1. PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 14 The Autonomic Nervous System

2. Copyright © 2010 Pearson Education, Inc. Autonomic Nervous System (ANS) The ANS consists of motor neurons that: Innervate smooth and cardiac muscle and glands Make adjustments to ensure optimal support for body activities Operate via subconscious control

3. Copyright © 2010 Pearson Education, Inc. ANS Versus Somatic Nervous System (SNS) The ANS differs from the SNS in the following three areas 1. Effectors The effectors of the SNS are skeletal muscles The effectors of the ANS are cardiac muscle, smooth muscle, and glands

4. Copyright © 2010 Pearson Education, Inc. ANS Versus Somatic Nervous System (SNS) 2. Efferent pathways In the SNS heavily myelinated axons of the somatic motor neurons extend from the CNS to the effector (one neuron) Efferent pathways in the ANS are a two-neuron chain The preganglionic (first) neuron has a lightly myelinated axon The post-ganglionic (second) neuron extends to an effector organ Pre-ganglionic Ganglion Post-ganglionic

5. Copyright © 2010 Pearson Education, Inc. 3. Target organ responses All somatic motor neurons release Acetylcholine (ACh), which has an excitatory effect In the ANS: Preganglionic fibers release ACh Postganglionic fibers release norepinephrine or ACh and the effect is either stimulatory or inhibitory ANS effect on the target organ is dependent upon the neurotransmitter released and the receptor type of the effector ANS Versus Somatic Nervous System (SNS)

6. Copyright © 2010 Pearson Education, Inc. Autonomic Nervous SystemSomatic Nervous SystemCharacteristic Smooth muscle, Cardiac Muscle, Glands Voluntary (skeletal) muscleEffectors Adjustment within the internal environment (homeostasis) Adjustment to external environment. General function 21 Number of neurons from CNS to effectors Chain ganglia, collateral ganglia or terminal ganglia 0 Ganglia outside the CNS Acetylcholine, adrenaline, noradrenalin AcetylcholineNeurotransmitter On NMJ - nicotinic receptors – ACh always excitatory

7. Copyright © 2010 Pearson Education, Inc. http://www.sirinet.net/~jgjohnso/nervous.html Enteric nervous system Divisions of the ANS

8. Copyright © 2010 Pearson Education, Inc. Divisions of the ANS 1.Sympathetic division 2.Parasympathetic division Dual innervation Almost all visceral organs are served by both divisions, but they cause opposite effects

9. Copyright © 2010 Pearson Education, Inc. Division Origin of Fibers Length of Fibers Location of Ganglia SympatheticThoraco - lumbar region of the spinal cord Short pre - ganglionic and long post - ganglionic Close to the spinal cord ParasympatheticBrain and sacral spinal cord Long preganglionic and short postganglioni c In the visceral effector organs Anatomy of ANS

10. Copyright © 2010 Pearson Education, Inc. ANS receptors ANS receptors are divided into 2 groups: Cholinergic – receive and respond to acetylcholine (ACh): Two subgroups that are names of chemicals that mimic some of the actions of Ach: Muscarinic (chemical found in the mushroom Amanita muscarina) Nicotinic (chemical found in the tobacco plant – nicotina tabacum) Adrenergic – receive and respond to norepinephrin (NE) / epinephrine (E) Divided into alpha and beta

11. Copyright © 2010 Pearson Education, Inc. Role of the Parasympathetic Division Concerned with keeping body energy use low Involves the D activities – digestion, defecation, and diuresis Its activity is illustrated in a person who relaxes after a meal Blood pressure, heart rate, and respiratory rates are low Gastrointestinal tract activity is high The skin is warm and the pupils are constricted

12. Copyright © 2010 Pearson Education, Inc. Cranial OutflowCranial NerveGanglionEffector Organ(s) Occulomotor (III)CiliaryEye Facial (VII)Pterygopalatin Submandibular Salivary, nasal, and lacrimal glands Glossopharyngeal (IX) OticParotid salivary glands Vagus (X)Located within the walls of target organs Heart, lungs, and most visceral organs Sacral OutflowS 2 -S 4 Located within the walls of the target organs Large intestine, urinary bladder, ureters, and reproductive organs Parasympathetic Division Outflow

13. Copyright © 2010 Pearson Education, Inc. Nicotinic Receptors Found on Motor end plates of skeletal muscle cells All ganglionic neurons (sympathetic and parasympathetic) Hormone-producing cells of the adrenal medulla Effect of ACh at nicotinic receptors is always direct and stimulatory

14. Copyright © 2010 Pearson Education, Inc. Direct effect – receptors are part of the ion channel Nicotinic receptors

15. Copyright © 2010 Pearson Education, Inc. Muscarinic Receptors Found on All effector cells stimulated by postganglionic cholinergic fibers The effect of ACh at muscarinic receptors Can be either inhibitory or excitatory Depends on the receptor type of the target organ

16. Copyright © 2010 Pearson Education, Inc. Indirect effect – through G-protein and 2 nd messenger Muscarinic (cholinergic) and all adrenergic receptors

17. Copyright © 2010 Pearson Education, Inc. Copyright © The McGraw-Hill Companies, Inc (nACh) (mACh) Parasympathetic pre and post-ganglionic receptors

18. Copyright © 2010 Pearson Education, Inc. ACh (cholinergic) receptors Nicotinic receptors (nACh) Pre-ganglionic Muscarinic receptors (mACh) Post-ganglionic Direct mechanism – open Na+ channels (depolarization) Fast excitatory effect Indirect mechanism – use of G-protein and 2 nd messenger system Slow excitatory M1, M3, M5 Slow inhibitory M2, M4 Inhibition of adenylate cyclase Increase intracellular Ca 2+ release

