autonomic nervous system autonomic nervous system is the part of nervous system that is responsible...

AUTONOMIC NERVOUS SYSTEM

• Autonomic nervous system is the part of nervous system that is responsible for homeostasis

• The word “autonomous” is taken from greek words the autos meaning self & the monos meaning control

• ANS is involuntary system• It collects information about changes in

viscera ,interprets & guides the actions to be executed• Although survival is possible without ANS,ability to

adapt to environmental stressors is severely compromised

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DIVISIONS OF ANS

• SYMPATHETIC DIVISION• Also called

THORACOLUMBAR DIVISION

• Consists of thoracic and lumbar chains of sympathetic ganglia

• PARASYMPATHETIC DIVISION

• Also called CRANIOSACRAL DIVISION

• Consists of sacral ganglia& ganglia associated with 3rd,7th,9th,and 10th cranial nerves

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ANATOMIC ORGANISATION OF AUTONOMIC OUTFLOW

• The final common pathway linking the central nervous system (CNS) to skeletal muscles is the ά motor neuron

• Sympathetic and parasympathetic neurons serve as the final common pathway from the CNS to visceral targets

• The peripheral motor portions of the ANS are made up of two neurons: preganglionic and postganglionic neurons.

• The cell bodies of the preganglionic neurons are located in the intermediolateral column (IML) of the spinal cord and in motor nuclei of some cranial nerves

• preganglionic axons are small-diameter, myelinated, relatively slowly conducting B fibers.

• The axons of the postganglionic neurons are mostly unmyelinated C fibers and terminate on the visceral effectors. 3Copyright : www.rxdentistry.net

Preganglionic and Postganglionic Neurons

• Each autonomic nervous pathway from CNS to innervated organ is a two neuron chain

• The cell body of the first neuron in the series is located in CNS

• Its axon ,preganglionic fiber, synapses with the cell body of 2nd neuron, which lies within a ganglion

• The axon of 2nd neuron, postganglionic fiber, innervates the effector organ


SYMPATHETIC DIVISION OF ANS

• The sympathetic nerve fibers originate in the spinal cord along with spinal nerves between cord segments T-1 and L-2 and pass first into the sympathetic chain and then to the tissues and organs that are stimulated by the sympathetic nerves


Preganglionic and Postganglionic Sympathetic Neurons

• Most sympathetic preganglionic fibers are very short,synapsing with cell bodies of postganglionic neurons within ganglia that lie in a sympathetic ganglion chain located along either side of spinal cord

• Long postganglionic fibers originating in ganglionic chain end on effector organs.some preganglionic fibers pass through ganglion chain without synapsing instead end in sympathetic collateral ganglia


Parasympathetic division

• The parasympathetic nervous system is sometimes called the craniosacral division of the ANS because of the location of its preganglionic neurons

• The parasympathetic nerves supply the visceral structures in the head via the oculomotor, facial, and glossopharyngeal nerves, and those in the thorax and upper abdomen via the vagus nerves

• The sacral outflow supplies the pelvic viscera via branches of the second to fourth sacral spinal nerves.

• Parasympathetic preganglionic fibers synapse on ganglia cells clustered within the walls of visceral organs; thus these parasympathetic postganglionic fibers are very short.


Chemical Transmission at Autonomic Junctions

• Transmission at the synaptic junctions between pre- and postganglionic neurons and between the postganglionic neurons and the autonomic effectors is chemically mediated

• The principal transmitter agents involved are acetylcholine and norepinephrine


Cholinergic transmission

• The neurons that are cholinergic (ie, release acetylcholine) are

• all preganglionic neurons• all parasympathetic postganglionic neurons• sympathetic postganglionic neurons that

innervate sweat glands• sympathetic postganglionic neurons that end

on blood vessels in some skeletal muscles and produce vasodilation when stimulated


Adrenergic transmission

• The adrenal medulla is essentially a sympathetic ganglion in which the postganglionic cells have lost their axons and secrete norepinephrine and epinephrine directly into the bloodstream

• The remaining sympathetic postganglionic neurons are noradrenergic (ie, release norepinephrine).


