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AUTONOMIC NERVOUS SYSTEM I

AUTONOMIC NERVOUS SYSTEM I. Dr Margaret Biber January 14, 2009. AUTONOMIC NERVOUS SYSTEM. Involuntary motor system Visceral efferent (motor) system. CENTRAL NERVOUS SYSTEM Brain Spinal Cord PERIPHERAL NERVOUS SYSTEM Somatic N.S. Autonomic N.S.

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AUTONOMIC NERVOUS SYSTEM I

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  1. AUTONOMIC NERVOUS SYSTEM I Dr Margaret Biber January 14, 2009

  2. AUTONOMIC NERVOUS SYSTEM Involuntary motor system Visceral efferent (motor) system

  3. CENTRAL NERVOUS SYSTEM Brain Spinal Cord PERIPHERAL NERVOUS SYSTEM Somatic N.S. Autonomic N.S. Sympathetic Parasympathetic Skeletal Muscle (voluntary muscle) Enteric N.S Heart Smooth Muscle Smooth muscle & Glands Glands of GI tract Not under voluntary control

  4. TARGETS OF INNERVATION BY THE ANS • HEART MUSCLE & specialized conducting tissue • SMOOTH MUSCLE – walls of all hollow organs (except heart) • Blood vessels • Digestive tract • Urinary tract • Reproductive organs • Airways • GLANDULAR TISSUE • Sweat glands • Digestive glands • Glands of the respiratory tract

  5. Functions of the ANS: Regulation of visceral organ function EXAMPLES • CV system: Arterial blood pressure • Diameter of blood vessels • Mechanical performance of the heart: heart rate, force of contraction • Digestive system: controls & coordinates gastrointestinal motility and secretions (in conjunction with hormones) • Emptying of the urinary bladder • Respiratory tract secretions and airway resistance (diameter of bronchi and bronchioles) HOMEOSTASIS (maintenance of the internal environment)

  6. Function of the ANS: Adaptive responses to environmental stimuli • Light • Temperature • Threatening stimuli - Stress

  7. Function of the ANS: Adaptive responses to environmental stimuli • Light - constriction of the pupil to bright light (miosis) - dilation of the pupil in low light (mydriasis) • Temperature -cutaneous vasodilation and sweating in a warm environment - cutaneous vasoconstriction and goose pimpling in the cold • Stress - rapid, coordinated response to threatening or stressful stimuli

  8. FEAR

  9. SIGNS OF FEAR • POUNDING HEART – heart rate & force of contraction increases • DILATED PUPILS – wide eyed with fear • PALLOR – pale with fear – ashen faced • GOOSEPIMPLING – hair standing on end; chills down the spine • COLD SWEAT – clammy hands • DRY MOUTH

  10. STAY AND FIGHT

  11. TAKE TO YOUR HEELS IN FLIGHT

  12. FIGHT OR FLIGHT RESPONSE • Anticipatory – triggered the moment the possibility of trouble is detected • Allows immediate & sustained physical exertion • Critical for survival

  13. SUMMARY OF FUNCTION OF ANS • Exerts overall control of function of visceral organs – key contribution to homeostasis • Produces important adaptations to environmental stimuli: • Level of illumination • Ambient temperature • Stressful, alarming or dangerous situations • Proper function essential for survival

  14. Characteristics of autonomic control

  15. 1. Speed of onset • heart rate can double within 3-5 seconds • sweating can occur within a few seconds to a rise in temperature or in response to fear (cold sweat). • goose pimpling appears in seconds in cold or fearful situations • involuntary emptying of the bladder, when it occurs, does so in seconds • marked changes in blood pressure (rise or fall) can take place in about 5 secs. A precipitous fall in blood pressure causes fainting.

  16. 2. Tonic activity • Basal rate of neuronal firing - sympathetic or parasympathetic tone. • Consists of low frequency bursts of action potentials averaging ~ 1 Hz (impulses per sec). • Sets up a baseline level of effector organ activity • Permits basal activity to be increased or decreased.

