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  1. 1. AUTONOMIC NERVOUS SYSTEM Prof. Vajira Weerasinghe Professor of Physiology
  2. 2. 4 Autonomic nervous system The autonomic nervous system is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control
  3. 3. Autonomic (visceral motor) autonomic somatic this dorsal root ganglion is sensory Somatic motor
  4. 4. Difference between somatic motor and autonomic motor ► Somatic motor:  Cell bodies of motor neurons reside in CNS (brain or spinal cord)  Their axons (sheathed in spinal nerves) extend all the way to their skeletal muscles  Fast neural transmission ► Autonomic system: chains of two neurons  1st = preganglionic neuron (in brain or cord)  2nd = postgangionic neuron (cell body in ganglion outside CNS)  Slower because lightly or unmyelinated 6
  5. 5. 7 ►Axon of 1st (preganglionic) neuron leaves CNS to synapse with the 2nd (postganglionic) neuron ►Axon of 2nd (postganglionic) neuron extends to the organ it serves Diagram contrasts somatic (lower) and autonomic: autonomic somatic Note: the autonomic ganglion is motor this dorsal root ganglion is sensory
  6. 6. Divisions of the autonomic nervous system ►Parasympathetic division ►Sympathetic division Serve most of the same organs but cause opposing or antagonistic effects cervical, thoracic, lumbar, sacral
  7. 7. 9 Where they come from Parasympathetic: craniosacral Sympathetic: thoracolumbar
  8. 8. 10 Sympathetic nervous system “fight or flight” ► Also called thoracolumbar system: all its neurons are in lateral horn of gray matter from T1-L2 ► Lead to every part of the body (unlike parasymp.)  Easy to remember that when nervous, you sweat; when afraid, hair stands on end; when excited blood pressure rises (vasoconstriction): these sympathetic only  Also causes: dry mouth, pupils to dilate, increased heart & respiratory rates to increase O2 to skeletal muscles, and liver to release glucose ► Norepinephrine (noradrenaline) is neurotransmitter released by most postganglionic fibers (acetylcholine in preganglionic): “adrenergic”
  9. 9. 11 Sympathetic
  10. 10. 12 Parasympathetic nervous system “rest & digest” ►Also called the craniosacral system because all its preganglionic neurons are in the brain stem or sacral levels of the spinal cord  Cranial nerves III,VII, IX and X  In lateral horn of gray matter from S2-S4 ►Only innervate internal organs (not skin) ►Acetylcholine is neurotransmitter at end organ as well as at preganglionic synapse: “cholinergic”
  11. 11. 13 Parasympathetic continued ► Cranial outflow  III - pupils constrict  VII - tears, nasal mucus, saliva  IX – parotid salivary gland  X (Vagus n) – visceral organs of thorax & abdomen: ►Stimulates digestive glands ►Increases motility of smooth muscle of digestive tract ►Decreases heart rate ►Causes bronchial constriction ► Sacral outflow (S2-4): form pelvic splanchnic nerves  Supply 2nd half of large intestine  Supply all the pelvic (genitourinary) organs
  12. 12. 14 Parasympathetic
  13. 13. Neurotransmitters ►Somatic = all motor neurons release ACH which is always stimulatory ►Visceral = ACH & norepinephrine  All preganglionic fibers release ACH  All postganglionic PsNS fibers release ACH  Most postganglionic SNS fibers release norepi  Can be stimulatory or inhibitory based on receptor types
  14. 14. Comparison of Sympathetic and parasympathetic Systems
  15. 15. Divisions of the ANS ► Sympathetic NS ► Parasymathetic NS ► Dual innervation  Opposing effects on the same organ ► SNS is usually stimulatory (fight or flight) ► PsNS is usually inhibitory (body maint. & conservation of E
  16. 16. Sympathetic nervous system ► The sympathetic division is the “fight-or-flight” system ► Involves E activities – exercise, excitement, emergency, and embarrassment ► Non-essential activities are dampened (GI/urinary) ► 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  Bronchioles dilate…increasing ventilation, delivering more oxygen to cells  Constriction of visceral & cutaneous bv’s (blood is shunted to skeletal mm)  Liver releases more glucose into blood to provide more readily avail. E  Targets adipocytes for lipolysis
  17. 17. Parasympathetic nervous system ► Salivation, Lacrimation, Urination, Digestion, Defecation ► Most active in non-stressful situations ► Concerned with keeping body energy use low ► Lenses of eyes accommodated for near vision ► 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
  18. 18. Differences Ach (N) Ach (N) Ach (M) Nor Sympathetic Parasympathetic Adre
  19. 19. Neurotransmitters and Receptors ► Acetylcholine (ACh) and norepinephrine (NE) are the two major neurotransmitters of the ANS ► ACh is released by all preganglionic axons and all parasympathetic postganglionic axons ► Cholinergic fibers – ACh-releasing fibers ► Adrenergic fibers – sympathetic postganglionic axons that release NE ► Neurotransmitter effects can be excitatory or inhibitory depending upon the receptor type