19. Copyright © 2010 Pearson Education, Inc. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/PNS.html Cholinergic receptors function

20. Copyright © 2010 Pearson Education, Inc. Drugs affecting the parasympathetic nervous system Nicotinic receptors: Agonists at muscles will cause contraction Antagonists at muscles will cause paralysis. Muscarinic receptors: Agonists will cause increased bowel and bladder function, decreased HR, bronchoconstriction, and miosis. Agonists also help in cognition and memory. Antagonists will cause constipation, urinary retention, increased heart rate, bronchodilation, and dilated pupils

21. Copyright © 2010 Pearson Education, Inc. Break down of ACh The effect of ACh is short-lived Inactivated in the synapse by the enzyme acetylcholinesterase (AChE) Inactivated in the surrounding tissues cholinesterase The effect of the parasympathetic division is localized and lasts about 20 msec.

22. Copyright © 2010 Pearson Education, Inc. Role of the Sympathetic Division The sympathetic division is the “fight-or-flight” system Involves E activities – exercise, excitement, emergency, and embarrassment Promotes adjustments during exercise – blood flow to organs is reduced, flow to muscles is increased Its activity is illustrated by a person who is threatened Heart rate increases, and breathing is rapid and deep The skin is cold and sweaty, and the pupils dilate

23. Copyright © 2010 Pearson Education, Inc. Sympathetic Outflow Sympathetic nerves originate inside the vertebral column toward the middle of the spinal cord in the lateral gray horn Arises from spinal cord segments T 1 through L 2 (thoracolumbar outflow). Axons of these nerves leave the spinal cord in the ventral rami of the spinal nerves, and then separate out as 'white rami' The white rami connect to the chain ganglia (paravertebral) extending alongside the vertebral column on the left and right. There are 23 ganglia – 3 cervical, 11 thoracic, 4 lumbar, 4 sacral, and 1 coccygeal The chain ganglia are interconnected by preganglionic fibers All preganglionic fibers go through the chain ganglia.

24. Copyright © 2010 Pearson Education, Inc. Sympathetic Trunks and Pathways Figure 14.6 A preganglionic fiber follows one of three pathways upon entering the paravertebral ganglia 1. Synapse with the ganglionic neuron within the same ganglion 2. Ascend or descend the sympathetic chain to synapse in another chain ganglion 3. Pass through the chain ganglion and emerge without synapsing

25. Copyright © 2010 Pearson Education, Inc. http://www.wisc-online.com/objects/index_tj.asp?objID=AP2704

26. Copyright © 2010 Pearson Education, Inc. Pathways with Synapses in the Adrenal Medulla Some preganglionic fibers pass directly to the adrenal medulla without synapsing Upon stimulation, medullary cells secrete norepinephrine and epinephrine into the blood

27. Copyright © 2010 Pearson Education, Inc. Visceral Reflexes Visceral reflex arcs have the same components as somatic reflexes Main difference: visceral reflex arc has two neurons in the motor pathway

28. Copyright © 2010 Pearson Education, Inc. Referred Pain Visceral pain afferents travel along the same pathway as somatic pain fibers Pain stimuli arising in the viscera are perceived as somatic in origin

29. Copyright © 2010 Pearson Education, Inc. Copyright © The McGraw-Hill Companies, Inc (nACh)   Sympathetic pre and post-ganglionic receptors

30. Copyright © 2010 Pearson Education, Inc. Adrenergic Receptors Two types Alpha (  ) (subtypes  1,  2) Beta (  ) (subtypes  1,  2,  3) Effects of NE depend on which subclass of receptor predominates on the target organ

31. Copyright © 2010 Pearson Education, Inc. NE (adrenergic) receptors - all indirect through G-protein 11 11 Slow excitation 2 nd messenger – cAMP Inhibition or activation of adenylate cyclase slow excitation Slow inhibition 22 22 33 Inhibition of adenylate cyclase Lypolysis (excitation) Increase intracellular Ca 2+ release Slow inhibition

32. Copyright © 2010 Pearson Education, Inc. Drugs affecting the sympathetic nervous system Alpha 1 receptors – agonists will raise BP, antagonists will lower BP Beta 1 receptors – agonists will increase heart rate and strength of contraction, antagonists will decrease heart rate and BP Beta 2 receptors – agonists will increase respiratory airflow, will increase blood flow to skeletal muscles (via blood vessels dilation) antagonists will constrict respiratory flow

33. Copyright © 2010 Pearson Education, Inc. Interactions of the Autonomic Divisions Most visceral organs have dual innervation Dynamic antagonism allows for precise control of visceral activity Sympathetic division increases heart and respiratory rates, and inhibits digestion and elimination Parasympathetic division decreases heart and respiratory rates, and allows for digestion and the discarding of wastes

34. Copyright © 2010 Pearson Education, Inc. Sympathetic Tone Sympathetic division controls blood pressure, even at rest Sympathetic tone (vasomotor tone) Keeps the blood vessels in a continual state of partial constriction

35. Copyright © 2010 Pearson Education, Inc. Parasympathetic Tone Parasympathetic division normally dominates the heart and smooth muscle of digestive and urinary tract organs Slows the heart Dictates normal activity levels of the digestive and urinary tracts The sympathetic division can override these effects during times of stress

36. Copyright © 2010 Pearson Education, Inc. Unique Roles of the Sympathetic Division only sympathetic fibers are found on: The adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels The sympathetic division controls Thermoregulatory responses to heat Release of renin from the kidneys Metabolic effects Increases metabolic rates of cells Raises blood glucose levels Mobilizes fats for use as fuels