Learning Objectives: Describe the anatomical differences between

1. Learning Objectives: Describe the anatomical differences between the sympathetic and parasympathetic nervous systems Describe the differences in the neurotransmitters and their receptors between the two systems Describe how the sympathetic and parasympathetic systems differ in their regulation of the major organ systems Understand the nature of sympathetic and parasympathetic tone

2. Autonomic Nervous System (Involuntary or Visceral Nervous System) I. Function --Overview II. Anatomy III. Neurotransmitters and receptors IV. Specific Organ Effects

3. I. Function-- Overview • Autonomic nervous system controls • involuntary functions: • arterial pressure • gastrointestinal motility • gastrointestinal secretion • urinary bladder emptying • sweating • body temperature • pupilary dilation and constriction Striking feature of the ANS is the rapidity and intensity with which it can change visceral functions (3-5 seconds)

4. nervous system Peripheral nervous system Central nervous system Autonomic nervous system Somatic nervous system Parasympathetic nervous system Sympathetic nervous system

5. Peripheral nervous system Autonomic nervous system Somatic nervous system Innervates heart, blood vessels, visceral organs, glands, and virtually all other organs with smooth muscle; regulates function of these organs in a manner beyond conscious (involuntary or automatic) control Nerves innervating the skeletal muscles; activity is under conscious (voluntary) control

6. Autonomic nervous system Parasympathetic nervous system Sympathetic nervous system “Fight or flight” “rest and digest”

7. ANATOMY ANS is activated by centers located in spinal cord brain stem and hypothalamus ANS often operates by visceral reflexes: subconscious sensory signals from visceral organs can enter the spinal cord, brainstem or hypothalamus and then return subconscious reflex responses directly back to the visceral organ to control its activities

8. ANATOMY Autonomic nerves are composed of two neuron relays. Preganglionic neurons have their cell bodies in the spinal cord and their activity is controlled by higher brain centers and spinal reflexes. Postganglionic neurons send their axons directly to the effector organ. Spinal cord ganglia Preganglionic neuron Postganglionic neuron organ

10. Sympathetic Nervous System 1) preganglionic nerves leave spinal cord at the thoracic and lumbar levels 2) preganglionic axons are short and myelinated 3) postganglionic axons are long and unmyelinated 4) ganglia are located near the spinal cord

11. Sympathetic nervous system.

12. Parasympathetic Nervous System • 1) Nerves leave spinal cord at cranial and sacral levels • cranial nerves innervate head, neck, thorax, • and abdomen • sacral division forms the pelvic nerve and innervates the • remainder of the intestines, bladder and • reproductive organs • 2) Preganglionic axons are myelinated and extremely long • 3) Postganglionic axons are unmyelinated and short • 4) Postsynaptic ganglia located near the effector organ

13. Parasympathetic nervous system cranial sacral

14. Next…………... Neurotransmitters and receptors

15. ALL PREGANGLIONC AXONS USE ACETYLCHOLINE AS THEIR NEUROTRANSMITTER BUT……………. Parasympathetic Postganglionic axons release acetylcholine Sympathetic Postganglionic axons release norepinephrine accept axons on sweat glands, piloerector muscles of the hairs, and some blood vessels which release acetylcholine

16. Adrenal medulla Stimulation of sympathetic innervation of adrenal medulla causes release of large quantities of epinephrine (80%) and norepinephrine (20%)

18. Cholinergic receptors Nicotinic Muscarinic Ganglionic Skeletal muscle Neuronal CNS M1 M3 M5 M2 M4 Adrenergic receptors a1 a2 b a1A a1B a1D a2A a2B a2C b1 b2 b3

19. Receptors in the parasympathetic system Nicotinic receptor Muscarinic receptor Neuroscience, Sinauer Asssoc., Inc

20. Adrenergic receptors in the sympathetic system a2 a1 Neuroscience, Sinauer Asssoc., Inc

21. List of relevant receptors and their messengers Cholinergic receptors: nicotinic receptor--- ligand-gated ion channel muscarinic receptor--- G-protein coupled receptor Adrenergic receptors: alpha (a1 and a2) receptors a1: Gq increase in PI turnover a2: Gi inhibition of adenylate cyclase beta (b1 and b2) receptors b1 b2: Gs stimulation of adenylate cyclase

