Lecture 13 Parasympathetic-2 Notes PDF

Faculty of Medicine Academic Year: 2024-2025 Year: 1 Semester 1 : Human Body Function (HBF) Module: 102  PARASYMPATHETIC NERVOUS SYSTEM- II By: Dr. Mohamed abo El Hassan Dr. Ramadan Saad Dep...

Faculty of Medicine Academic Year: 2024-2025 Year: 1 Semester 1 : Human Body Function (HBF) Module: 102  PARASYMPATHETIC NERVOUS SYSTEM- II By: Dr. Mohamed abo El Hassan Dr. Ramadan Saad Department Department of Clinical physiology : 12/6/2024 2 2  Objectives o Describe the functions of the parasympathtic cranial nerves (VII Facial, IX Glossopharyngeal, and X Vagus). oDescribe the functions of the sacral part of the parasympathetic nervous system. o Illustrate the relationship between the sympathetic and parasympathetic nervous systems. o Compare the functions of sympathetic and parasympathetic systems. 3  Origin of Parasympathetic N.S. FROM Nuclei of the 3rd, 7th, 9th & 10th cranial nerves, in the brain stem (Cranial outflow) & The lateral gray horn of S2-S4 segments of spinal cord (Sacral outflow) so it is called CRANIO- SACRAL OUTFLOW  Cranial outflow Preganglionic fibers from cranial outflow are carried by 3rd, 7th, 9th & 10th cranial nerves and terminate in ciliary, pterygopalatine, submandibular, otic & peripheral ganglia Postganglionic fibers innervate organs of the head, neck, thorax, and abdomen VII- Facial nerve Origin and Relay : It arises from superior salivary nucleuss in pons and relays in the spheno-palatine ganglion. “Superficial petrosal nerve”. Functions: - To lacrimal glands leads to secretion of tears. - To mucous glands of nose, mouth, pharynx & palate lead to increase mucous secretion. - Vasodilatation (VD) of their blood vessels. Chorda tympani N. (branch of facial - Chorda tympani N. (branch of facial nerve) - Relay: in the submandibular ganglion. - Postganglionic fibers pass to: 1. Submandibular & sublingual salivary glands causing true salivary secretion (large in volume, watery & poor in organic substances). 2. Blood vessels of salivary glands, anterior 2/3 of the tongue to cause vasodilatation (VD).  VD of tongue blood vessels Anterior Posterior 2/3 of 1/3 Of tongue tongue VII IX  IX- Glossopharyngeal nerve Origin and Relay: It arises from inferior salivary nucleus in medulla oblongata relays in optic ganglion in the otic ganglion. Functions: 1. To the parotid salivary gland causing true secretion. 2. To the blood vessels of the salivary gland & posterior 1/3 of the tongue causing vasodilatation (VD). Parasympathetic to thorax & abdomen X. Vagus nerve Origin and Relay: It arises from dorsal nucleus in medulla oblongata and relays in terminal ganglia present in the thoracic & abdominal viscera. Functions: - It represents 75 % of all the parasympathetic supply. 12  1- In the thorax (A) In the heart: - Inhibition of all cardiac properties (decrease conductivity, contractility, excitability & rhythmicity). - Vasoconstriction (VC) of coronary blood vessels (decrease blood flow to the cardiac muscle). N.B. Parasympathetic stimulation produces V.D. allover the body except in the coronary vessels (where it causes V.C.): (B) In the lungs: - Contraction of smooth muscles of the bronchi & bronchioles (broncho-constriction). - Increase mucous secretion. - Vasodilatation (VD) of pulmonary blood vessels.  2- In the abdomen  Gastro-intestinal tract (G.I.T.): 1. Smooth muscles: - Contraction of the wall of esophagus, stomach, small intestine & proximal part of the large intestine and relaxation of their sphincters. Therefore, parasympathetic stimulation promotes deglutition (swallowing) as well as evacuation of food from the GIT. 2. Secretory to the gastric glands: - Increases HCL & mucous secretion. 3. Blood vessels: Vasodilatation (VD). The liver: 1. Stimulate bile secretion. 2. Contraction of gall bladder wall & relaxation of sphincter of Oddi leads to its evacuation.  