Lecture 5 ans

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Lecture 5 ans

  1. 1. Chapter 15 The Autonomic Nervous System Lecture Outline
  2. 2. INTRODUCTION <ul><li>The autonomic nervous system ( ANS ) operates via reflex arcs. </li></ul><ul><li>Regulate activity of smooth muscle, cardiac muscle & certain glands </li></ul><ul><li>Receives input from limbic system and other regions of the cerebrum </li></ul><ul><li>Operation of the ANS to maintain homeostasis, however, depends on a continual flow of sensory afferent input, from receptors in organs, and efferent motor output to the same effector organs. </li></ul><ul><li>Structurally, the ANS includes autonomic sensory neurons, integrating centers in the CNS, and autonomic motor neurons. </li></ul><ul><li>Functionally, the ANS usually operates without conscious control. </li></ul><ul><li>The ANS is regulated by the hypothalamus and brain stem. </li></ul>
  3. 3. SOMATIC AND AUTONOMIC NERVOUS SYSTEMS <ul><li>The somatic nervous system contains both sensory and motor neurons. </li></ul><ul><li>The somatic sensory neurons receive input from receptors of the special and somatic senses. </li></ul><ul><li>Somatic motor neurons innervate skeletal muscle to produce conscious, voluntary movements. </li></ul><ul><li>The autonomic nervous system contains both autonomic sensory and motor neurons. </li></ul><ul><li>The ANS also receives sensory input from somatic senses and special sensory neurons. </li></ul><ul><li>The autonomic motor neurons regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities of cardiac muscle, smooth muscle, and glands. </li></ul>
  4. 4. Somatic versus Autonomic NS All somatic motor pathways consist of a single motor neuron Autonomic motor pathways consists of two motor neurons in series
  5. 5. Basic Anatomy of ANS <ul><li>Preganglionic neuron </li></ul><ul><ul><li>cell body in brain or spinal cord </li></ul></ul><ul><li>Postganglionic neuron </li></ul><ul><ul><li>cell body lies outside the CNS in an autonomic ganglion </li></ul></ul>
  6. 6. AUTONOMIC NERVOUS SYSTEM <ul><li>The output (efferent) part of the ANS is divided into two principal parts: </li></ul><ul><ul><li>the sympathetic division </li></ul></ul><ul><ul><li>the parasympathetic division </li></ul></ul><ul><ul><li>Organs that receive impulses from both sympathetic and parasympathetic fibers are said to have dual innervation. </li></ul></ul><ul><li>Dual innervation </li></ul><ul><ul><li>one speeds up organ </li></ul></ul><ul><ul><li>one slows down organ </li></ul></ul><ul><ul><li>Sympathetic NS increases heart rate </li></ul></ul><ul><ul><li>Parasympathetic NS decreases heart rate </li></ul></ul>
  7. 7. Sympathetic ANS vs. Parasympathetic ANS
  8. 8. Structures of Sympathetic NS <ul><li>Preganglionic cell bodies at T1 to L2 </li></ul><ul><li>Postganglionic cell bodies </li></ul><ul><ul><li>sympathetic chain ganglia along the spinal column </li></ul></ul><ul><ul><li>prevertebral ganglia at a distance from spinal cord </li></ul></ul><ul><ul><ul><li>celiac ganglion </li></ul></ul></ul><ul><ul><ul><li>superior mesenteric ganglion </li></ul></ul></ul><ul><ul><ul><li>inferior mesenteric ganglion </li></ul></ul></ul>
  9. 9. Organs Innervated by Sympathetic NS <ul><li>Structures innervated by each spinal nerve </li></ul><ul><ul><li>sweat glands, arrector pili mm., blood vessels to skin & skeletal mm. </li></ul></ul><ul><li>Thoracic & cranial plexuses supply: </li></ul><ul><ul><li>heart, lungs, esophagus & thoracic blood vessels </li></ul></ul><ul><ul><li>plexus around carotid artery to head structures </li></ul></ul><ul><li>Splanchnic nerves to prevertebral ganglia supply: </li></ul><ul><ul><li>GI tract from stomach to rectum, urinary & reproductive organs </li></ul></ul>
  10. 10. Anatomy of Parasympathetic NS <ul><li>Preganglionic cell bodies found in </li></ul><ul><ul><li>4 cranial nerve nuclei in brainstem </li></ul></ul><ul><ul><li>S2 to S4 spinal cord </li></ul></ul><ul><li>Postganglionic cell bodies very near or in the wall of the target organ in a terminal ganglia </li></ul>
  11. 11. Parasympathetic Sacral Nerve Fibers <ul><li>Form pelvic splanchnic nerves </li></ul><ul><li>Preganglionic fibers end on terminal ganglia in walls of target organs </li></ul><ul><li>Innervate smooth muscle and glands in colon, ureters, bladder & reproductive organs </li></ul>
  12. 12. ANS Neurotransmitters <ul><li>Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released </li></ul><ul><li>Adrenergic </li></ul><ul><li>Cholinergic </li></ul>
  13. 13. Cholinergic Neurons and Receptors <ul><li>Cholinergic neurons release acetylcholine </li></ul><ul><ul><li>all preganglionic neurons </li></ul></ul><ul><ul><li>all parasympathetic postganglionic neurons </li></ul></ul><ul><ul><li>few sympathetic postganglionic neurons (to most sweat glands) </li></ul></ul><ul><li>Excitation or inhibition depending upon receptor subtype and organ involved. </li></ul>
