Autonomic Nervous System


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Autonomic Nervous System

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Autonomic Nervous System

  1. 1. The Autonomic Nervous System Moderator Dr. Gangaram
  2. 2. Introduction The critical component of central network involved in homeostasis & adaptation 3 subdivisions : ●Sympathetic Nervous System ●Parasympathetic Nervous System ●Enteric Nervous System
  3. 3. To repeat… ANS is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control ●Visceral motor innervates non-skeletal (non-somatic) muscles ●Composed of a special group of neurons serving: ● ● ● ● ● Cardiac muscle (the heart) Smooth muscle (walls of viscera and blood vessels) Internal organs Skin 4
  4. 4. Divisions of the autonomic nervous system Parasympathetic division ● Sympathetic division ● Serve most of the same organs but cause opposing or antagonistic effects Parasysmpathetic: routine maintenance “rest &digest” Sympathetic: mobilization & increased metabolism “fight, flight or fright” or “fight, flight or freeze” 5
  5. 5. Basic anatomical difference between the motor pathways of the voluntary somatic nervous system (to skeletal muscles) and those of the autonomic nervous system Somatic division: ● ● ● 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 Autonomic system: chains of two motor neurons ● ● ● ● 1st = preganglionic neuron (in brain or cord) 2nd = ganglionic neuron (cell body in ganglion outside CNS) Slower because lightly or unmyelinated 6
  6. 6. ● ● Axon of 1st (preganglionic) neuron leaves CNS to synapse with the 2nd (ganglionic) neuron Axon of 2nd (ganglionic) neuron extends to the organ it serves Diagram contrasts somatic (lower) and autonomic: autonomic this dorsal root ganglion is sensory somatic 7 Note: the autonomic ganglion is motor
  7. 7. Anatomical Differences in Sympathetic and Parasympathetic Divisions Length of postganglionic fibers – Sympathetic – long postganglionic fibers – Parasympathetic – short postganglionic fibers Branching of axons – Sympathetic axons – highly branched – Influences many organs – Parasympathetic axons – few branches – Localized effect 8
  8. 8. C o p y ri g h © 2 0 0 5 P e a r s o n E d u c a i Anatomical Differences in Sympathetic and Parasympathetic Divisions
  9. 9. C o p y ri g h © 2 0 0 5 P e a r s o n E d u c a i Anatomical Differences in Sympathetic and Parasympathetic Divisions
  10. 10. Comparison of Somatic and Autonomic Nervous Systems Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
  11. 11. Sympathetic nervous system continued Regardless of target, all begin same ● Preganglionic axons exit spinal cord through ventral root and enter spinal nerve ● Exit spinal nerve via communicating ramus ● Enter sympathetic trunk/chain where postganglionic neurons are ● Has three options… ● 12
  12. 12. Options of preganglionic axons in sympathetic trunk Synapse on postganglionic neuron in chain ganglion then return to spinal nerve and follow its branch to the skin ● Ascend or descend within sympathetic trunk, synapse with a posganglionic neuron within a chain ganglion, and return to spinal nerve at that level and follow branches to skin ● Enter sympathetic chain, pass through without synapsing, form a splanchnic nerve that passes toward thoracic or abdominal organs ● These synapses in prevertebral ganglion in front of aorta ● Postganglionic axons follow arteries to organs ● 13
  14. 14. C o p y ri g h Sympathetic Pathways to Periphery © 2 0 0 5 P e a r s o n E d u c a i Figure 15.9
  15. 15. C o p y ri g h © 2 0 0 5 P e a r s o n E d u c a i Sympathetic Pathways to the Head
  16. 16. C o p y ri g h © 2 0 0 5 P e a r s o n E d u c a i Sympathetic Pathways to the Abdominal Organs
  17. 17. C o p y ri g h © 2 0 0 5 P e a r s o n E d u c a i Sympathetic Pathways to the Pelvic Organs
