Chapter 13

1. Chapter 13 Physiology of the Peripheral Nervous System

2. Physiology of the Peripheral Nervous System • Divisions of the nervous system • Overview of autonomic nervous system functions • Basic mechanisms by which the autonomic nervous system regulates physiologic processes • Anatomic considerations • Introduction to neurotransmitters of the peripheral nervous system

3. Physiology of the Peripheral Nervous System • Introduction to receptors of the peripheral nervous system • Exploring the concept of receptor subtypes • Locations of receptor subtypes • Functions of cholinergic and adrenergic receptor subtypes • Receptor specificity of adrenergic neurotransmitters • Neurotransmitter life cycles

4. Divisions of the Nervous System • Central nervous system • Brain and spinal cord • Peripheral nervous system • Somatic motor • Autonomic (ANS) • Parasympathetic • Sympathetic

5. Overview of Autonomic Nervous System Functions • Three principal functions • Regulate the heart • Regulate secretory glands (salivary, gastric, sweat, and bronchial) • Regulate smooth muscles (bronchi, blood vessels, urogenital system, and GI tract)

6. Parasympathetic Nervous System • Seven regulatory functions • Slowing the heart rate • Increasing gastric secretions • Emptying the bladder • Emptying the bowel • Focusing the eye for near vision • Constricting the pupil • Contracting bronchial smooth muscle

7. Parasympathetic Nervous System • Parasympathetic nervous system (PNS) drugs • Digestion of food • Excretion of waste • Control of vision • Conservation of energy

8. Sympathetic Nervous System Functions • Three main functions • Regulation of cardiovascular system • Maintaining blood flow to the brain • Redistributing blood • Compensating for loss of blood

9. Sympathetic Nervous System Functions • Three main functions (cont’d): 2. Regulation of body temperature • Regulates blood flow to the skin • Promotes secretion of sweat • Induces piloerection (erection of hair)

10. Sympathetic Nervous System Functions • Three main functions (cont’d): 3. Implementation of “fight-or-flight” reaction • Increasing heart rate and blood pressure • Shunting blood away from the skin and viscera • Dilating the bronchi • Dilating the pupils • Mobilizing stored energy

11. Homeostatic Objectives of SNS • Maintenance of blood flow to the brain • Redistribution of blood flow during exercise • Compensation for loss of blood, primarily by causing vasoconstriction SNS = sympathetic nervous system.

12. SNS Body Temperature Regulation • Regulates blood flow to the skin • Dilating surface vessels: accelerates heat loss • Constricting cutaneous vessels: conserves heat • Promotes secretion of sweat glands: helps the body cool • Induces piloerection: promotes heat conservation

13. Fight-or-Flight Response • Increasing heart rate and blood pressure • Shunting blood away from the skin/viscera and into skeletal muscle • Dilating the bronchi to improve oxygenation • Dilating the pupils • Mobilizing stored energy, thereby providing glucose for the brain and fatty acids for the muscles

14. Sympathomimetic Drugs • Primarily used for effects on the • Heart and blood vessels • Hypertension, heart failure, angina pectoris • Lungs • Primarily asthma

15. Basic Mechanisms by Which ANS Regulates Physiologic Processes • Patterns of innervation and control • Feedback regulation • Autonomic tone ANS = autonomic nervous system.

16. Basic Mechanisms by Which ANS Regulates Physiologic Processes • Patterns of innervation and control • Dual innervation opposed: heart rate • Dual innervation complementary: erection and ejaculation • Only one division: blood vessels

17. Fig. 13-1. Opposing effects of parasympathetic and sympathetic nerves.

18. Basic Mechanisms by Which ANS Regulates Physiologic Processes • Feedback regulation • Baroreceptor reflex and blood pressure • Feedback loop • Sensor, effector neurons

19. Fig. 13-2. Feedback loop of the autonomic nervous system.

20. Basic Mechanisms by Which ANS Regulates Physiologic Processes • Autonomic tone • Only one division provides basal control to organ. • Most organs: predominant tone is PNS • Vascular system: predominant tone is SNS

21. Anatomic Considerations • Parasympathetic nervous system • Sympathetic nervous system • Somatic motor system

22. Fig.13-3. The basic anatomy of the parasympathetic and sympathetic nervous systems and the somatic motor system.

23. Sympathetic Nervous System • Neurons • Preganglionic neurons • Postganglionic neurons • Medulla of the adrenal gland • Functional equivalent of the postganglionic SNS neuron

24. Sympathetic Nervous System • Two general sites of action • Synapses: preganglionic/postganglionic • Junction: postganglionic neurons/effector organs

25. Neurotransmitters of the Peripheral Nervous System

26. Fig.13-4. Transmitters employed at specific junctions of the peripheral nervous system.

27. Receptors of the Peripheral Nervous System

28. Receptors of the Peripheral Nervous System

29. Fig. 13-5. Drug structure and receptor selectivity.

30. Exploring the Concept of Receptor Subtypes • What do we mean by the term receptor subtype? • How do we know that receptor subtypes exist? • How can drugs be more selective than natural neurotransmitters at receptor subtypes? • Why do receptor subtypes exist? • Do receptor subtypes matter to us? You bet!

31. Locations of Receptor Subtypes • Knowledge of the sites at which specific receptor subtypes are located will help predict which organs a drug will affect.

32. Classification of Cholinergic and Adrenergic Receptors

33. Functions of Cholinergic and Adrenergic Receptor Subtypes • Functions of cholinergic receptor subtypes • Activation of nicotinicN (neuronal) receptors • Activation of nicotinicM (muscle) receptors • Activation of muscarinic receptors

34. Fig. 13-6. Locations of cholinergic and adrenergic receptor subtypes.

35. Functions of AdrenergicReceptor Subtypes • Alpha1 • Vasoconstriction • Ejaculation • Contraction of bladder neck and prostate • Alpha2 • Located in presynaptic junction • Minimal clinical significance

36. Functions of AdrenergicReceptor Subtypes • Beta1 • Heart • Increases • Heart rate • Force of contraction • Velocity of conduction in atrioventricular (AV) node • Kidney • Renin release

37. Functions of AdrenergicReceptor Subtypes • Beta2 • Bronchial dilation • Relaxation of uterine muscle • Vasodilation • Glycogenolysis • Dopamine • Dilates renal blood vessels

38. Receptor Specificity of the Adrenergic Neurotransmitters • Epinephrine can activate all alpha and beta receptors, but not dopamine receptors. • Norepinephrine can activate alpha1, apha2, and beta1 receptors, but not beta2 or dopamine receptors. • Dopamine can activate alpha1, beta1, and dopamine receptors. Note: Dopamine is the only neurotransmitter capable of activating dopamine receptors.

39. Neurotransmitter Life Cycles • Many drugs produce their effects by interfering with specific life cycles. • Life cycle of acetylcholine • Life cycle of norepinephrine • Life cycle of epinephrine

40. 3 Fig. 13-7. Life cycle of acetylcholine. Note that transmission is terminated by enzymatic degradation of ACh and not by uptake of intact ACh back into the nerve terminal. (Acetyl CoA = acetylcoenzyme A, ACh = acetylcholine, AChE = acetylcholinesterase.)

41. Fig. 13-8. Life cycle of norepinephrine. Note that transmission is terminated by reuptake of NE into the nerve terminal and not by enzymatic degradation. Note also the structural similarity between epinephrine and norepinephrine. (DA = dopamine, MAO = monoamine oxidase, NE = norepinephrine.)