Synthesis of Acetylcholine, Its Destruction After Secretion, and

Its Duration of Action

• Acetylcholine is synthesized in the terminal endings of the cholinergic nerve fibers stored in vesicles in highly concentrated form until it is released.

• Acetyl-CoA +Choline = Acetylcholine

• Enzyme is cholineacetyl transferase

• After neural transmission it is split into an acetate ion and choline, catalyzed by the enzyme acetylcholinesterase


Synthesis of Norepinephrine

• Synthesis begins in the axoplasm of the terminal adrenergic nerve endings

• Complete inside the secretory vesicles

• Final conversion to Epinephrine in adrenal medulla


Receptors on the Effector Organs

• An acetylcholine, norepinephrine, or epinephrine secreted at an autonomic nerve ending can stimulate effector only by binding to receptor

• The receptor is on the outside of the cell membrane, bound as a prosthetic group to a protein molecule that penetrates all the way through the cell membrane

• Two Principal Types of Acetylcholine Receptors—Muscarinic and Nicotinic Receptors

• Adrenergic Receptors—Alpha and Beta Receptors17Copyright : www.rxdentistry.net

Muscarinic and NicotinicReceptors

• Acetylcholine activates mainly two types of receptors. They are called muscarinic and nicotinic receptors.

• Muscarinic receptors are found on all effector cells that are stimulated by the postganglionic cholinergic neurons of either the parasympathetic nervous system or the sympathetic system

• Nicotinic receptors are found in the autonomic ganglia at the synapses between the preganglionic and postganglionic neurons of both the sympathetic and parasympathetic systems


Adrenergic Receptors—Alpha andBeta Receptors

• There are two major types of adrenergic receptors, alpha receptors and beta receptors.

• There is a division of alpha receptors into alpha1 and alpha2 receptors

• The beta receptors in turn are divided into beta1 and beta2 receptors because certain chemicals affect only certain beta receptors.

• Norepinephrine excites mainly alpha receptors but excites the beta receptors to a lesser extent as well while epinephrine excites both types of receptors approximately equally


The Autonomic Nervous System

Sympathetic stimulation• Iris—pupil dilatation• Salivary glands—stimulation• Heart—rate & force increases• Lungs—bronchial m relaxed• Stomach—peristalisis

decreases • Intestine— motility reduces• Kidney—urine formation

decreases • Bladder—wall relaxed sphincter

closed

Parasympathetic stimulation• Pupil constriction• Inhibition• Rate & force decreases• Contracted • Gastric juice increses

• Motility increses • Urine increases• Wall contracted,sphincter

relaxes21Copyright : www.rxdentistry.net

Alarm or “stress” response of Sympathetic ANS


Control of ANS by higher centers

• Many neuronal areas in the brain stem reticular substance along the course of the tractus solitaries of the medulla, Pons, mesencephalon control autonomic functions

• arterial pressure, heart rate, gastrointestinal secretion, peristalsis and bladder contraction

• Signals from the hypothalamus and even from the cerebrum can affect the activities of almost all the brain stem autonomic control centers


Autonomic reflexes

• Cardiovascular Autonomic Reflexes: baroreceptor reflexes of CVS include baroreceptors which help in regulation of BP

• Gastrointestinal Autonomic Reflexes: The uppermost part of the gastrointestinal tract and the rectum are controlled by autonomic reflexes. Like salivation induced by smell of food


Pharmacology of theAutonomic Nervous System

• Sympathomimetic Drugs: Drugs That Act on Adrenergic Effector Organs

Phenylepherine(alpha receptors), Isoproterenol (beta receptors ) Albuterol (only beta2 receptors).• An indirect sympathomimetic Drugs: Drugs That Cause

Release of Norepinephrine from Nerve Endings Ephedrine Tyramine Amphetamine


ADRENERGIC ANTAGONISTS

• Adrenergic blockers: Drugs That Block Adrenergic Activity.

