Copyright © 2010 Pearson Education, Inc. Enteric nervous system Divisions of the ANS

Copyright © 2010 Pearson Education, Inc. The 2 divisions of the ANS exit the spinal cord in different regions  There are 2 anatomical differences between the 2 branches:  The point of origin in the CNS  Location of autonomic ganglia

Copyright © 2010 Pearson Education, Inc. DivisionOrigin of FibersLength of Fibers Location of Ganglia SympatheticThoraco -lumbar region of the spinal cord Short pre - ganglionic and long post - ganglionic Close to the spinal cord Para- sympathetic Brain and sacral spinal cord Long preganglionic and short postganglionic In the visceral effector organs Anatomy of ANS

Copyright © 2010 Pearson Education, Inc. “Rest and digest”

Copyright © 2010 Pearson Education, Inc. The functions of the parasympathetic division  It is also called the anabolic division  The functions center on  Relaxation  Food processing  Energy absorption

Copyright © 2010 Pearson Education, Inc. The major effects of the parasympathetic division  Constriction of pupils  Increase secretion of salivary, gastric, duodenal and intestinal glands, pancreas (both exocrine and endocrine) and liver  Increase of digestive system movement (smooth muscle)  Stimulation of defecation  Contraction of urinary bladder  Constriction of respiratory passageways  Reduction of heart rate and force of contraction

Copyright © 2010 Pearson Education, Inc. Parasympathetic Division Outflow Cranial Outflow Cranial NerveGanglion Effector Organ(s) Effect on effector Occulomotor (III)CiliaryEye (iris) Constrict pupil Facial (VII) Pterygopalatin Submandibular Salivary, nasal, and lacrimal glands Increase secretion Glossopharyngeal (IX) Otic Parotid salivary glands Increase secretion Vagus (X) Located within the walls of target organs Heart, lungs, and most visceral organs Decrease HR, constrict bronchioles Sacral Outflow S 2 -S 4 Located within the walls of the target organs Large intestine, urinary bladder, ureters, and reproductive organs Increase motility and secretion of the GI tract, release of urine, erection

Copyright © 2010 Pearson Education, Inc.

Occulomotor - III

Copyright © 2010 Pearson Education, Inc. Facial nerve - VII

Copyright © 2010 Pearson Education, Inc. Glossopharyngeal - IX

Copyright © 2010 Pearson Education, Inc. Vagus - X

Copyright © 2010 Pearson Education, Inc.

Copyright © The McGraw-Hill Companies, Inc (nACh) (mACh) Parasympathetic pre and post-ganglionic receptors

Copyright © 2010 Pearson Education, Inc. ACh (cholinergic) receptors Nicotinic receptors (nACh) Pre-ganglionic Muscarinic receptors (mACh) Post-ganglionic Direct mechanism – open Na+ channels (depolarization) Fast excitatory effect Indirect mechanism – use of G-protein and 2 nd messenger system Slow excitatory M1, M3, M5 Slow inhibitory M2, M4 Inhibition of adenylate cyclase Increase intracellular Ca 2+ release

Copyright © 2010 Pearson Education, Inc. Break down of ACh  The effect of ACh is short-lived  Inactivated in the synapse by the enzyme acetylcholinesterase (AChE)  Inactivated in the surrounding tissues cholinesterase  The effect of the parasympathetic division is localized and lasts about 20 msec.

Copyright © 2010 Pearson Education, Inc.

Parasympathetic drugs  Modes of action:  direct agonistic action on the receptor (pilocarpine and methacholine)  Indirect agonists work by inactivation of acetylcholinesterase (enzyme that breaks down acetylcholine), resulting in accumulation of acetylcholine in synaptic cleft  antagonist drugs (for example atropine) block the muscarinic receptors and thus block the action of Ach

Copyright © 2010 Pearson Education, Inc. Drugs affecting the parasympathetic nervous system  Nicotinic receptors:  Agonists at muscles will cause contraction  Antagonists at muscles will cause paralysis.  Muscarinic receptors:  Agonists will cause increased bowel and bladder function, decreased HR, bronchoconstriction, and miosis.  Antagonists will cause constipation, urinary retention, increased heart rate, bronchodilation, and dilated pupils

Copyright © 2010 Pearson Education, Inc. Pilocarpine  Cholinergic receptor agonist with strong postganglionic (muscarinic receptor) stimulation and mild ganglionic (nicotinic receptor) stimulation  Muscarinic receptor stimulation effects:  salivation  intestinal motility  pupil constriction

Copyright © 2010 Pearson Education, Inc.