  20. 20. Cholinergic Receptors ►The two types of receptors that bind ACh are nicotinic and muscarinic ►These are named after drugs that bind to them and mimic ACh effects
  21. 21. Nicotinic Receptors (cholinergic) ►Nicotinic receptors are found on:  Motor end plates (somatic targets)  All ganglionic neurons of both sympathetic and parasympathetic divisions  The hormone-producing cells of the adrenal medulla ►The effect of ACh binding to nicotinic receptors is always stimulatory
  22. 22. Muscarinic Receptors (cholinergic) ►Muscarinic receptors occur on all effector cells stimulated by postganglionic cholinergic fibers ►The effect of ACh binding:  Can be either inhibitory or excitatory  Depends on the receptor type of the target organ
  23. 23. Adrenergic Receptors ► The two types of adrenergic receptors are alpha and beta ► Each type has two or three subclasses ( 1, 2, 1, 2 , 3) ► Effects of NE binding to:  receptors is generally stimulatory  receptors is generally inhibitory ► A notable exception – NE binding to receptors of the heart is stimulatory
  24. 24. Adrenergic Receptors ►Norepinephrine produces its effects by combining with adrenergic receptors  Alpha  Beta
  25. 25. Adrenergic Receptors ►Found in:  Cardiovascular  Endocrine  Gastrointestinal  Genitourinary  Respiratory  Ocular
  26. 26. Alpha Receptors ►Alpha 1: adrenergic receptors located on postsynaptic effector cells.  Smooth muscles of blood vessels: Constriction ►Arteriolar constriction  Bladder sphincter  Penis  Uterus  Pupillary muscles of iris
  27. 27. Alpha 2 ►Same as the Alpha 1 but are located in the presynaptic nerve terminals.
  28. 28. Adrenergic Receptor ►Beta 1 ►Cardiovascular  Cardiac muscle: increased contractility increased force of contraction  Atrioventricular node: increased heart rate  Sinoatrial node: increase in heart rate ►Endocrine  Pancreas
  29. 29. Beta 1 Drugs ►Predominately works on vascular smooth muscle of the heart.
  30. 30. Adrenergic Receptor ►Beta 2 ►Cardiovascular  Dilation of blood vessels ►Endocrine ►Uterine relaxation ►Respiratory: dilation of bronchial muscles
  31. 31. Heart ►Direct stimulation of receptors  Alpha 1 – ►Vasoconstriction of blood vessels which increases blood pressure ►Pressor or vasopressor effect to maintain blood pressure  Beta 1 ►Increased force of myocardial contraction ►Increased speed of electrical conduction in the heart.
  32. 32. Sympathetic vs parasympathetic ►Distribution on different organs ►Actions on different organs ►Drugs acting on receptors ►Reflexes in different systems
  33. 33. Sympathetic vs parasympathetic ►Distribution on different organs
  34. 34. Fig. 9.6
  35. 35. Sympathetic (Thoracolumbar) Division ► Preganglionic cell bodies in lateral horns of spinal cord T1-L2: thoracolumbar ► Preganglionic axons pass through ventral roots to white rami communicantes to the retroperitoneal sympathetic chain ganglia
  36. 36. Parasympathetic (Craniosacral) Division ► Preganglionic cell bodies in nuclei of brainstem or lateral parts of spinal cord gray matter from S2-S4  Preganglionic axons from brain pass to terminal ganglia through cranial nerves III, VII, IX and X  Preganglionic axons from sacral region pass through pelvic nerves to terminal ganglia ► Terminal ganglia located near organ innervated or embedded in wall of organ
  37. 37. Sympathetic vs parasympathetic ►Actions on different organs
  38. 38. Sympathetic vs parasympathetic ►Drugs acting on receptors
  39. 39. Parasympathetic Sympathetic
  40. 40. salbutamol
  41. 41. Sympathetic vs parasympathetic ►Reflexes in different systems
  42. 42. ANS reflexes ► CVS:  baroreceptor reflex  Control of heart rate  chemoreceptor reflex ► GIT:  GIT secretions and motility ► Other:  Urinary bladder control  Sexual reflexes  Sweating  Other visceral reflexes
  43. 43. Exception – adrenal medulla
  44. 44. 52 Adrenal glands On top of kidneys Adrenal medulla (inside part) is a major organ of the sympathetic nervous system
  45. 45. 53 Adrenal gland is an exception ►Synapse in gland ►Can cause body-wide release of epinephrine (adrenaline) and norepinephrine (noradrenaline) in an extreme emergency (adrenaline “rush” or surge)
  46. 46. Innervation Ach
  47. 47. Another exception - Sweat glands ► The sweat glands are innervated by the sympathetic nervous system (part of the fight or flight response system) ► Preganglionic neuron is short, originates from the thoracolumbar region of the spinal cord, uses acetylcholine as its neurotransmitter (nicotinic ) ► Postganglionic neuron for sweat gland innervation differs from other sympathetic postganglionic neurons in that it releases acetylcholine to act on muscarinic receptors
  48. 48. Another exception – skeletal muscle blood vessels ►These are also innervated by sympathetic cholinergic fibres
  49. 49. 58 Summary

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