• Synthesis & storage ofNE –reserpine• Release of norepinephrine from the sympathetic

Endings - guanethidine.• The sympathetic alpha receptors :phenoxybenzamine

and phentolamine • The sympatheticbetareceptors: propranolol,metoprolol • Transmission of nerve impulses through ganglia :

hexamethonium


Parasympathomimetic Drugs (Cholinergic Drugs)

• Drugs That Act on Cholinergic Effector Organs pilocarpine and methacholine. (MUSCRANIC

RECEPTORS)• Anticholinesterase Drugs : Drugs That Have a

Parasympathetic Potentiating Effect These drugs inhibit acetylcholinesterase, thus preventing rapid destruction of the acetylcholine

neostigmine, pyridostigmine, and ambenonium • Antimuscarinic Drugs : Drugs That Block Cholinergic

Activity at Effector Organs -Atropine and similar drugs, such as homatropine and scopolamine


Drugs That Stimulate or BlockSympathetic and Parasympathetic

Postganglionic Neurons

• Drugs That Stimulate Autonomic Postganglionic Neurons: acetylcholine, Nicotine

• Ganglionic Blocking Drugs : drugs block impulse transmission from the autonomic preganglionic neurons to the postganglionic neurons.these r tetraethyl ammonium ion, hexamethonium ion, and pentolinium. 29Copyright : www.rxdentistry.net

PROSTHODONTIC & DENTAL CONSIDERATIONS

• Noxious stimuli can be considered as a stressful event.• The resulting pain sensation affects the activity of the sympathetic nervous system. The sympathetic

activation pattern is characterized by an instantaneous defense behavior.

• As a biochemical correlate to suchstress,Catecholamines are released from the adrenal medulla into the circulation together with other metabolic changes.

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THE SYMPATHETIC NERVOUS SYSTEM IN ACUTEORAL PAIN

• The involvement of the sympathetic system seems to play this role of replacement thus producing sympathetically maintained pain symptoms due to the sprouting of the sympathetic fibers to reach the peripheral nervous system.



THE SYMPATHETIC NERVOUS SYSTEM IN ACUTE ORAL PAIN

• Xerostomia is defined as a subjective complaint of dry mouth that may result from a decrease in the production of saliva.

• Both the parasympathetic and sympathetic nervous systems innervate the salivary glands.

• Parasympathetic stimulation induces more watery secretions, whereas the sympathetic system produces a sparser and more viscous flow. Therefore, a sensation of dryness may occur, for example, during episodes of acute anxiety or stress, which cause changes in salivary composition owing to predominant sympathetic stimulation during such periods.Copyright : www.rxdentistry.net 32


Xerostomia

• Dental-related findings include evidence of an increased tendency to develop cervical caries and denture discomfort accompanied by loss of retention.



Xerostomia

• GAGGING IS A FREQUENT impediment to the performance of dental procedures.This stimulation of the gagging reflex, or more accurately, the vomiting reflex,is a special problem in prosthodontic service.

• The nerve pathways involved in the gagging or vomiting reflex belong mainly to the parasympathetic portion of the autonomic nervous system.



GAGGING

• Lesions of the peripheral nervous system may be associated with syndromes affecting the facial, glossopharyngeal, or vagal nerve, with the facial nerve affected most frequently. In idiopathic CN VII palsy (Bell palsy), gustatory dysfunction can be the predominant and sometimes earliest symptom.


PROSTHODONTIC & DENTAL CONSIDERATIONSGustatory Dysfunction

CONCLUSION


In all these conditions, it seems that the role of

the autonomic nervous system is to try and

restore a balance when the normal circuits of the

nervous system are not sufficient, injured or

destroyed.

BIBLIOGRAPHY

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• CONTRIBUTION OF SYMPATHETIC INNERVATION IN TASTE DYSFUNCTION(LEBANESE MEDICAL JOURNAL 2007 VOL 55(2)

• GANONGS REVIEW OF MEDICAL PHYSIOLOGY 23RD EDITION

• GUYTONS MEDICAL PHYSIOLOGY 11NTH EDITION

• HEARTWELL SYLLABUS OF COMPLETE DENTURES

• NEUROLOGICAL ASPECTS OF TASTE DYSFUNCTION(ARCH NEUROL/VOL 60, MAY 2003)

• MANAGEMENT OF GAGGING PATIENT(J PROSTH DENT JULY AUGUST 1959)

• XEROSTOMIA(JADA, Vol. 134, January 2003)

THANK YOU


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