AUTONOMIC NERVOUS SYSTEM (ANS)

1. AUTONOMIC NERVOUS SYSTEM (ANS) Lecture 14 & 15 Dr. Zahoor Ali Shaikh

2. NERVOUS SYSTEM GENERAL INTRODUCTION • Central Nervous System (CNS) – brain and spinal cord. • Peripheral Nervous System (PNS) – afferent and efferent branch. PNS • Afferent branch takes message to CNS. • Efferent branch brings message from CNS to Effector organ.

3. NERVOUS SYSTEM GENERAL INTRODUCTION • Skeletal muscle is innervated by efferent division of PNS, but it is voluntary – somatic nervous system. • Autonomic Nervous System (ANS) is the part of efferent division of PNS, but it is involuntary. • We will discuss ANS

4. FUNCTIONAL COMPONENTS OF NERVOUS SYSTEM

5. ANS • Autonomic nerve pathway • Extends from CNS to an innervated organ • Two-neuron chain • Preganglionic fibers arise from CNS – they synapses with cell body (ganglion) of second neuron • Postganglionic fiber arise from ganglia and innervates Effector organ

6. AUTONOMIC NERVOUS SYSTEM(ANS) • Autonomic Nervous System (ANS) has two major sub- divisions: • Sympathetic Autonomic Nervous System • Parasympathetic Autonomic Nervous System We will discuss each one.

7. AUTONOMIC NERVOUS SYSTEM (ANS) • We will discuss Sympathetic and Parasympathetic ANS under following headings: 1. Origin 2. Organization 3. Chemical Transmitters 4. Actions 5. Receptors 6. Exceptions in ANS 7. Comparison between Sympathetic & Parasympathetic ANS

8. AUTONOMIC NERVOUS SYSTEM (ANS) • ANS supplies cardiac muscle, smooth muscle, blood vessel, GIT, salivary glands, sweat glands, most exocrine glands and some endocrine glands, adipose tissue (fat).

9. SYMPATHETIC AUTONOMIC NERVOUS SYSTEM

10. SYMPATHETIC AUTONOMIC NERVOUS SYSTEM • Origin • Sympathetic nerve fiber originate in the spinal cord from lateral horn cell from thoraco lumber region. • T1 - T12 and L1 – L2/L3 • Therefore, called thoraco lumber outflow.

11. SYMPATHETIC ANS

12. SYMPATHETIC AUTONOMIC NERVOUS SYSTEM 2. Organization • Sympathetic ANS is Two - neuron system. • The cell body of first neuron is located in the CNS (spinal cord at lateral horn cell).Its axon, the preganglionic fiber makes the synapse with the cell body of second neuron which lies within sympathetic chain ganglion (collection of neuronal cell bodies). • The axon of the second neuron, the post ganglionic fiber arises from the ganglion and innervates the Effector organ.

13. SYMPATHETIC ANS ORGANIZATION

14. SYMPATHETIC AUTONOMIC NERVOUS SYSTEM • In Sympathetic ANS - Preganglionic fibers are short and post ganglionic fibers are long. - Preganglionic fibers synapse with sympathetic ganglion chain also called Sympathetic trunk which is located on either sides of spinal cord. - Post ganglionic fibers are large and originate in the ganglion chain and go to the Effector organ.

15. SYMPATHETIC ANS

16. SYMPATHETIC AUTONOMIC NERVOUS SYSTEM • NOTE • Some preganglionic fiber pass through the ganglion chain without synapsing. • Instead they synapse with sympathetic collateral ganglion and post ganglionic fiber arises from collateral ganglion and innervates the Effector organ.

17. SYMPATHETIC AUTONOMIC NERVOUS SYSTEM 3. Chemical Transmitters • Chemical transmitter at - preganglionicsympathetic nerve ending isacetylcholine - postganglionic sympathetic nerve ending is nor-epinephrine. • Sympathetic fibers which release nor adrenaline (nor epinephrine) are called adrenergic fibers.

18. SYMPATHETIC ANS CHEMICAL TRANSMITTERS

19. SYMPATHETIC AUTONOMIC NERVOUS SYSTEM 4. Actions • Sympathetic and Parasympathetic ANS, generally have opposite effects in a particular organ. Important • Instead of memorizing, it is better to see the actions of Sympathetic ANS by understanding the circumstances under which it dominates.

20. SYMPATHETIC AUTONOMIC NERVOUS SYSTEM Time of sympathetic dominance • Sympathetic ANS dominates in the stressful situation e.g. fighting, frightened, examinations. • Therefore, sympathetic response is called fight or flight response (makes body ready to fight or run away from the threat).

