Autonomic Nervous System - Chemical Transmission Lecture Notes PDF

THE AUTONOMIC NERVOUS SYSTEM CHEMICAL TRANSMISSION BY PROF. A. EMAD OMAR ZAKI FALL 2024 CHEMCAL TRANSMISSON  CHEMICAL TRENSMISSION The principal transmitters are: acetylcholine ( AC ) and Noradrenaline (norepinephrine ). I - ACETYLCHOLINE (Cholinergi...

THE AUTONOMIC NERVOUS SYSTEM CHEMICAL TRANSMISSION BY PROF. A. EMAD OMAR ZAKI FALL 2024 CHEMCAL TRANSMISSON  CHEMICAL TRENSMISSION The principal transmitters are: acetylcholine ( AC ) and Noradrenaline (norepinephrine ). I - ACETYLCHOLINE (Cholinergic system) Sites of release : 1 - All preganglionic neurons. 2 - All autonomic ganglia. 3 - All parasympathetic postganglionic neurons. 4 - Sympathetic postganglionic neurons to sweat glands and vasodilators of blood vessels of skeletal muscles. 5 - Adrenal medulla. 6 - Neuromuscular junction. Sites of the cholinergic fibers  Acetyl choline is the Chemical transmitter in the Parasympathetic NS, so it is called the cholinergic system. Synthesis Acetyl choline : Choline + Active acetate choline acetyl transferase Acetylcholine Fate (destruction) of acetyl choline: *Ach is broken down by choline esterase enzyme. Acetic acid Choline esterase enzyme Acetyl choline Choline base *Destruction of the acetyl choline occurs at faster rate compared to the destruction of noradrenaline. II - NORADRINALINE (Adrenergic system) NE is present in granulated vesicles of nerve terminals present in most sympathetic postganglionic endings and some brain neurons. synthesis : hydroxylase Tyrosine DOPA decarboxylase DOPA Dopamine Dopamine enters granulated vesicles to be converted to NE.  Sites of the adrenergic fibers ADRENERGIC FIBERS All postganglionic sympathetic fibers Except: Sweat glands & blood vessels of skeletal muscles  Fate (inactivation) of catecholamine 1-Active neuronal 3-Inactivation by COMT reuptake enzyme (catechol -O- methyl transferase) 2-Inactivation by MAO enzyme (monamine oxidase enzyme)  Autonomic receptors They are chemical structures found mainly on the cell membrane of the effector organs. They are affected by the combination with chemicals or drugs. They are classified into 2 main groups: Cholinergic Adrenergic receptors receptors  Cholinergic receptors It is the division of the autonomic receptors which can be stimulated by acetyl choline. It is classified into 2 types according to its sensitivity to drugs. Muscarinic Nicotinic receptors receptors Stimulated by Stimulated by muscarine Nicotine  Actions Of Acetylcholine (Cholinergic actions ) A - Muscarinic actions (Parasympathetic): 1. Cardiac inhibition and decrease heart rate. 2. Pupillary constriction. Accomodation. 3. Stimulate salivary secretion. 4. Stimulate gastrointestinal secretion and motility 5. Contraction of urinary bladder and rectum. 6. Bronchoconstriction.  Actions Of Acetylcholine (Cholinergic actions ) B - Nicotinic action : 1 - Stimulation of autonomic ganglia. 2 - Stimulate adrenal medulla to secrete adrenaline and nor adrenaline. 3 - Stimulate NM junction causing skeletal muscle contraction.  Adrenergic receptors It is the division of the autonomic receptors which can be stimulated by catecholamine (epinephrine & norepinephrine). It is classified into 2 types according to its sensitivity to drugs. Alpha ( α ) Beta (ß ) receptors receptors  Alpha ( α ) Beta ( ß ) receptors receptors Stimulated Mainly by Mainly by by: noradrenaline adrenaline. Blocked by: Phentolamine Propranolol. Subtype α1 And α2 ß 1 and ß 2 NB: -α1 and ß 1 receptors have excitatory actions. - α 2 and ß 2 receptors have inhibitory actions.  Alpha ( α ) Beta ( ß ) Action receptors receptors mostly On Smooth mostly excitatory. inhibitory. Muscle Cause contraction Cause relaxation On Blood Vasoconstriction vasodilation Vessels Contraction of Relaxation of Sphincters Sphincters (GIT, Sphincters Bladder, and rectum)  Drugs the action of parasympathetic NS They are the drugs that can increase or decrease the action of the parasympathetic Ns. They are classified into: Parasympathomimetic Parasympatholytic drugs drugs  Parasympathomimetic drugs They are drugs which can induce effects similar to the Ach. (or increase its actions). They also called choline agonists. They include: 1-Drugs stimulating the 2-Drugs cholinergic inhibiting the receptors choline esterase enzyme A.Drugs stimulating the cholinergic receptors: Muscarinic agonists Nicotinic agonists Ex. Muscarinic Ex. Nicotine small dose B-Choline esterase inhibitors: Reversible choline esterase inhibitors Irreversible choline Its action is temporary. esterase inhibitors * Its *. action is permanent Ex. Eserine Ex. Parathion Prostigmine  Parasympatholytic drugs They are drugs which can block the effects of Ach (or decrease its actions). They include 1- Muscarinic blockers Ex. Atropine 2-Nicotinic blockers Used as: -Ganglionic blockers *Pupil dilator. Ex. Nicotine large dose *Spasmolytic. Hexamethonium. *Decrease bronchial secretion. -Neuromuscular blockers: Ex. Curare  Drugs that modify the action of sympathetic NS They are the drugs that can increase or decrease the action of the sympathetic Ns. They are classified into: sympathomimetic sympatholytic drugs drugs  Sympathomimetic drugs They are drugs which can induce effects similar to the catecholamine (or increase its actions). They include: 3-Drugs stimulating the adrenergic receptors 1-Drugs stimulating the ganglia -α agonists Ex. Noradrenaline Ex.Nicotine small -ß agonists Ex. Adrenaline dose 2-Drugs increasing the release of NE from nerve endings Ex. Amphetamine  Sympatholytic drugs They are drugs which can block the effects of catecholamine (or decrease its actions). They include: 3-Drugs block the adrenergic receptors -α blockers Ex. Phentolamine 1-Drugs block the - ß blockers Ex. Propranolol ganglia Ex.Nicotine large dose 2-Drugs decreasing the release of NE from nerve endings Ex. Reserpine THANK YOU