Introduction to Oral Introduction to Oral PhysiologyPhysiology

Physiology of PainPhysiology of Pain

Oral PhysiologyOral Physiology

Dent 207Dent 207

Physiology & oral physiologyPhysiology & oral physiology

A branch of biology that deals with the study A branch of biology that deals with the study of functions of living matterof functions of living matter

Oral physiology is the study of the functions of Oral physiology is the study of the functions of the mouth and associated structuresthe mouth and associated structures

Functions of the human mouthFunctions of the human mouth

The portal to GITThe portal to GIT Guiding food intakeGuiding food intake Preparing food for swallowing and digestionPreparing food for swallowing and digestion

Speech productionSpeech production Human traitHuman trait Requires complicated control of many oral, Requires complicated control of many oral,

pharyngeal and laryngeal structurespharyngeal and laryngeal structures Prehensile (holding objects)Prehensile (holding objects)

More evident in animalsMore evident in animals

Functions of oral cavity are Functions of oral cavity are organizedorganized

Food analyzed by sensory systems involved in perception ofFood analyzed by sensory systems involved in perception of TasteTaste SmellSmell TouchTouch TemperatureTemperature PainPain

Sensory information is integrated in the brain, as a resultSensory information is integrated in the brain, as a result Saliva is secretedSaliva is secreted

LubricationLubrication Calcification - calculusCalcification - calculus

Chewing movements beginChewing movements begin Mastication - occlusionMastication - occlusion Neuromuscular control of muscle movementsNeuromuscular control of muscle movements Protection from tissue damageProtection from tissue damage

Swallowing eventually occursSwallowing eventually occurs

Why study oral physiologyWhy study oral physiology

Knowledge of normal functions of the mouth Knowledge of normal functions of the mouth leads toleads to

Explanation of orofacial dysfunction, thereforeExplanation of orofacial dysfunction, therefore Suggesting better methods for diagnosis & Suggesting better methods for diagnosis &

treatmenttreatment Practical example of how knowledge of oral Practical example of how knowledge of oral

physiology has an impact on industry & physiology has an impact on industry & marketingmarketing Fooling taste system by diet sweetsFooling taste system by diet sweets

PainPain

Dentistry owes its very beginning to the quest Dentistry owes its very beginning to the quest for pain relieffor pain relief

Classical foundations of dental professionClassical foundations of dental profession IdentificationIdentification DiagnosisDiagnosis Elimination of painElimination of pain

PainPain

A subjective symptomA subjective symptom A reaction elicited by a stimulusA reaction elicited by a stimulus May involve a tissue damageMay involve a tissue damage Provides a warning to seek treatmentProvides a warning to seek treatment Acute vs chronicAcute vs chronic Spontaneous vs. provokedSpontaneous vs. provoked Continuous vs. intermittentContinuous vs. intermittent Recurrent – periodicRecurrent – periodic Localized – spreading – migrating - referredLocalized – spreading – migrating - referred

PainPain

DefinitionDefinition A complex series of phenomenaA complex series of phenomena Unpleasant emotional & Unpleasant emotional &

sensory experiences associated sensory experiences associated with actual or potential tissue with actual or potential tissue damage damage

Abnormal affective state Abnormal affective state aroused by the pathological aroused by the pathological activity of a specific sensory activity of a specific sensory systemsystem

PainPain Pain is not simply an excessive stimulation of some other Pain is not simply an excessive stimulation of some other

sense such as touch or temperaturesense such as touch or temperature But instead is related to tissue damage at a cellular levelBut instead is related to tissue damage at a cellular level This is why physiologists replace “pain” with “noxious” & This is why physiologists replace “pain” with “noxious” &

pain receptors with “nociceptors”pain receptors with “nociceptors” Pain stimulants – products of tissue damagePain stimulants – products of tissue damage

Hydrogen ionsHydrogen ions Potassium ionsPotassium ions ProstaglandinsProstaglandins PolypeptidesPolypeptides HistamineHistamine SerotoninSerotonin

