Physiology of the Autonomic Nervous system (ANS)

1. Physiology of the Autonomic Nervous system (ANS) • حساس محمد حساس • Dr. Taha Sadig Ahmed و • Mb, BS ( University of Khartoum ). • PhD (University of Bristol , England . • Consultant , Clinical Neurophysiology .

2. A.1. The autonomic nervous system: • is regulated by the Hypothalamus • It regulates activities of : • (1) Visceral muscles : which are involuntary , and include • cardiac muscle , and • smooth moscle in arterioles and the gastro-intesinal tract (GIT) . • (2) Glands ( e.g. , sweat glands and GIT glands ) • It consists of 2 subdivisions: Figure 11-2

3. A.2 The autonomic nervous system pathways: • The autonomic division consists of two efferent neurons in series Tasrget tissue : effector Effector Fig. 11-4

4. Higher control of autonomic function • Sympathetic functions regulated by posterior hypothalamus • Parasympathetic functions regulated by anterior hypothalamus

5. The ANS has 2 subdivisions : sympathetic and parasympathetic

6. Effect of sympathetic stimulation • Sympathetic part of ANS is active during fear, anxiety, sever pain preparing the body for fight or flight • Promoting mechanisms which increase energy & metabolism

7. Effect of parasympathetic stimulation • Parasympathetic system activities is related to relaxed state • Vegetative function: • Feeding • Resting • Part of the sexual function

8. Sympathetic (Thoracolumbar) System 1.The preganglionic fibers are short ( because most ganglia are paravertebral ) and postgang fibers are long. 2. Pregang fibers are myelinated and postgang fibers unmyelinated . 3.Pregang fibers secrete ACh in ganglia 4. The cholinergic receptor in ganglia is nicotinic 5.The neurotransmitter secreted by postgang fibers is Norepinephrine , except in sweat glands and blood vessels in skeletal muscle (in the latter cases it is ACh). 6.There is muchdivergence . The ratio (pre/post) being = 1/10 or more . This divergence implies simultaneous diffuse ( generalized ) actions .

9. Parasympathetic (Craniosacral ) system : 1.The preganglionic neurons are long and postgang fibers are short ( because the parasympathetic ganglia are located either close to the arget organ or embedded in its wall . 2. Pregang fibers are myelinated and postgang fibers unmyelinated . 3.Pregang fibers secrete ACh in ganglia 4. The cholinergic receptor in ganglia is nicotinic 5.The neurotransmitter secreted by postgang fibers is ACh 6. The receptors on the target organ is cholinergic muscarinic ( can be blocked by Atropine ). 7.There is little divergence. The ratio (pre/post) = 1/3. The limited divergence results in more specific and selective actions.

10. Effect of sympathetic & parasympathetic stimulation

11. Other Glands

13. The Heart

15. GIT Digestive and Excretory Functions

16. Genito-urinary Systems

17. Metabolic and Other Functions

18. It should be noted that • Under physiological conditions , nearly all sympathetic and parasympathetic activities are opposite ( contradictory ) to each other ; however , the two systems cooperate (& may act in unison/accord ) in • (1) salivary secretion ( sympathetic  scanty secretion rich in enzymes , parasympathetic  Watery , copious secretion ) , • (2) Emotional stress : parasympathetic  increased tear and nasal secretions , sympathetic  increased heart-rate , BP , etc • (3) Sexual intercourse : parasympathetic  erection of the penis or clitoris , sympathetic  ejaculation or orgasm

19. Autonomic Neurotransmitter • All preg. Fibres (sympathetic and parasympathetic ) secrete acetylcholine at the ganglia . • All postganglionic parasympathetic fibers secrete acetylcholine at target organs . • Most postganglionic sympathetic fibers secrete norepinephrine at target organs . • Postganglionic sympathetic fibers to sweat gland & blood vessels of skeletal muscles release acetylcholine • All epinephrine in the bloodstream comes from the adrenal medulla . Postganglionic sympathetic nerves can not synthesize epinephrine from its precursor which is norepinephrine .

20. Actions of Norepinephrine and Epinephrine Adrenergic( Alpha and Beta ) Receptors • Norepinephrine acts on both alpha and beta receptors , but it acts much better on alpha than beta receptors . • Epinephrine excites both α & β equally .

21. Distribution of Adrenergic Receptors • αis found in : • Iris • Blood vessels , especially arterioles • GIT • β is found in : • Heart • Bronchioles • Skeletal muscle • GIT

22. Noteworthy Effects of Alpha or Beta Receptor Stimulation by Norepinephrine or by Epinephrine

23. Adrenergic Receptor Stimulants • Norepinephrine and Epinephrine • Salbutamol ( Beta 2 stimulant , therefore useful in management of Bronchial Asthma ) .

24. Adrenergic Receptors Blockers • α blockers: • Prazosin (α 1) • Yohimbine (α 2) • β blockers: • Propranolol (β1 & β2) • Atenolol (β 1)

25. Cholinergic receptors , all of them are stimulated by acetylcholine and drugs which mimic it ( simulate its action ) • They are divided into : • Nicotinic ( in all ganglia ) , stimulated by small dose of Nicotine and inhibited by a large dose of Nicotine • Muscarinic ( in target organs ) , and are blocked by Atropine. Therefore , atropine injection is used for relief of colic , and to dry saliva before general anesthesia .

26. Drugs that you should know • Epinephrine ( can be used in Tt of asthma , but disadvantage is … ? ) • Salbutamol ( ventolin ) . • Propranolo ( inderal ) , can be used in Tt of hypertension , but cintra-indicated (C/I) in cases of … ? • Atenolol ( tenormin ) , used for what ? . • Atropine ( used for what ? )

27. END