  14. 14. Cholinergic Neurons and Receptors <ul><li>Cholinergic receptors are integral membrane proteins in the postsynaptic plasma membrane. </li></ul><ul><li>The two types of cholinergic receptors are nicotinic and muscarinic receptors . </li></ul><ul><ul><li>Activation of nicotinic receptors causes excitation of the postsynaptic cell. </li></ul></ul><ul><ul><ul><li>Nicotinic receptors are found on dendrites & cell bodies of autonomic NS cells (and at NMJ.) </li></ul></ul></ul><ul><ul><li>Activation of muscarinic receptors can cause either excitation or inhibition depending on the cell that bears the receptors. </li></ul></ul><ul><ul><ul><li>Muscarinic receptors are found on plasma membranes of all parasympathetic effectors </li></ul></ul></ul>
  15. 15. Adrenergic Neurons and Receptors <ul><li>Adrenergic neurons release norepinephrine (NE) ) </li></ul><ul><ul><li>from postganglionic sympathetic neurons only </li></ul></ul><ul><li>Excites or inhibits organs depending on receptors </li></ul><ul><li>NE lingers at the synapse until enzymatically inactivated by monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT) </li></ul>
  16. 16. Physiological Effects of the ANS <ul><li>Most body organs receive dual innervation </li></ul><ul><ul><li>innervation by both sympathetic & parasympathetic </li></ul></ul><ul><li>Hypothalamus regulates balance (tone) between sympathetic and parasympathetic activity levels </li></ul><ul><li>Some organs have only sympathetic innervation </li></ul><ul><ul><li>sweat glands, adrenal medulla, arrector pili mm & many blood vessels </li></ul></ul><ul><ul><li>controlled by regulation of the “tone” of the sympathetic system </li></ul></ul>
  17. 17. Sympathetic Responses <ul><li>Dominance by the sympathetic system is caused by physical or emotional stress -- “E situations” </li></ul><ul><ul><li>emergency, embarrassment, excitement, exercise </li></ul></ul><ul><li>Alarm reaction = flight or fight response </li></ul><ul><ul><li>dilation of pupils </li></ul></ul><ul><ul><li>increase of heart rate, force of contraction & BP </li></ul></ul><ul><ul><li>decrease in blood flow to nonessential organs </li></ul></ul><ul><ul><li>increase in blood flow to skeletal & cardiac muscle </li></ul></ul><ul><ul><li>airways dilate & respiratory rate increases </li></ul></ul><ul><ul><li>blood glucose level increase </li></ul></ul><ul><li>Long lasting due to lingering of NE in synaptic gap and release of norepinephrine by the adrenal gland </li></ul>
  18. 18. Parasympathetic Responses <ul><li>Enhance “rest-and-digest” activities </li></ul><ul><li>Mechanisms that help conserve and restore body energy during times of rest </li></ul><ul><li>Normally dominate over sympathetic impulses </li></ul><ul><li>SLUDD type responses = salivation, lacrimation, urination, digestion & defecation and 3 “decreases”--- decreased HR, diameter of airways and diameter of pupil </li></ul><ul><li>Paradoxical fear when there is no escape route or no way to win </li></ul><ul><ul><li>causes massive activation of parasympathetic division </li></ul></ul><ul><ul><li>loss of control over urination and defecation </li></ul></ul>
  19. 19. PHYSIOLOGICAL EFFECTS OF THE ANS - Summary <ul><li>The sympathetic responses prepare the body for emergency situations (the fight-or-flight responses). </li></ul><ul><li>The parasympathetic division regulates activities that conserve and restore body energy (energy conservation-restorative system). </li></ul>
  20. 20. Autonomic or Visceral Reflexes <ul><li>A visceral autonomic reflex adjusts the activity of a visceral effector, often unconsciously. </li></ul><ul><ul><li>changes in blood pressure, digestive functions etc </li></ul></ul><ul><ul><li>filling & emptying of bladder or defecation </li></ul></ul><ul><li>Autonomic reflexes occur over autonomic reflex arcs. Components of that reflex arc: </li></ul><ul><ul><li>sensory receptor </li></ul></ul><ul><ul><li>sensory neuron </li></ul></ul><ul><ul><li>integrating center </li></ul></ul><ul><ul><li>pre & postganglionic motor neurons </li></ul></ul><ul><ul><li>visceral effectors </li></ul></ul>
  21. 21. Control of Autonomic NS <ul><li>Not aware of autonomic responses because control center is in lower regions of the brain </li></ul><ul><li>Hypothalamus is major control center </li></ul><ul><ul><li>input: emotions and visceral sensory information </li></ul></ul><ul><ul><ul><li>smell, taste, temperature, osmolarity of blood, etc </li></ul></ul></ul><ul><ul><li>output: to nuclei in brainstem and spinal cord </li></ul></ul><ul><ul><li>posterior & lateral portions control sympathetic NS </li></ul></ul><ul><ul><ul><li>increase heart rate, inhibition GI tract, increase temperature </li></ul></ul></ul><ul><ul><li>anterior & medial portions control parasympathetic NS </li></ul></ul><ul><ul><ul><li>decrease in heart rate, lower blood pressure, increased GI tract secretion and mobility </li></ul></ul></ul>
  22. 22. Autonomic versus Somatic NS - Review <ul><li>Somatic nervous system </li></ul><ul><ul><li>consciously perceived sensations </li></ul></ul><ul><ul><li>excitation of skeletal muscle </li></ul></ul><ul><ul><li>one neuron connects CNS to organ </li></ul></ul><ul><li>Autonomic nervous system </li></ul><ul><ul><li>unconsciously perceived visceral sensations </li></ul></ul><ul><ul><li>involuntary inhibition or excitation of smooth muscle, cardiac muscle or glandular secretion </li></ul></ul><ul><ul><li>two neurons needed to connect CNS to organ </li></ul></ul><ul><ul><ul><li>preganglionic and postganglionic neurons </li></ul></ul></ul>

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