1. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 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  Have viscera as most of their effectors

2. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings ANS in the Nervous System Figure 14.1

3. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings ANS Versus Somatic Nervous System (SNS)  The ANS differs from the SNS in the following three areas  Effectors  Efferent pathways  Target organ responses

4. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Effectors  The effectors of the SNS are skeletal muscles  The effectors of the ANS are cardiac muscle, smooth muscle, and glands

5. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Efferent Pathways  Heavily myelinated axons of the somatic motor neurons extend from the CNS to the effector  Axons of the ANS are a two-neuron chain  The preganglionic (first) neuron has a lightly myelinated axon  The ganglionic (second) neuron extends to an effector organ

6. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Comparison of Somatic and Autonomic Systems Figure 14.2

7. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Divisions of the ANS  ANS divisions: sympathetic and parasympathetic  The sympathetic mobilizes the body during extreme situations  The parasympathetic performs maintenance activities and conserves body energy  The two divisions counterbalance each other

8. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 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

9. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 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

10. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings DivisionOrigin of FibersLength of Fibers Location of Ganglia SympatheticThoracolumbar region of the spinal cord Short preganglionic and long postganglionic Close to the spinal cord ParasympatheticBrain and sacral spinal cord Long preganglionic and short postganglionic In the visceral effector organs Anatomy of ANS

11. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.3

12. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 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 © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.4

14. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sympathetic Outflow  Arises from spinal cord segments T 1 through L 2  Sympathetic neurons produce the lateral horns of the spinal cord  Preganglionic fibers pass through the white rami communicantes and synapse in the chain (paravertebral) ganglia  Fibers from T 5 -L 2 form splanchnic nerves and synapse with collateral ganglia  Postganglionic fibers innervate the numerous organs of the body

15. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.5

16. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sympathetic Trunks and Pathways  The paravertebral ganglia form part of the sympathetic trunk or chain  Typically there are 23 ganglia – 3 cervical, 11 thoracic, 4 lumbar, 4 sacral, and 1 coccygeal

17. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sympathetic Trunks and Pathways Figure 14.6

18. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sympathetic Trunks and Pathways  A preganglionic fiber follows one of three pathways upon entering the paravertebral ganglia  Synapse with the ganglionic neuron within the same ganglion  Ascend or descend the sympathetic chain to synapse in another chain ganglion  Pass through the chain ganglion and emerge without synapsing

19. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pathways with Synapses in Chain Ganglia  Postganglionic axons enter the ventral rami via the gray rami communicantes  These fibers innervate sweat glands and arrector pili muscles  Rami communicantes are associated only with the sympathetic division

20. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pathways to the Head  Preganglionic fibers emerge from T 1 -T 4 and synapse in the superior cervical ganglion  These fibers:  Serve the skin and blood vessels of the head  Stimulate dilator muscles of the iris  Inhibit nasal and salivary glands

21. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pathways to the Thorax  Preganglionic fibers emerge from T 1 -T 6 and synapse in the cervical chain ganglia  Postganglionic fibers emerge from the middle and inferior cervical ganglia and enter nerves C 4 -C 8  These fibers innervate the heart via the cardiac plexus, as well as innervating the thyroid and the skin

22. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pathways to the Thorax  Other T 1 -T 6 preganglionic fibers synapse in the nearest chain ganglia  Postganglionic fibers directly serve the heart, aorta, lungs, and esophagus

23. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pathways with Synapses in Collateral Ganglia  These fibers (T 5 -L 2 ) leave the sympathetic chain without synapsing  They form thoracic, lumbar, and sacral splanchnic nerves  Their ganglia include the celiac, the superior and inferior mesenterics, and the hypogastric

24. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pathways to the Abdomen  Sympathetic nerves innervating the abdomen have preganglionic fibers from T 5 -L 2  They travel through the thoracic splanchnic nerves and synapse at the celiac and superior mesenteric ganglia  Postganglionic fibers serve the stomach, intestines, liver, spleen, and kidneys

25. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pathways to the Pelvis  Preganglionic fibers originate from T 10 -L 2  Most travel via the lumbar and sacral splanchnic nerves to the inferior mesenteric and hypogastric ganglia  Postganglionic fibers serve the distal half of the large intestine, the urinary bladder, and the reproductive organs

26. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pathways with Synapses in the Adrenal Medulla  Fibers of the thoracic splanchnic nerve pass directly to the adrenal medulla  Upon stimulation, medullary cells secrete norepinephrine and epinephrine into the blood

27. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Visceral Reflexes  Visceral reflexes have the same elements as somatic reflexes  They are always polysynaptic pathways  Afferent fibers are found in spinal and autonomic nerves

28. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Visceral Reflexes Figure 14.7

29. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Referred Pain  Pain stimuli arising from the viscera are perceived as somatic in origin  This may be due to the fact that visceral pain afferents travel along the same pathways as somatic pain fibers Figure 14.8

30. Copyright © 2010 Pearson Education, Inc. Receptors for Neurotransmitters 1.Cholinergic receptors for ACh 2.Adrenergic receptors for NE (and epinephrine from adrenal glands)

31. Copyright © 2010 Pearson Education, Inc. Cholinergic Receptors Two types of receptors bind ACh 1.Nicotinic 2.Muscarinic Named after nicotine and muscarine, which bind selectively to the different classes of receptors

32. Copyright © 2010 Pearson Education, Inc. Nicotinic Receptors Found on Motor end plates of skeletal muscle cells (Chapter 9) All ganglionic neurons (sympathetic and parasympathetic) Epinephrine- and NE-secreting cells of the adrenal medulla Effect of ACh at nicotinic receptors is always stimulatory

33. Copyright © 2010 Pearson Education, Inc. Muscarinic Receptors Found on all effector cells stimulated by postganglionic cholinergic fibers Effect of ACh at muscarinic receptors Can be either inhibitory (e.g. at heart) or excitatory (e.g. in eye and in gut) Depends on the receptor type of the target organ

34. Copyright © 2010 Pearson Education, Inc. Muscarinic Receptors in Exercise Not all sympathetic postganglionics secrete NE: Sympathetic postganglionics to skeletal muscle (“sympathetic cholinergic fibers”) secrete ACh(!). Acts at muscarinic receptors in smooth muscle of blood vessels in skeletal muscle to cause vasodilation. Sympathetic cholinergic fibers also act via muscarinic receptors to cause perspiration at eccrine sweat glands. Good for fight-or-flight.

35. 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

36. Copyright © 2010 Pearson Education, Inc. Effects of Drugs Atropine: Anticholinergic (antimuscarinic), blocks parasympathetic effects. Prevent salivation during surgery; dilate pupils for eye exam. (Eye: sympathetics cause pupil dilation, parasymps cause constriction and allow focusing on near objects.) Natural source of atropine: belladonna (beautiful woman) plant, a.k.a. deadly nightshade.

37. Copyright © 2010 Pearson Education, Inc. Effects of Drugs Alpha agonists (e.g. phenylephrine) used as decongestants. Constrict blood vessels in nasal mucosae -> less runny nose… Beta blockers widely used to treat hypertension. Lower heart rate and cardiac contractility. Beta 2 agonists cause bronchiolar dilation, useful for short-term asthma relief. EpiPen TM : Epinephrine activates alpha and beta. Used to block severe allergic reactions and to prevent anaphylactic shock.

38. 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

39. 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

40. Copyright © 2010 Pearson Education, Inc. Sympathetic Tone Increased activity on sympathetic fibers causes blood vessel constriction (in skin & gut, but not in heart and not much in skeletal muscle) and increase in blood pressure Decreased sympathetic activity causes blood vessel dilation and decrease in BP Beta-blocker drugs are used more than alpha blockers to treat hypertension

41. 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 Drugs that block parasympathetic responses increase heart rate and block fecal and urinary retention

42. Copyright © 2010 Pearson Education, Inc. Cooperative Effects Best seen in control of the external genitalia Parasympathetic fibers cause vasodilation; are responsible for erection of the penis or clitoris Sympathetic fibers cause ejaculation of semen in males and reflex contraction of a female’s vagina

43. Copyright © 2010 Pearson Education, Inc. Unique Roles of the Sympathetic Division Adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels receive only sympathetic fibers (no parasympathetics) 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

44. Copyright © 2010 Pearson Education, Inc. Effects of Sympathetic Activation Sympathetic activation is long lasting because NE Is inactivated more slowly than ACh NE and epinephrine are released into the blood by adrenal glands and remain there until destroyed by the liver

45. Copyright © 2010 Pearson Education, Inc. Control of ANS Functioning Hypothalamus—main integrative center of ANS activity Subconscious cerebral input via limbic lobe connections influences hypothalamic function Other controls come from the cerebral cortex, the reticular formation, and the spinal cord

46. Copyright © 2010 Pearson Education, Inc. Figure 14.9 Cerebral cortex (frontal lobe) Limbic system (emotional input) Communication at subconscious level Hypothalamus Overall integration of ANS, the boss Spinal cord Urination, defecation, erection, and ejaculation reflexes Brain stem (reticular formation, etc.) Regulation of pupil size, respiration, heart, blood pressure, swallowing, etc.