  18. 18. The Role of the Adrenal Medulla in the Sympathetic Division Major organ of the sympathetic nervous system Secretes great quantities epinephrine (a little norepinephrine) Stimulated to secrete by preganglionic sympathetic fibers
  19. 19. C o p y ri g h © 2 0 0 5 P e a r s o n E d u c a i The Adrenal Medulla
  20. 20. C o p y ri g h © 2 0 0 5 P e a r s o n E d u c a i Sympathetic Division of the ANS
  21. 21. C o p y ri g h © 2 0 0 5 P e a r s o n E d u c a i The Parasympathetic Division
  22. 22. Cranial Outflow Preganglionic fibers run via: – Oculomotor nerve (III) – Facial nerve (VII) – Glossopharyngeal nerve (IX) – Vagus nerve (X) Cell bodies located in cranial nerve nuclei in the brain stem
  23. 23. Westphal nucleus is a part of occulomotor complex in midbrain – sends preganglionic axons that occupy peripheral portion of the occulomotor nerve and synapse on the neurons of ciliary ganglion in the orbit ● These neurons innervate iris and ciliary muscles ● Eliciting pupil constriction, accomodation of eye ●
  24. 24. Superior salivatory nucleus – ● In pons ● projects via facial nerve to sphenopalatine ganglion, which innervates - lacrimal gland ( lacrimation ) cerebral blood vessels ( vasodilatation ) ● to submandibular ganglion – secretomotor & vasodilator inputs to corresponding salivary glands ●
  25. 25. Inferior salivatory nucleus – ● In medulla ● Sends axons via glossopharyngeal nerve ● Synapse on Otic ganglion ● Stimulate parotid gland secretion ●
  26. 26. Outflow via the Vagus Nerve (X) Fibers innervate visceral organs of the thorax and most of the abdomen Stimulates - digestion, reduction in heart rate and blood pressure Preganglionic cell bodies Located in dorsal motor nucleus in the medulla Ganglionic neurons – – Confined within the walls of organs being innervated
  27. 27. Vagus innervates heart, respiratory tract and entire gastrointestinal tract except descending colon and rectum ● Most vagal preganglionic neurons – situated in dorsal motor nucleus of vagus provides input to git and respiratory tracts, heart ● Vagal preganglionic output to heart - Neurons in ventrolateral portion of nucleus ambiguus ● Vagus – cardioinhibitory, visceromotor and secretomotor effects ●
  28. 28. 9 Sacral Parasympathetic Outflow • Consists of S2-S4. • Pelvic splanchnic nerves
  29. 29. Sacral preganglionic output – Arises from neurons of sacral preganglionic nucleus located in lateral gray matter of spinal segments S2 & S3 ● Their axons pass via ventral roots of pelvic splanchnic nerves which join inferior hypogastric plexus ● Innervate colon, bladder, sexual organs ● Parasympathetic output – contraction of bladder detrussor muscle & circular smooth muscle of rectum. ●
  30. 30. Sacral parasympathetic output elicits Vasodilatation of cavernous tissue of penis required for penile erection , whereas sympathetic output controls ejaculation ●
  31. 31. 2 Autonomic Plexuses • A network of sympathetic and parasympathetic axons. • Cardiac plexus- heart. • Pulmonary plexus- the bronchial tree. • Celiac plexus- largest. Supplies the stomach, spleen, pancreas, liver, gallbladder, and adrenal medullae.
  32. 32. 3 Autonomic Plexuses (Cont’d).. • Superior mesenteric plexus- small intestine and proximal colon. • Inferior mesenteric plexus- distal colon and rectum. • Hypogastric plexus- urinary bladder and genital organs. • Renal plexus- kidneys and ureters.
  33. 33. Enteric Nervous System Includes several types of sensory neurons, inter-neurons, motor neurons – which form integrative local reflex circuits ● Controlling motility, secretion, blood flow throughout the gut ● The activity of enteric nervous system is largely independent of extrinsic innervation but is modulated by both vagal inputs from dorsal vagal nucleus and sympathetic inputs from prevertebral ganglia ●
  34. 34. 5 Integration and Control of Autonomic Functions • Direct innervation- brain stem and spinal cord. • Hypothalamus is the major control and integration center of the ANS. • It receives input from the limbic system.