22. Adrenergic receptors: alpha (a1 and a2) receptors a1: Gq increase in PI turnover a2: Gi inhibition of adenylate cyclase beta (b1 and b2) receptors b1 b2: Gs stimulation of adenylate cyclase • NE and Epi have same potency at a1 receptors • receptors are much more sensitive to catecholamines than a1 receptors NE and Epi are equipotent at b1 receptors b2 receptors are preferentially activated by Epi

23. a1 receptors: vascular smooth muscle, on GI and bladder sphincters, and radial muscle of the eye cause excitation (contraction) Gq IP3 a2 receptors presynaptic nerve terminals, platelets, fat cells, walls of GI tract cause inhibition (relation, dilitation) inhibition of adenlyate cyclase and decrease in cAMP b1 receptors SA node, AV node, ventricular muscle of heart produce excitation (increaes heart rate, contactility, increased conduction velocity stimulation of adenylate cyclase and increase in cAMP b2 receptors vascular smooth muscle of skeletal muscle, bronchioles, walls fo Gi tract and bladder produce relaxation (dilation of vascular smooth muscle and bronchioles, relaxation of bladder wall) stimulation of adenylate cyclase and increase in cAMP

25. Comparison of the Components of the Peripheral Nervous System Parasympathetic Nervous System Preganglionic Postganglionic Neuron Neuron Sympathetic Nervous System Synaptic connection Ganglion near organ At organ Neuron length Long Short Acetylcholine Neurotransmitter Acetylcholine Ganglion near spinal cord At organ Short Long Preganglionic Postganglionic Acetylcholine Norepinephrine Neuron Neuron Somatic Motor NervousSystem Synaptic connection Neuron length At skeletal muscle Neurotransmitter Long Acetylcholine Synaptic connection Neuron length Neurotransmitter

26. Organs are usually innervated by both systems in opposing roles

28. Sympathetic Nervous System Receptors at Target Organs Organ Action Receptor Heart heart rate b1 contactility AV node conduction Vascular smooth constrict blood vessels a1 muscle dilates blood vessels in skeletal muscles Gastrointestinal motility a2, b2 Tract constricts sphincters Bronchioles dilates bronchiolar b2 pupil dilation a1 smooth muscle Bladder relaxes bladder wall b2 constricts sphincter a

29. Sympathetic Nervous Con’t organ action receptor sweat glands sweating muscarinic goose bumps contracts a kidney renin secretion b1 Male genitalia ejaculation a fat cells lipolysis b1

30. Parasympathetic Action Organ Action Receptor Heart heart rate M contractility AV node conduction Gastrointestinal motility M Tract relaxes sphincters Bronchioles constricts M Male sex organs erection M Bladder contracts wall M relaxes sphincter Pupil constriction M

31. Ganglionic blockers These drugs block both divisions of the autonomic nervous system equally. However, the end-organ response may show a predominant adrenergic or cholinergic. Therefore interruption of ganglionic transmission has the effect of selectively eliminating the dominant component.

32. Sympathetic and Parasympathetic “tone” Continual basal activity of the sympathetic and parasympathetic systems allows either branch of the ANS to increase or decrease its activity of a stimulated organ Sympathetic tone caused by basal secretion from adrenal medulla

33. Denervation supersensitivity Guyton and Hall fig 60-4

34. “Alarm” or “Stress” Response Large portions of the sympathetic nervous system discharge simultaneously-----this increases the body’s ability to perform vigorous muscle activity Increased arterial pressure Increased blood flow to the skeletal muscles with concurrent decrease blood flow to GI tract, kidneys Increased metabolism Increased blood glucose concentration Increased glycoglysis in liver and muscle Increased muscle strength Increased mental activity Increased rate of blood coagulation

35. Autonomic Reflexes cardiovascular reflexes gastrointestinal reflexes bladder emptying sweating blood glucose concentration sexual reflexes

36. Enteric Nervous System Gastrointestinal tract nervous system Myenteric plexus (auberbach’s) meissner’s plexus (submucosal) Sympathetic and Parasympathetic systems interact with the Enteric System Acetylcholine most often excites and Norepinephrine inhibits