NEUROPHYSIOLOGY OF NEUROPHYSIOLOGY OF LOCAL ANESTHESIALOCAL ANESTHESIA

DR V.RAMKUMARDR V.RAMKUMARCONSULTANT DENTAL & CONSULTANT DENTAL &

FACIOMAXILLARY SURGEONFACIOMAXILLARY SURGEONREG.NO :4118-TAMILNADU REG.NO :4118-TAMILNADU

INDIA(ASIA)INDIA(ASIA)

LOCAL ANAESTHESIALOCAL ANAESTHESIA

It is defined as loss of sensation in a It is defined as loss of sensation in a cirumscribed area of the cirumscribed area of the bodycaused by depression of bodycaused by depression of excitation ina nerve endingsor an excitation ina nerve endingsor an inhibition of conduction process in inhibition of conduction process in peripheral nervesperipheral nerves

METHODS OF INDUCING LAMETHODS OF INDUCING LA

Mechanical traumaMechanical traumaLow temperatureLow temperatureChemical irritantsChemical irritantsNeurolytic agents such as alcohol Neurolytic agents such as alcohol

&phenol&phenolChemical agents such as local Chemical agents such as local

anestheticsanesthetics

WHAT ARE THE PROPERTIES OF WHAT ARE THE PROPERTIES OF LALA

Non irritatingNon irritatingLess systemic toxicityLess systemic toxicityTime of onset to be shortTime of onset to be short Increaseduration of actionIncreaseduration of actionCompletely reversibleCompletely reversibleNon allergic Non allergic To be stableTo be stable

The messages in the form of electric The messages in the form of electric action porentials are called impulses.action porentials are called impulses.

Resting membrane potential( -70 Resting membrane potential( -70 mv) the interior of the nerve is mv) the interior of the nerve is negative relative to the exterior.negative relative to the exterior.

Depolarization- excitation of nerve Depolarization- excitation of nerve segment increase permiability of na+ segment increase permiability of na+ ions into cell membrane.-50 to-60mvions into cell membrane.-50 to-60mv

Repolarization- inactivating the Repolarization- inactivating the increase in permiability of na+ ions , increase in permiability of na+ ions , there may be incerase in permiability there may be incerase in permiability of k+ ionsof k+ ions

Impulse spread- slow in un Impulse spread- slow in un myelinated nerve fibres myelinated nerve fibres

Myelinated nerve fibres- increase Myelinated nerve fibres- increase spread due to myelination and spread due to myelination and insulating material , impulse insulating material , impulse conduction occurs by means of leap conduction occurs by means of leap from node to node by process called from node to node by process called saltatory conduction saltatory conduction

Impulse propogation- impulse moves Impulse propogation- impulse moves along the surface of axon by energy along the surface of axon by energy derived from nerve membranederived from nerve membrane

Mode And Site Of Action Of LaMode And Site Of Action Of La

Altering the basic resting potential of Altering the basic resting potential of nerve membranenerve membrane

Altering the treshold potentialAltering the treshold potentialDecreasing the rate of depoalrizationDecreasing the rate of depoalrizationProlong the rate of depolarizationProlong the rate of depolarization

HOW DO THE LA WORKHOW DO THE LA WORKVARIOUS THEORY OF LAVARIOUS THEORY OF LA

Acetyl choline theoryAcetyl choline theoryCalcium displacement theoryCalcium displacement theorySurface charge theorySurface charge theoryMembrane expansion theoryMembrane expansion theorySpecific receptor theorySpecific receptor theory

Acetyl choline theory- it mainly acts Acetyl choline theory- it mainly acts on the neuro transmitteron the neuro transmitter

Calcium displacement theory-Calcium displacement theory-diplacement of calcium ion from cell diplacement of calcium ion from cell membrane ,controlled permiability of membrane ,controlled permiability of sodium ionsodium ion

