1. Lecture 14 & 15 Dr. Zahoor Ali Shaikh 1

2. 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. 2

3. 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 3

4. 4 FUNCTIONAL COMPONENTS OF NERVOUS SYSTEM

5. 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) has two major sub- divisions: 1. Sympathetic Autonomic Nervous System 2. Parasympathetic Autonomic Nervous System We will discuss each one. 6

7. 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 7

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

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10. 1. Origin Sympathetic nerve fiber originate in the spinal cord from lateral horn cell from thoraco lumber region. T 1 - T 12 and L 1 – L 2 /L 3 Therefore, called thoraco lumber outflow. 10

11. 11 SYMPATHETIC ANS

12. 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. 12

13. 13 SYMPATHETIC ANS ORGANIZATION

14. 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. 14

15. 15 SYMPATHETIC ANS

16.  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. 16

17. 3. Chemical Transmitters Chemical transmitter at - preganglionic sympathetic nerve ending is acetylcholine - postganglionic sympathetic nerve ending is nor- epinephrine. Sympathetic fibers which release nor adrenaline (nor epinephrine) are called adrenergic fibers. 17

18. 18 SYMPATHETIC ANS CHEMICAL TRANSMITTERS

19. 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. 19

20. 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). 20

21. 21 sympathetic dominance

22. 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 22

23. - 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 23

24. 24 Structures Innervated by Sympathetic & Parasympathetic ANS

25. 25 Structures Innervated by Sympathetic & Parasympathetic ANS

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28. 5. Receptors Two major types of adrenergic receptors on which nor- epinephrine acts are: - Alpha ( α) – sub divided in α 1 and α 2 - Beta (β) – sub divided in β 1 and β 2 They are present on the cell membrane of the Effector organs. Alpha α 1 are excitatory e.g. blood vessels (vasoconstriction) α 2 are inhibitory e.g. intestine smooth muscle (relaxation) 28

29. Beta adrenergic receptors - β 1 are excitatory – heart (increase Heart Rate) - β 2 inhibitory – lungs, broncho dilation  Remember - Type“1” e.g. α 1, β 1 – excitatory - Type “2” e.g. α 2, β 2 – inhibitory - Preganglionic sympathetic fibers which are cholinergic i.e. secretes acetylcholine (ACH). This activates nicotinic receptors present in the ganglion. 29

30. 30 SYMPATHETIC ANS RECEPTORS

31. 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) 31

32. 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. 32

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36. 1. 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 S 2,3,4. Therefore, called craniosacral outflow. Major nerve of parasympathetic ANS is 10 th cranial nerve (vagus). NOTE (Names of Cranial nerves) III – Oculomotor VII – Facial IX – Glassophyrangeal X – Vagus 36

37. 37 PARASYMPATHETIC ANS

38. 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. 38

39. 39 PARASYMPATHETIC ANS

40. 3. Chemical Transmitters Chemical transmitter at - preganglionic parasympathetic nerve ending is acetylcholine - postganglionic parasympathetic nerve ending is acetylcholine Parasympathetic fibers which release acetylcholine are called Cholinergic fibers. 40

41. 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. 41

42. 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 42

43. 43 parasympathetic dominance

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45. 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. 45

46. 46 PARASYMPATHETIC ANS RECEPTORS

47.  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. 47

48. Blood vessels – most arterioles and veins are innervated by sympathetic ANS, but not by parasympathetic ANS. Sympathetic ANS causes vasoconstriction ( α 1 receptors) in blood vessels, but causes vasodilatation in skeletal muscle blood vessels (β 2 receptors). The only blood vessels which receive both sympathetic and parasympathetic fibers are male and female sex organs. 48

49. 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. 49

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

51. Drugs are available which work as agonist and antagonist at the receptor site. Agonist give effect like neurotransmitter. Antagonist block the receptor, therefore, no effect of neurotransmitters occurs. Example of drugs acting in sympathetic ANS: - β 1 blocker e.g. metoprolol, decreases heart rate - salbutamol (Ventolin) activates β 2 adrenergic receptors and causes broncho dilatation, therefore used in bronchial asthma 51

52. Example of drugs acting in parasympathetic ANS: - atropine blocks the effect of acetylcholine at the muscarinic receptors (postganglionic parasympathetic effect of acetylcholine), therefore atropine decreases salivary and bronchial secretion Ganglionic Blocker - Hexamethonium blocks the nicotinic receptors at autonomic ganglion 52

53. Many regions of central nervous system are involved in control of ANS, they are 1. Prefrontal association cortex – influences emotional expression (mediated through hypothalamus, medullary pathways). 2. Hypothalamus – affects emotions and behavioral state e.g. increase heart rate, blood pressure with anger or fear (via medulla) 53

54. 3. Medulla In brain stem – directly responsible for autonomic output. It has center for control of cardiovascular, respiratory and digestive activity 4. Spinal cord – some autonomic reflexes are integrated at spinal cord level, therefore, called spinal reflexes e.g. urination, defecation, male and female sex organ function. All these spinal reflexes are controlled by higher level of consciousness. 54

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56. 56 SYMPATHETIC ANS 1. Origin 2. Organization 3. Chemical Transmitters 4. Actions 5. Receptors 6. Dominance 7. Drugs acting on adrenergic and muscarinic receptors PARASYMPATHETIC ANS Do the comparison yourself

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