Aspirin blocks the chemical receptorsAspirin blocks the chemical receptors

NociceptorsNociceptors Touch & temperature receptors are well definedTouch & temperature receptors are well defined Pain receptors (nociceptors) respond to painful stimuliPain receptors (nociceptors) respond to painful stimuli ““Nociceptor” is a term used to describe a nerve ending that Nociceptor” is a term used to describe a nerve ending that

responds to stimuli that actually or potentially produce tissue responds to stimuli that actually or potentially produce tissue damagedamage

Nociceptors may respond to very gross mechanical stimuliNociceptors may respond to very gross mechanical stimuli Other stimuli may result in painful sensation when level of Other stimuli may result in painful sensation when level of

stimulus is increasedstimulus is increased A single noxious heat stimulus is sensed as painfulA single noxious heat stimulus is sensed as painful Repetitive stimulation of temperature receptors with less Repetitive stimulation of temperature receptors with less

powerful stimuli may inhibit the passage of painpowerful stimuli may inhibit the passage of pain

AAδδ or C fibers or C fibers

Information originating in nociceptors travels Information originating in nociceptors travels over small diameter afferent nerves (Aover small diameter afferent nerves (Aδδ or C or C fibers group)fibers group)

Double nature of painDouble nature of pain AAδδ – faster – producing stinging pain (sharp of – faster – producing stinging pain (sharp of

high intensity – initial pain)high intensity – initial pain) C – slower - producing agonizing intolerable - C – slower - producing agonizing intolerable -

diffuse second paindiffuse second pain

AAδδ fibers fibers

Myelinated (2.5 µm)Myelinated (2.5 µm) Conducting at 12-30 m/sConducting at 12-30 m/s High thresholdHigh threshold Transmit information from nociceptors or Transmit information from nociceptors or

mechanoreceptorsmechanoreceptors Activated by intense mechanical stimulationActivated by intense mechanical stimulation Involved with 1Involved with 1stst pain pain

Sharp localized sensation from obvious Sharp localized sensation from obvious mechanical damagemechanical damage

C fibersC fibers

Non-myelinated (0.4-1.2 µm)Non-myelinated (0.4-1.2 µm) Conducting at 0.5-2 m/sConducting at 0.5-2 m/s PolymodalPolymodal

Transmit a number of different stimuli though they are Transmit a number of different stimuli though they are thought to be purely nociceptive in humanthought to be purely nociceptive in human

Excited by intense mechanical, thermal & chemicalExcited by intense mechanical, thermal & chemical Involved with 2Involved with 2ndnd pain pain

Diffuse & dull that follows 1Diffuse & dull that follows 1stst pain pain May arise independentlyMay arise independently

Pain neuronPain neuron

NeuronNeuron Cell body and dendritic processesCell body and dendritic processes AxonAxon

Neurons conducting painNeurons conducting pain PrimaryPrimary SecondarySecondary TertiaryTertiary

Pain neuronPain neuron Primary neuronPrimary neuron

Cell bodies inCell bodies in Posterior root ganglia of spinal cordPosterior root ganglia of spinal cord Ganglia of cranial nervesGanglia of cranial nerves

In the cranial area; all primary In the cranial area; all primary neurons conduct pain from pain neurons conduct pain from pain receptor nerve endings to the receptor nerve endings to the Spinal Nucleus of Trigeminal Spinal Nucleus of Trigeminal nerve nerve irrespective of the cranial irrespective of the cranial nerve of originnerve of origin

Secondary neuronSecondary neuron From SN-CN5 to thalamusFrom SN-CN5 to thalamus

Tertiary neuronTertiary neuron Thalamus to cerebral cortexThalamus to cerebral cortex

Gate control theoryGate control theory

Stimulation of other sensory receptors at the Stimulation of other sensory receptors at the same time as the nociceptors can prevent the same time as the nociceptors can prevent the perception of pain – gate control theoryperception of pain – gate control theory

If the impulses in the nociceptive nerves could If the impulses in the nociceptive nerves could proceed up to the cortex, pain would be proceed up to the cortex, pain would be perceived – the “pain gate” would be openedperceived – the “pain gate” would be opened