The pancreas: 1. Secretion of pancreatic juice rich in enzymes. 2. Stimulates insulin secretion by B-cells. WHY IT'S CALLED VAGUS ? Because it has :- 1- Afferent & efferent 2- Stimulatory & inhibitory 3- Widely distributed  Sacral outflow Preganglionic fibers arises from the LHCs of 2, 3 & 4 sacral segments and carried by pelvic splanchnic nerves to terminal ganglia in pelvis where they synapse. Postganglionic fibers innervate organs of the pelvis and lower abdomen  II- SACRAL DIVISION OF PARASYMPATHETIC Origin: LHCs of S 2,3 & 4 and it is called (Pelvic nerve). - Relay: terminal ganglia called hypogastric ganglia.  Parasympathetic to the pelvis (Pelvic nerve) - Functions: 1. Urinary bladder: Contraction of the wall & relaxation of the internal urethral sphincter. So, it helps micturition. 2. Rectum & anal canal: Contraction of the wall & relaxation of the internal anal sphincter. So, it helps defecation. 3. seminal vesicles and prostate → stimulate its secretions 4. Sex organs: VD of blood vessels organs → erection by vasodilatation of blood vessels of penis (♂) or clitoris (♀) and shares in the execution of sexual act. MICTURATION: - Pelvic nerve causes contraction of wall of urinary bladder and relaxation of internal uretheral sphincter → passage of urine DEFECATION : - Pelvic nerve causes contraction of wall of rectum and relaxation of internal anal sphincter → passage of stool N.B External uretheral or anal sphincters are not under autonomic control but under somatic control via pudendal nerve. N.B Internal sphincter is more important than external sphincter because it is smooth muscle i.e fatigue resistant, while external sphincter is skeletal muscle i.e fatigable.  Summary to parasympathetic activity  “Rest and digest” responses, which include: 1. Decreased metabolic rate 2. Decreased heart rate and blood pressure 3. Increased secretion by salivary and digestive glands 4. Increased motility and blood flow to the digestive tract 5. Stimulation of urination and defecation  Also called the anabolic system—increases nutrients in blood Growth and development Excess stored as lipids or glycogen for energy reserve  What is the Relation between Sympathetic & parasympathetic systems - Usually there is antagonistic relation: as in heart , lungs & pelvis. - Sometimes, the relation is synergistic (each system help the other) as in salivary secretion: Sympathetic produces trophic secretion while parasympathetic produces true secretion. -There is complementary action during sexual intercourse. The parasympathetic causes erection and the sympathetic causes ejaculation in males & orgasm in females. Contrast between Sympathetic & Parasympathetic Systems 24 parasympathetic sympathetic 25 26 27  INTERACTIVE QUESIONS 1) About the vagus nerve, all the following is true except: a. It originates mainly from medulla oblongata. b. It contains parasympathetic pregans.Fibres. c. It has no direct effect on ventricular contraction. d. It causes increased peristaltic movements of the intestinal wall. 2) Stimulation of the pelvic nerve (sacral autonomic) produces: a. Relaxation of the wall of rectum & contraction of the internal anal Sphincter. b. V.C. of the blood vessels in the external genitalia causing erection of penis. c. Contraction of smooth muscles in the male sexual passages causing ejaculation. d. Relaxation of the internal urethral and anal sphincters. 28 3) Sympathetic tone: a. In initiated by exposure to stress b. Determines heart rate at rest c. Controls the level of arterial blood pressure d. Is increased by use of a ganglion blocking drugs 4) Vagal tone on the heart: a. Increases the heart rate b. Weakens contraction of the atrial muscle c. Is blocked by use of a muscarinic receptor agonist d. Decreases during rest 29  References Linda S. Costanzo HBF - 102 30 30