  17. 3. Reflex control of autonomic activity • Not under voluntary control • Reflexes are stereotyped responses triggered by specific sensory stimuli • Sensory stimuli that trigger autonomic reflexes do not reach consciousness • Autonomic reflexes are sensitive to & altered by emotional state

  18. ORGANIZATION OF THE ANS Physiological Anatomy

  19. Somatic motor neuron Spinal cord Alpha motor neurons: Axons: Wide diameter, myelinated; Conduct APs at high speeds 15-50 m/sec& at high frequency.  Fast precise control of skeletal muscle Skeletal muscle

  20. Autonomic neurons Spinal cord preganglionic postganglionic Fine axons: Conduct APs at low speeds (0.5 m/sec) & at low frequency (~20 Hz) smooth muscle glands, heart Control of targets slower & much less precise

  21. FIG 1 P 174

  22. Fig 2 P 175

  23. FIG 1

  24. Fig 2 Diffusely distributed targets

  25. FIG 1 Diffusely distributed targets

  26. FIG 1 1. Cervical ganglia are fused Diffusely distributed targets 2. Prevertebral or collateral ganglia (coeliac, superior & inferior mesenteric ganglia) innervate abdominal organs& the enteric NS 3. Preganglionic sympathetic nerves innervate adrenal medullary chromaffin cells (= modified postganglionic sympathetic neurons)

  27. Synaptic Organization of Sympathetic Ganglia: Divergence Spinal cord Sympathetic ganglion Postganglionic nerve Sympathetic chain Preganglionics

  28. Synaptic Organization of Sympathetic Ganglia:Convergence Spinal cord Sympathetic ganglion Postganglionic nerve Sympathetic chain Preganglionic nerve

  29. Divergence and Convergence at the level of single neurons Divergence Convergence Post Pre

  30. ANATOMICAL FEATURES OF THE SYMPATHETIC NS • Thoraco-lumbar outflow • Short preganglionic axon • Long postganglionic axon • Distinct ganglion system with much divergence and convergence of inputs

  31. Fig 3

  32. Key Features of Parasympathetic • Postganglionic nerves lie in or near target tissues  • Long pre, short • postganglionic neurons • Ratio of pre to postganglionic • neurons 1:1 or 1: 2 • Control is highly targeted

  33. ANATOMICAL FEATURES OF THE PARASYMPATHETIC NS • Cranial-sacral outflow • Relatively long preganglionic axon • Little branching of preganglionic axons (little divergence) • Ganglion, if present, located at or near target organ (cranial region) • Short postganglionic axon

  34. post pre Parasympathetic Cranial Spinal cord pre T1 post Sympathetic pre Adrenal Splanchnic nerve L3 Parasympathetic post Sacral pre S2 S3 S4 Schematic ANS

  35. Organization of the Autonomic Neuroeffector Junction

  36. Skeletal NMJ Autonomic NEJ Motor unit

  37. POSTGANGLIONIC

  38. Sympathetic postganglionic nerve terminal: Branching terminal network with varicosities Synaptic vesicle

  39. COMPARISON OF SOMATIC AND AUTONOMIC NERVOUS SYSTEMS SOMATIC AUTONOMIC Target: skeletal muscle smooth muscle heart glands Control: precise; rapid (msecs) less so (100 msecs to secs) Anatomy: one neuron two neurons Properties of motor neurons: wide diameter fine diameter myelinated 2nd neuron unmyelinated rapidly conducting slow conducting 15 - 50 m/sec 0.5 m/sec Ach/NE Ach Ach Skeletal Muscle fiber Motor neuron NMJ Pre Post NEJ

  40. COMPARISON OF SOMATIC AND AUTONOMIC NERVOUS SYSTEMS SOMATIC AUTONOMIC Neuroeffector junction: well organized branching, diffuse terminals nerve terminals close to with variable distances from muscle endplate effector cell membrane (80 - (15 nm gap) 1000 nm) Ach receptors tightly receptors not organized into a packed in endplate localized chemosensitive area Receptors: ligand gated ion channels G-protein coupled signaling on the effector cells Transmitter: acetylcholine acetylcholine - parasympathetic norepinephrine- sympathetic (exception generalized sweat glands) Effects: excitation excitation or inhibition one to one relay modulatory

  41. END

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