Explains why pressing on a painful area or Explains why pressing on a painful area or clenching on a painful tooth relieves the painclenching on a painful tooth relieves the pain

Can explain acupuncture treatmentCan explain acupuncture treatment

Indigenous Morphine-like Indigenous Morphine-like substancessubstances

Self readingSelf reading Oral Bioscience, chapter 11: Oral sensationOral Bioscience, chapter 11: Oral sensation

Page 232 -233Page 232 -233

Factors affecting pain thresholdFactors affecting pain threshold

Lowering thresholdLowering threshold Psychological factorsPsychological factors Fear & worryFear & worry

Elevating thresholdElevating threshold Excitement & relaxationExcitement & relaxation Soothing musicSoothing music

Nerve PhysiologyNerve Physiology

The conduction of a The conduction of a nerve impulsenerve impulse

Nerve cell axonNerve cell axon Intracellular FluidIntracellular Fluid Extracellular FluidExtracellular Fluid Na and K ionsNa and K ions Na and K channelsNa and K channels Difference in polarity of Difference in polarity of

interior and exterior of interior and exterior of axonaxon

Nerve PhysiologyNerve Physiology

Resting Membrane PotentialResting Membrane Potential A result of the relative distribution of Na and K ions across A result of the relative distribution of Na and K ions across

the axon membranethe axon membrane IntracellularlyIntracellularly

[K[K++] is high, [Na] is high, [Na++] is low] is low ExtracellularlyExtracellularly

[Na[Na++] is high, [K] is high, [K++] is low] is low At the state of restAt the state of rest

The interior of the axon is -ve relative to the exteriorThe interior of the axon is -ve relative to the exterior Potential difference of about 60 - 90 mVPotential difference of about 60 - 90 mV The natural tendency of Na influx is prevented by Na pump, a The natural tendency of Na influx is prevented by Na pump, a

process that needs energyprocess that needs energy

DepolarisationDepolarisation

Action Potential and DepolarisationAction Potential and Depolarisation Rapid fall in membrane potential from – 70 to Rapid fall in membrane potential from – 70 to

+20-30 mV+20-30 mV Nerve impulse (action potential) propagates along Nerve impulse (action potential) propagates along

the axon and when it reaches the resting segment the axon and when it reaches the resting segment of the axon it creates an electrical stimulus which of the axon it creates an electrical stimulus which increases the permeability of the diffusion barrier increases the permeability of the diffusion barrier to Na and K ions by opening voltage gated ion to Na and K ions by opening voltage gated ion channelschannels

DepolarizationDepolarization

Na+ ions move into cell while K+ ions move out Na+ ions move into cell while K+ ions move out along concentration gradientalong concentration gradient

Intracellular charge is +ve relative to extracellularIntracellular charge is +ve relative to extracellular This segment of the axon has undergone This segment of the axon has undergone

depolarisationdepolarisation and is in a state of and is in a state of action potentialaction potential As depolarisation progresses along the axon the As depolarisation progresses along the axon the

action potential is propagated and the nerve action potential is propagated and the nerve stimulus continues down the length of the axonstimulus continues down the length of the axon

RepolarisationRepolarisation

The axon returns to its original state with The axon returns to its original state with initial concentrations of Na and K ions initial concentrations of Na and K ions restored and the interior once again -ve restored and the interior once again -ve relative to the exteriorrelative to the exterior

This is achieved by the Na and K channelsThis is achieved by the Na and K channels The axon is ready to undergo depolarisation The axon is ready to undergo depolarisation

again to propagate a nerve impulseagain to propagate a nerve impulse Active process that takes up energyActive process that takes up energy

Mechanism of action of local anesthesiaMechanism of action of local anesthesia

Blocking of the Na ion pumps in the cell membrane Blocking of the Na ion pumps in the cell membrane wallwall

This results in an inability for Na ions influx when the This results in an inability for Na ions influx when the action potential arrives at a given segment of the nerveaction potential arrives at a given segment of the nerve

No effect on resting potentialNo effect on resting potential