Autonomic Nervous System-II L15 PDF

‫بسم الله الرحمن الرحيم‬ Autonomic Nervous System-II Dr.Mohammed Sharique Ahmed Quadri Dr. Abdelrahman Mustafa Department of Basic Medical Sciences Division of Physiology Faculty of Medicine Almaarefa University ...

‫بسم الله الرحمن الرحيم‬ Autonomic Nervous System-II Dr.Mohammed Sharique Ahmed Quadri Dr. Abdelrahman Mustafa Department of Basic Medical Sciences Division of Physiology Faculty of Medicine Almaarefa University  Autonomic Neurotransmitters Preganglionic sympathetic as well as parasympathetic are known as cholinergic as they secret acetylcholine. Post ganglionic sympathetic fibers are known as adrenergic as they secret norepinephrine (EXCEPT FIBERS TO SWEAT GLAND) Post ganglionic parasympathetic fibers are known as cholinergic as they secret acetylcholine.  Autonomic Neurotransmitter Receptors Tissues innervated by autonomic nervous system have one or more of several different receptor types for postganglionic chemical messengers – Cholinergic receptors – bind to Ach -2 types Nicotinic receptors – found on postganglionic cell bodies of all autonomic ganglia Muscarinic receptors – found on effector cell membranes – Andrenergic receptors – bind to norepinephrine and epinephrine Alpha (α) receptors Beta (β) receptors  NICOTINIC RECEPTORS (PREGANGLIONIC) ACTIVATED BY ACETYL CHOLINE ENDOGENOUSLY AND NICOTINE EXOGENOUSLY BLOCKED BY CURARE AND HEXAMETHONIUM  MUSCARINIC RECEPTORS (POSTGANGLIONIC) ACTIVATED BY ACETYL CHOLINE ENDOGENOUSLY AND MUSCARINE EXOGENOUSLY BLOCKED BY ATROPINE  Properties of cholinergic receptors Nicotinic receptors: binding of Ach to these receptors initiates opening of non specific cation channels. Muscarinic receptors : binding of Ach initiates G protein linked receptors pathways , depending on effector organ. ADRENERGIC RECEPTORS In general α1 excitatory β1 α2 inhibitory β2  Properties of adrenergic receptors α1 & α2 receptors have greater sensitivity to norepinephrine β2 receptors binds exclusively with epinephrine β1 receptors have equal affinity for epinephrine and norepinephrine All adrenergic receptors are linked to G protein – Activation of β1 & β2 activates cAMP – Activation of α1 activates IP3 /Ca2+ – Activation of α2 inhibits cAMP in target cells Effect of ANS ON VARIOUS ORGANS Effect of ANS ON VARIOUS ORGANS  Effect of ANS ON VARIOUS ORGANS ORGAN S P HEART + - CONSTRICT(MOST DILATE (PENIS BLOOD ORGANS) AND CLITORIS) VESSELS DILATE ( VESSELS IN SKELETAL MUSCLES) BRONCHIOLES DILATE CONSTRICT PUPIL DILATE CONSTRICT DIGESTION INHIBIT ENHANCE  norepinephrine Site of release -Adrenal medulla ( 80% of its -Adrenal medulla ( 20% of its secretion ). secretion ). -Sympathetic postganglionic nerve endings. Action on Acts on both α and β receptors. Acts mainly on α receptors. adrenergic receptors Effect on the More strong Less strong heart Effect on the Vasoconstriction , Vasoconstrictor only. blood vessels but it causes vasodilation in the I.e. it has more potent pressor BVs of the skeletal muscle and action. liver Relaxing effect More strong Less strong on the GIT  Autonomic agonist and antagonist Agonist : Binds to neurotransmitter’s receptor and causes the same response as neurotransmitter would. – E.g. Salbutamol β2 agonist ( bronchodilator) Antagonist : Binds with the receptor preventing the neurotransmitter from binding and causing a response. – E.g. atropine blocks the effect of Ach on muscarinic receptors ( blocks the parasympathetic effect). Use to suppress the salivary and bronchial secretion before surgery – Metaprolol selectively blocks the β1 receptors use for treating blood pressure(β1 in heart )  Regions of CNS Involved in Control of Autonomic Activities Hypothalamus plays important role in integrating autonomic, somatic, and endocrine responses that automatically accompany various emotional and behavioral states Medulla within brain stem is region directly responsible for autonomic output( cardiovascular & respiratory centers) Some autonomic reflexes, such as urination, defecation, and erection, are integrated at spinal cord level  References Human physiology by Lauralee Sherwood, seventh edition Text book physiology by Guyton &Hall,11th edition Text book of physiology by Linda.s contanzo,third edition