Sympathetic division functions  Involves E activities – exercise, excitement, emergency, and embarrassment  Increases mental alertness  Increases metabolic rate  Activates energy reserves  Increase respiratory rates and dilate respiratory passageways  Increase heart rate and blood pressure  Activate sweat glands

Copyright © 2010 Pearson Education, Inc.

Sympathetic division anatomy  The preganglionic cell bodies are located in the lateral horn of segments T1 and L2 (L 2 (thoracolumbar outflow).  Ganglionic neurons cell bodies are in 3 locations:  Paired Chain ganglia on both sides of the spinal cord  All preganglionic fibers go through the chain ganglia.  Unpaired Collateral/prevertebral ganglia found anterior to the vertebral column  Adrenal medulla – modified sympathetic ganglion that release NT into the blood

Copyright © 2010 Pearson Education, Inc.

Organization of the sympathetic division After passing through the intervertebral foramen the ventral ramus gives rise to a myelinated white ramus The white ramus carries the preganglionic axons to a sympathetic chain ganglion The preganglionic fibers diverge extensively and can synapse on several ganglionic neurons

Copyright © 2010 Pearson Education, Inc. Sympathetic Trunks and Pathways Figure 14.6 A preganglionic fiber follows one of three pathways upon entering the paravertebral ganglia 1. Synapse with the ganglionic neuron within the same ganglion 2. Ascend or descend the sympathetic chain to synapse in another chain ganglion 3. Pass through the chain ganglion and emerge without synapsing

Copyright © 2010 Pearson Education, Inc. Chain ganglia  2 possible pathways  in both the synapse can be either on the same segment or in a different one (pathways 1 or 2)  postganglionic unmyelinated fibers return via gray ramus to the spinal nerve (about 8% of each spinal nerve fibers are sympathetic postganglionic)  postganglionic fibers innervate structures in the body wall, head, neck and limbs (sweat glands, superficial blood vessels, arrector pilli muscle, skin)  postganglionic unmyelinated fibers do not return but create sympathetic nerves  Those innervate structures in the thoracic cavity

Copyright © 2010 Pearson Education, Inc. 1 2

Collateral ganglia  Postganglionic fibers that follow the third pathway synapse in the collteral/prevertebral ganglia  Those ganglia are not paired and they are found only in the abdominal and pelvic regions  They are close to the spinal cord  As a result the postganglionic fibers are longer than the preganglionic one

Copyright © 2010 Pearson Education, Inc.

Pathways with Synapses in the Adrenal Medulla  Some preganglionic fibers pass directly to the adrenal medulla without synapsing  Upon stimulation, medullary cells secrete norepinephrine and epinephrine into the blood

Copyright © 2010 Pearson Education, Inc.

Copyright © The McGraw-Hill Companies, Inc (nACh)   Sympathetic pre and post-ganglionic receptors

Copyright © 2010 Pearson Education, Inc. NE (adrenergic) receptors - all indirect through G-protein 11 11 Slow excitation 2 nd messenger – cAMP Inhibition or activation of adenylate cyclase slow excitation Slow inhibition 22 22 33 Inhibition of adenylate cyclase Lypolysis (excitation) Increase intracellular Ca 2+ release Slow inhibition

Copyright © 2010 Pearson Education, Inc.

Recept or Found inSensitivityEffect  Most sympathetic target tissue NE>ESmooth muscle contraction  Digestive system and pancreas NE>ESmooth muscle contraction  Heart muscle, kidney NE=EHeart muscle contraction  Smooth muscle of some organs E>NESmooth muscle relaxation  Adipose tissueNE>Elipolysis

Copyright © 2010 Pearson Education, Inc. Unique Roles of the Sympathetic Division  only sympathetic fibers are found on:  The adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels  The sympathetic division controls  Thermoregulatory responses to heat  Release of renin from the kidneys and increased blood pressure  Metabolic effects  Increases metabolic rates of cells  Raises blood glucose levels  Mobilizes fats for use as fuels

Copyright © 2010 Pearson Education, Inc. Drugs that act on the sympathetic division  Agonists can work in 2 ways:  Direct -mimic E, NE function on receptors  Indirect – cause release of NE from storage vesicles  Antagonists can:  Prevent synthesis and storage of NE  Block release of NE  Block receptors

Copyright © 2010 Pearson Education, Inc. Example of Drugs affecting the sympathetic nervous system Alpha 1 receptors – agonists will raise BP, antagonists will lower BP Beta 1 receptors – agonists will increase heart rate and strength of contraction, antagonists will decrease heart rate and BP Beta 2 receptors – agonists will increase respiratory airflow, will increase blood flow to skeletal muscles (via blood vessels dilation) antagonists will constrict respiratory flow

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 tone (vasomotor tone)  Keeps the blood vessels in a continual state of partial constriction  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