Surface charge theory- changing the Surface charge theory- changing the electrical potential at th enerve electrical potential at th enerve membrane, binding the nerve membrane, binding the nerve membrane to la moleculesmembrane to la molecules

Membrane expansion theory- la Membrane expansion theory- la binds to the hdrophobic region binds to the hdrophobic region increase in bulk structure by increase in bulk structure by expansion of the membraneexpansion of the membrane

Specific receptor theory- la binding Specific receptor theory- la binding to specific receptor to sodium to specific receptor to sodium channel channel

CLASSIFICATION OF LOCAL CLASSIFICATION OF LOCAL ANESTHETIC SUBSTANCE ANESTHETIC SUBSTANCE

ACCORDING TO THE BIOLOGIC ACCORDING TO THE BIOLOGIC SITE AND MODE OF ACTION SITE AND MODE OF ACTION

definition chemical definition chemical substancesubstance

Class A Receptor on - BiotoxinsClass A Receptor on - Biotoxinsxternal surface of nerve membranexternal surface of nerve membrane classB- Receptor on internal -Quartenary classB- Receptor on internal -Quartenary surface of nerve membrane ammoniunsurface of nerve membrane ammoniun classC-receptor independent - Benzocaine classC-receptor independent - Benzocaine physiochemicalmecahnismphysiochemicalmecahnism classD – combination of receptor - LAclassD – combination of receptor - LA&receptor –independent mechanism&receptor –independent mechanism

HOW DOES LA WORKHOW DOES LA WORK

Displacement of calcium ions from sodium Displacement of calcium ions from sodium channel receptor sitechannel receptor site

Binding of la molecule to the receptor siteBinding of la molecule to the receptor site Blockade of sodium channelBlockade of sodium channel Decrease in sodium conductanceDecrease in sodium conductance Depression of rate of electrical Depression of rate of electrical

depolarizationdepolarization Failure to achieve the threshold potential Failure to achieve the threshold potential

levellevel Lack of development of propagated action Lack of development of propagated action

potential levelpotential level Conduction blockadeConduction blockade

Nerve block produced by local anesthetics is Nerve block produced by local anesthetics is called non depolarizing nerve block because called non depolarizing nerve block because the nerve is unable to relaese energythe nerve is unable to relaese energy

Diffusion- the movement of LA from extra Diffusion- the movement of LA from extra cellular neural deposition site towards the cellular neural deposition site towards the nervenerve

Mantle bundles- fasiculi located near the Mantle bundles- fasiculi located near the surface of the nerve they are the first one surface of the nerve they are the first one reached by LA due to increase concentrationreached by LA due to increase concentration

Core bundles fasiculi- located closer to the Core bundles fasiculi- located closer to the centre of the nerve their action is decreasecentre of the nerve their action is decrease

Blocking process- some of the LA are Blocking process- some of the LA are absorbed by nerve through diffusionabsorbed by nerve through diffusion

Induction time- is defined as the Induction time- is defined as the period from deposition of the period from deposition of the anesthetic solution of complete anesthetic solution of complete conduction blockadeconduction blockade

Vasoactivity- increase in injection of Vasoactivity- increase in injection of LA into the blood vessel causes vaso LA into the blood vessel causes vaso dilatationdilatation

Factors affecting local anesthetic Factors affecting local anesthetic actionaction

Factor Action affected DescriptionFactor Action affected Description Pka onset lower pka Pka onset lower pka

increaseincrease action onsetaction onset Lipid solubility Anesthetic potency increased Lipid solubility Anesthetic potency increased

lipid lipid solubility increased solubility increased

potency potency Protein binding Duration increase Protein binding Duration increase

protein protein binding binding increase increase duration of action duration of action

Factor Action affected Description Factor Action affected Description Non nervous onset increased Non nervous onset increased

diffusibility diffusibility

tissue diffusibility tissue diffusibility

Vaso dilator activity anesthetic potency Greater Vaso dilator activity anesthetic potency Greater

Duration vasodilator Duration vasodilator activityactivity