Copyright © 2010 Pearson Education, Inc. Motor (efferent) system  Divided into:  Somatic motor division that controls skeletal muscle  Visceral/autonomic – controls smooth and cardiac muscles and the glands (exocrine and endocrine)  These 2 system differ not only in the effector but also in their descending pathway and the response

Copyright © 2010 Pearson Education, Inc. ANS Versus Somatic Nervous System (SNS)  The ANS differs from the SNS in the following three areas  1. Effectors  The effectors of the SNS are skeletal muscles  The effectors of the ANS are cardiac muscle, smooth muscle, and glands

Copyright © 2010 Pearson Education, Inc. ANS Versus Somatic Nervous System (SNS)  2. Efferent pathways  In the SNS heavily myelinated axons of the somatic motor neurons extend from the CNS to the effector (one neuron)  Efferent pathways in the ANS are a two-neuron chain  The preganglionic (first) neuron has a lightly myelinated axon  The post-ganglionic (second) neuron extends to an effector organ Pre-ganglionic Ganglion Post-ganglionic

Copyright © 2010 Pearson Education, Inc.  3. Target organ responses  All somatic motor neurons release Acetylcholine (ACh), which has an excitatory effect  In the ANS:  Preganglionic fibers release ACh  Postganglionic fibers release norepinephrine or ACh and the effect is either stimulatory or inhibitory  ANS effect on the target organ is dependent upon the neurotransmitter released and the receptor type of the effector ANS Versus Somatic Nervous System (SNS)

Copyright © 2010 Pearson Education, Inc. Autonomic Nervous SystemSomatic Nervous SystemCharacteristic Smooth muscle, Cardiac Muscle, Glands Voluntary (skeletal) muscleEffectors Adjustment within the internal environment (homeostasis) Adjustment to external environment. General function 21 Number of neurons from CNS to effectors Chain ganglia, collateral ganglia or terminal ganglia 0 Ganglia outside the CNS Acetylcholine, adrenaline, noradrenalin AcetylcholineNeurotransmitter On NMJ - nicotinic receptors – ACh always excitatory

Copyright © 2010 Pearson Education, Inc. Receptors for neurotransmitters in the motor division  Receptors are divided into 2 groups:  Cholinergic – receive and respond to acetylcholine (ACh):  Two subgroups that are names of chemicals that mimic some of the actions of Ach:  Muscarinic (chemical found in the mushroom Amanita muscarina)  Nicotinic (chemical found in the tobacco plant – nicotina tabacum)  Adrenergic – receive and respond to norepinephrin (NE) / epinephrine (E)  Divided into alpha and beta

Copyright © 2010 Pearson Education, Inc. Cholinergic Nicotinic Receptors location  Motor end plates of skeletal muscle cells (will be discussed later)  All ganglionic neurons (sympathetic and parasympathetic)  Hormone-producing cells of the adrenal medulla  Effect of ACh at nicotinic receptors is always direct and stimulatory

Copyright © 2010 Pearson Education, Inc. Cholinergic Muscarinic Receptors location  All effector cells stimulated by postganglionic cholinergic fibers  The effect of ACh at muscarinic receptors  Can be either inhibitory or excitatory  Depends on the receptor type of the target organ

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. Adrenergic Receptors  Two types  Alpha (  ) (subtypes  1,  2) – excited  Beta (  ) (subtypes  1,  2,  3)  Effects of NT depend on which subclass of receptor predominates on the target organ  Norepinephrine excites mainly Alpha (  ) receptors  Epinephrine excites both alpha and beta equally

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. Enteric nervous system Divisions of the ANS

Copyright © 2010 Pearson Education, Inc. Autonomic Nervous System (ANS) function  The ANS major function is to maintain homeostasis  The ANS :  functions via visceral (subconscious) reflexes  The autonomic system is coordinated primarily by the hypothalamus and the medulla (higher centers)  The brain stem and the spinal cord seem to have direct influence over autonomic functions

Copyright © 2010 Pearson Education, Inc. Autonomic reflexes  Autonomic reflexes are mediated by neural circuits in the spinal cord and brain stem  The afferent pathways include both visceral and somatic fibers  The reflex includes interneurons that receive convergent input from visceral and somatic fibers  Efferent pathway can be sympathetic or parasympathetic  Main difference: visceral reflex arc has two neurons in the motor pathway

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.

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. Para sympathetic functions

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.

Figure 14.4 Cranial Outflow Sacral Outflow

Copyright © 2010 Pearson Education, Inc. Copyright © The McGraw-Hill Companies, Inc (nACh) (mACh) Parasympathetic pre and post-ganglionic receptors

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. 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.

Copyright © 2010 Pearson Education, Inc. Sympathetic division anatomy  The preganglionic cell bodies are located in the lateral horn of segments T1 and L2 (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

1 2

Copyright © 2010 Pearson Education, Inc. 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. Figure & 2 3

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.

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

Copyright © 2010 Pearson Education, Inc. More ANS neurotransmitters FunctionsTransmitter parasympathetic - important in erection and in gastric emptying. Activates guanylate cyclase. nitric oxide (NO) parasympathetic - co-release with ACh affects salivation; also in sympathetic cholinergic fibres. May be important throughout the gastrointestinal tract. vasoactive intestinal polypeptide (VIP) sympathetic - blood vessels and vas deferens. Co-released with catecholamines.adenosine triphosphate (ATP) sympathetic - facilitates effect of noradrenaline (co-released). Causes prolonged vasoconstriction. neuropeptide Y (NPY) important in enteric neurones (peristalsis)serotonin (5HT) enteric.gamma-amino butyric acid (GABA) May mediate vasodilatation in the kidneydopamine co-transmitter with ACh in sympathetic ganglia. gonadotropin releasing hormone (GnRH) sympathetic ganglia, enteric neuronesSubstance P contributes to neurogenic inflammation calcitonin gene related peptide (CGRP)

Copyright © 2010 Pearson Education, Inc. Sympathetic presynaptic nerve terminal parasympathetic nerve terminal 22 22  11 22 11 NE ACh NT-receptor interaction - heart