateral horn cells Eff. One neuron. Two neurons. Myelination Mostly myelinated -Pregang. : myelinated B - Postgang. : unmyelinated C ➢ Q. Autonomic Ganglia: • Ganglion: collection of neurons )postganglionic( outside CNS. • Function: distribution centers: Each preganglionic fiber synapse with 8-9 postganglionic neurons. Types: (1) Paravertebral (2) Collateral ganglia: (3) Terminal (4) adrenal medulla: sympathetic chain: ganglia: site on both sides of midway between origin and very near to - modified sympathetic vertebral column organ, at origin of big vessels organ Stimulation causes adrenaline (80%) and noradrenaline For sympathetic only Sympathetic mainly parasympathetic (20%) release into blood. N.B. ganglion for each - ciliary, sphenopalatine, and postganglionic segment of spinal cord otic are collateral are very short except cervical which parasympathetic ganglia. are three: superior, middle and inferior A.F. 2021 1 Origin Course Ganglia Functions of Sympathetic Nervous System (thoraco-lumbar) Q. Head and Neck Q. Thoracic Viscera Q. Abdominal Viscera Q. Pelvic Viscera T1,2 T 1-4 T 7-12 T12 & L 1-3 greater splanchnic n. lesser splanchnic n. in paravertebral chain Collateral cervical ganglia Functions 1- EYE: 1) Mydriasis (dilatation of pupil): 2) decrease power of lens to see far: relaxation of ciliary muscle 3) widening of palpebral fissure (increase field of vision) 4) exophthalmus (increase field) 5) VC 2- Skin: 1) Secretory to sweat glands. 2) Vasoconstriction 3) erection of hairs. 3- Salivary Glands: trophic secretion: conc. and viscid. 4-Cerebral circulation: flow increased: 1) rise of systemic ABP 2) cerebral vessels mildly constricted . 5- Brain: increase mental alertness A.F. 2021 cervical and upper 4 thoracic 1. Heart1) Increase all properties: Rate, force coeliac & superior mesenteric. 1. (GIT): - relaxation of wall - contraction of sphincters. 2. Liver: glycogenolysis 2) VD of coronaries ↑ blood glucose (indirect). 3. Spleen: Contraction: 2. Lungs: pouring blood - Dilatation of 4. Adrenal Medulla: bronchi. - adrenaline and - VC noradrenaline in blood 5. Blood vessels: VC 2 - inferior mesenteric 1. GIT: • relaxation of wall • Contraction of internal anal sphincter 2. Urinary Bladder: - relaxation of wall. - Contraction of internal urethral sphincter. 3. Male genital: VC (shrinkage of penis). ejaculation 4. Female genital: Variable effects Origin Course Ganglia Functions A.F. 2021 Oculomotor (III): ciliary 1) Miosis (pupil constriction): Contraction increase power of lens: Contraction of ciliary muscle for near vision Functions of Parasympathetic Nervous System (cranio-sacral) Q. Head and Neck Q. Thoracic & Abdominal Viscera Facial (VII): Glossopharyngeal vagus nerve (X ) (IX): 1) Some in terminal sphenopalatine otic supply parotid 1. Heart: ganglion: gland: secretion and - Inhibition of all properties of supply lacrimal vasodilator atria only and nasal - does not supply the ventricles glands. - ↓ coronary flow. (indirect). 2) Other fibers run 2- Lungs to - Broncho-Constriction submandibular - Dilatation of blood vessels. ganglion: 3. GIT: supply - contract wall submanadibular - relax sphincters and sublingual - Secretory to GIT glands. salivary glands 4. On Gall Bladder: evacuation: • secretion and contract to wall and relax sphincter vasodilator. of Oddi 3 Q. Pelvic Viscera S2,3,4 pelvic nerve terminal 1-Defecation: contraction of wall of rectum and relaxation of internal anal sphincter. 2. Micturition: contraction of wall of bladder and relaxation of internal urethral sphincter. 3. Erection: VD of penis. 4. Female genital: VD. Chemical Transmission at Autonomic junctions I. Q. Acetylcholine II. Q. Noradrenaline (Norepinephrine) Sites of 1) All preganglionic fibers: sympathetic & parasympathetic Postganglionic sympathetic fibers, except: release 2) All postganglionic parasympathetic fibers. 1. to sweat glands 3) Some postganglionic sympathetic fibers: 2. to the blood vessels of skeletal muscles • to sweat glands. • to blood vessels of skeletal muscles. Release: - action potential spreads over terminal fibers “exocytosis” - calcium diffuse into nerve terminals → exocytosis. Removal acetylcholine esterase: 1) Re-uptake: - by active transport (50-80%). true pseudo 2) Diffusion: to surrounding fluids then blood. specificity specific non-specific 3) Destruction by enzymes such as: affinity great less 1. M.A.O. (deamination): site nerve endings plasma 2. C.OM.T. (methylation): A.F. 2021 4 ➢ RECEPTORS A. Q. Cholinergic: I. nicotinic (nicotine activated): in autonomic ganglia II. muscarinic (muscarine activated): in organs B. Q. Adrenergic: On effector organs Alpha Beta 1 2 1 2 Mechanism ↑ intracellular decreasing increasing c-AMP of Action Ca++. c-AMP Actions • Vasoconstriction. • Vasodilatation • Contraction of : • Inhibition of muscle of: - Sphincters of G.I.T. -Bronchioles - Spleen. -Urinary bladder. - Internal urethral • ↑ HR & force of sphincter. contraction of heart (B1) • Inhibition of • Metabolic: Lipolysis . muscles of intestine. Glycogenolysis Q. Drugs affecting A.N.S receptor nicotinic Increase activity: 1. Nicotine small dose Decrease activity: 1) Nicotine large dose muscarinic adrenergic Muscarine 1. Stimulate alfa: Phenylephrine 2. Stimulate beta: Isoprenaline Atropine 1) block alfa: phentolamine 2) block beta: propranolol A.F. 2021 5