Autonomic Nervous System-II بسم الله الرحمن الرحيم Autonomic Nervous System-II Dr.Mohammed Sharique Ahmed Quadri Assistant prof. Physiology Al Maarefa College

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 & blood vessels of skeletal muscle, they are cholinergic) 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.

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

In general α1 excitatory β1 α2 inhibitory β2

Adrenaline/epinephrine Noradrenaline/norepinephrine Site of release -Adrenal medulla ( 80% of its secretion ). -Adrenal medulla ( 20% of its secretion ). -Sympathetic postganglionic nerve endings. Action on adrenergic receptors Acts on both α and β receptors. Acts mainly on α receptors. Effect on the heart More strong Less strong Effect on the blood vessels Vasoconstriction , but it causes vasodilation in the BVs of the skeletal muscle and liver Vasoconstrictor only. I.e. it has more potent pressor action. Relaxing effect on the GIT

Effect of ANS ON VARIOUS ORGANS

EFFECTS OF ANS

Functions of the sympathetic NS sympathetic NS is characterized by: It discharges during emergency and stress ( fight and flight reaction). It acts as one unit (generalized action). It has catabolic action. Delays evacuation of visceral content.

Functions of the parasympathetic NS Parasympathetic NS is characterized by: It discharges during rest and sleep. Its action is localized. It has anabolic action (conserve body stores ). It increases gastrointestinal secretion & motility i.e. secretomotor.

Structures supplied only by sympathetic nervous system: Skin Sweat glands (sympathetic cholinergic) Piloerector muscle. Blood vessels all over the body except the penis & clitoris . Dilator papillae muscle. Blood vessels of the skeletal muscles Adrenal medulla. Capsule of the spleen .

Structures supplied only by Parasympathetic nervous system: Constrictor papillae muscle.

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

Regulation of autonomic nervous system

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