21. sympathetic dominance

22. SYMPATHETIC AUTONOMIC NERVOUS SYSTEM - ACTIONS • When there is more sympathetic activity, there is - increased heart rate, increased force of contraction of heart - increased blood pressure (due to vasoconstriction) - respiratory airways are open (broncho dilation to increase air flow) - Pupils dilate

23. SYMPATHETIC AUTONOMIC NERVOUS SYSTEM (cont) - Sweating is increased • Glycogen and fat stores are broken down • Blood vessel to skeletal muscle are dilated to increase blood flow in anticipation of increased physical activity • Digestive and urinary activities are inhabited at the time of threat by sympathetic ANS

24. Structures Innervated by Sympathetic & Parasympathetic ANS

25. Structures Innervated by Sympathetic & Parasympathetic ANS

28. SYMPATHETIC AUTONOMIC NERVOUS SYSTEM 5. Receptors • Two major types of adrenergic receptors on which nor-epinephrine acts are: - Alpha (α) – sub divided in α1 and α2 - Beta (β) – sub divided in β1 and β2 • They are present on the cell membrane of the Effector organs. Alpha • α1 are excitatory e.g. blood vessels (vasoconstriction) • α2 are inhibitory e.g. intestine smooth muscle (relaxation)

29. SYMPATHETIC AUTONOMIC NERVOUS SYSTEM • Beta adrenergic receptors - β1 are excitatory – heart (increase Heart Rate) - β2 inhibitory – lungs, broncho dilation • Remember • Type“1” e.g. α1, β1 – excitatory • Type “2” e.g. α2, β2 – inhibitory • Preganglionic sympathetic fibers which are cholinergic i.e. secretes acetylcholine (ACH). This activates nicotinic receptors present in the ganglion.

30. SYMPATHETIC ANS RECEPTORS

31. ADRENAL MEDULLA • It is modified part of sympathetic ANS. • There are two adrenal glands, each lying above the kidney. They are endocrine glands. • Adrenal glands has two parts - Adrenal cortex (outer portion) - Adrenal medulla (inner portion)

32. ADRENAL MEDULLA • It is modified sympathetic ganglion. • It does not give postganglionic fibers, but secretes epinephrine and nor-epinephrine directly into the blood, therefore, it is called Endocrine gland. • Adrenal medulla secretes - 80% Epinephrine - 20% Norepinephrine • These hormones increase the activity of sympathetic ANS.

35. PARASYMPATHETIC AUTONOMIC NERVOUS SYSTEM

36. PARASYMPATHETIC AUTONOMIC NERVOUS SYSTEM • Origin • Parasympathetic ANS – preganglionic fibers originates from the nuclei of cranial nerves III, VII, IX, X (midbrain, pons and medulla) and spinal cord sacral segments S2,3,4. • Therefore, called craniosacral outflow. • Major nerve of parasympathetic ANS is 10th cranial nerve (vagus). NOTE (Names of Cranial nerves) III – Oculomotor VII – Facial IX – Glassophyrangeal X – Vagus

37. PARASYMPATHETIC ANS

38. PARASYMPATHETIC AUTONOMIC NERVOUS SYSTEM 2. Organization • Parasympathetic ANS is Two - neuron system. • Preganglionic fibers are longer • Postganglionic fibers are shorter • Preganglionic fibers end on the ganglia that lies in or near the Effector organ. • Postganglionic fibers are very short that they end on the Effector organ.

39. PARASYMPATHETIC ANS

40. PARASYMPATHETIC ANS 3. Chemical Transmitters • Chemical transmitter at - preganglionicparasympathetic nerve ending isacetylcholine - postganglionic parasympathetic nerve ending is acetylcholine • Parasympathetic fibers which release acetylcholine are called Cholinergic fibers.

41. PARASYMPATHETIC AUTONOMIC NERVOUS SYSTEM 4. Actions • Sympathetic and Parasympathetic ANS, generally have opposite effects in a particular organ. Important • Instead of memorizing, it is better to see the actions of Parasympathetic ANS by understanding the circumstances under which it dominates.

42. PARASYMPATHETIC AUTONOMIC NERVOUS SYSTEM Time of parasympathetic dominance • Parasympathetic ANS dominates at the time of relaxation, digestion, rest and sleep. • At the time of rest and digestion Heart - heart rate decreases, force of contraction of heart decreases GIT – increases digestion, gut motility, secretions and promotes defecation. - promotes diuresis

43. parasympathetic dominance

45. PARASYMPATHETIC ANS 5. Receptors • There are two types - Nicotinic receptors – are present in autonomic ganglion. Preganglionic parasympathetic fibers which secrete acetylcholine act on nicotinic receptors. - Muscarinic receptors – are found in target organs that is the cell membrane of cardiac muscle, smooth muscle, glands. Post ganglionic parasympathetic fibers which are cholinergic i.e. secrete acetylcholine act on muscarinic receptors.

46. PARASYMPATHETIC ANS RECEPTORS

47. ADVANTAGE OF DUAL (symp & parasymp) AUTONOMIC INNERVATION • What is the advantage of dual ANS supply, whose actions oppose each other? • It is like accelerator and brake of car, to have precise control of activity of the organ.

48. Exceptions in ANS • Blood vessels – most arterioles and veins are innervated by sympathetic ANS, but not by parasympathetic ANS. • Sympathetic ANS causes vasoconstriction (α1 receptors) in blood vessels, but causes vasodilatation in skeletal muscle blood vessels (β2 receptors). • The only blood vessels which receive both sympathetic and parasympathetic fibers are male and female sex organs.

49. Exceptions in ANS (cont) • Salivary Glands are supplied by both sympathetic and parasympathetic ANS but both stimulate salivary secretion. Parasympathetic – causes increased amount of watery secretion. Sympathetic causes little increase of thick saliva secretion.

50. Exceptions in ANS (cont) • Sweat glands – are supplied by sympathetic ANS only and chemical transmitter at postganglionic sympathetic nerve ending is acetylcholine (NOT Norepinephrine).