  35. 35. Central control of the Autonomic NS Amygdala: main limbic region for emotions -Stimulates sympathetic activity, especially previously learned fearrelated behavior -Can be voluntary when decide to recall frightful experience - cerebral cortex acts through amygdala -Some people can regulate some autonomic activities by gaining extraordinary control over their emotions Hypothalamus: main integration center Reticular formation: most direct influence over autonomic function 36
  36. 36. Components Telencephalic structures –insular cortex ant cingulate cortex Amygdala ● Insular cortex - integration of bodily sensation, emotion, decision making ● anterior cingulate cortex – motivation, goal directed behavior ● amygdala – conditioned fear responses ●
  37. 37. Hypothalamus – central role in integrating autonomic and endocrine responses ● Hypothalmus – critical role in adaptation to internal / external stimuli, while maintaining homeostasis ● 3 zones ● Paraventricular zone – neuroendocrine control via connections to pituitary ● Medial zone – thermoregulation, osmoregulation, food intake, response to stress ● Lateral zone – arousal behaviour, sleep wake cycle ●
  38. 38. Brain Stem Components – ● Periaqueductal gray – ● integration of autonomic, somatic and antinociceptive responses to external stress. ● coordinates cardiovascular, respiratory, thermoregulatory, urinary, reproductive and pain control systems ● Parabrachial nucleus – taste, salivation, gi activity, cardiorespiratory activity, thermoregulation ● NTS – 1st relay center for taste and visceral afferent information carried in CN VII,IX,X And also for all medullary, cvs, rs, gi reflexes ●
  39. 39. Visceral Afferents Inform CNS about Mechanical & Chemical events in internal organs ● This information is conveyed to produce conscious visceral sensation and initiate visceral reflex responses ● Spinal visceral afferents innervate all peripheral organs ● Their cell bodies are in dorsal root ganglion ●
  40. 40. Brain stem visceral afferents are carried primarily by glossopharyngeal and vagus nerves ● Cell bodies in petrosal & nodose ganglia ● All brain stem visceral afferent nerves relay in nucleus of solitary tract ( NTS ) ● NTS is a major site of information integration of many bodily functions ●
  41. 41. Rostral portion of NTS – receives taste afferents via facial nerve( geniculate ganglion ) , glossopharyngeal & vagus nerves ● Intermediate portion – receives gastrointestinal afferents ● Caudal portion of the NTS recieves afferent information from baroreceptors, cardioreceptors, chemoreceptors and pulmonary receptors ●
  42. 42. Anatomical Differences in Sympathetic and Parasympathetic Divisions (Recall) Issue from different regions of the CNS – Sympathetic – also called the thoracolumbar division – Parasympathetic – also called the craniosacral division
  44. 44. Horner's syndrome ● Interruption of sympathetic supply to head and neck ● Constriction of pupil ● Drooping of upper eyelid ● Reduced prominance of eye(enophthalmous) ● anhydrosis
  45. 45. Dysautonomic polyneuropathy ● ● Rare, both sympathetic and parasympathetic are affected at post ganglionic level Somatosensory and motor nerves spared
  46. 46. Orthostatic hypotension Primary ● ● ● Middle aged Post-ganglionic sympathetic Secondary ● ● Parasympathetic spared ● ANS impairment as a part of peripheral neuropathy Afferent pathways or post ganglionic sympathetic fibres in spinal nerves Eg GBS, porphyrias, DM, alcoholic, nutritional Anhydrosis, orthostatic hypotension, impotency, atonicity of bladder
  47. 47. Summary 52
  48. 48. Thank you Dr. Shirisha
  49. 49. Autonomic lab tests : ● impaired sudomotor axon reflex response reduced variation of heart rate to deep breathing reduced valsalva ratio orthostatic hypotension gi motility – delayed gastric emptying usg post void urine – 250 cc