Electrical Stimulation of Nerves & Pain Gate Theories DPT-V

Lecture#03_____ DPT-VDr.FOUZIA BATOOLPT.PP-DPTLecturer, RCRSElectrical Stimulation of NervesPain Assessment ScalesPain Gate Theories

Lecture Contents Electrical Stimulation of Nerves Normal physiology of nerves:Difference in potential between the inside and outside of a nerveDifference in concentration of ions inside and outside the plasma membranes

Electrical stimulation of nervesPolarized stage of the membraneResting nerve is positive outside and negative insidePlasma membrane is not permeable to sodium ions

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7OUTSIDEINSIDEK+ = Potassium; Na+ = Sodium; Cl- = Chloride; Pr- = proteinsNa+Na+K+K+Force of DiffusionElectrostatic Force+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - Cl-Force of DiffusionCl-Electrostatic ForcePr-Closedchannelopenchannelopenchannelnochannel3Na/2KpumpResting Membrane Potential- 65 mV7Charged particles are called ions. Negatively charged ones are anions, while positive ones are cations. Proteins are negatively charged particles and they remain inside the cellStimulation of nerve by the stimulusFall in the potential differenceAlteration in the permeability of the membrane to sodium ionsAlteration in the concentration of ions inside and outside the nerve membraneReversal of polarityNerve stimulation

Phase 0Stable resting potentialWhen a stimulus above the threshold potential strikes the cell the cell begins to depolarize. Sodium ions rush into the cell causing the electrochemical difference potential between the inside and outside of the cell to race toward zeroPhase 1 The depolarization phaseThe electrochemical voltage change is so rapid that the voltage overshoots the zero potential and tops out around+20mVPhases of Membrane potentialPhase 2Plateau phaseThe trans-membrane action potential is maintained near 0mV by the infusion ofcalcium ions. At the end of this phase, the cell begins to repolarize.Phase 3Rapid repolarization phaseThe cell restores itself to the original polarized state of -70mVContInitiated by Electrical StimulusA varying current of adequate intensity must be appliedPD is set up across it as the current flowsIf the PD falls below the level at which the membrane become permeable to sodium ions, these ions begin to enter the axon and initiates the series of events for initiation of nerve impulse Electrical stimulation of the nervesAdaptation of nerve due to constant flow of currentUnvarying current is not effective in initiating an impulseAccommodationSensory nerve is stimulated the downward traveling impulse has no effect, but upward traveling impulse is appreciated when it reaches brain Sensory stimulation experienced varies with the duration of the impulse Long duration produce an uncomfortable, stabbing sensationLess duration produces less uncomfortable, stabbing sensationImpulses of 1ms and less produces a mild prickling sensation Sensory nerveThe upward traveling impulse is unable to pass the first synapse, as it is traveling in the wrong direction, but the downward-traveling impulse to the muscles supplied by the nerves, causing them to contractStimulus applied to a motor trunk, impulses pass to all the muscles that the nerve supplies below the point at which it is stimulated, causing them to contract Motor nerveSingle stimulus____ simultaneously to a number of motor units resulting in brisk contraction, followed by immediate relaxation

If one stimulus is applied per second, each produces an isolated contraction and there is time for complete relaxation between the impulses Effects of frequency of stimulationIncrease frequency shortens the periods of relaxationFrequency more than 20Hz there is no time for complete relaxation between the contraction_____ resulting in partial tetanyFrequency more than 60Hz there is no perceptible relaxation ____resulting in full tetany

ContFactors influences:Number of motor units activatedIntensity of current appliedRate of change of currentIf intensity of current suddenly rises there is no time for accommodation to take place and a muscle contraction resultsStrength of ContractionIf the current rises more slowly, there is some accommodation and a greater intensity is needed to produce a contractionContPain Assessment scale PAIN CONTROL THEORIESPAIN RATING SCALEAn unpleasant sensory & emotional experience associated with actual or potential tissue damage, or described in terms of such damage The International Association for the Study of Pain

Physiological response produced by activation of specific types of nerve fibersExperienced because of nociceptors being sensitive to extreme mechanical, thermal, & chemical energy. Behavioral indicators of pain are crying, mood changes and from facial expression.One of the bodys defense mechanismAcute vs. Chronic What is Pain?Visual & Numeric Analogue Scales None Severe 0 10Locate area of pain on a picturesMcGill pain questionnaireEvaluate sensory, evaluative, & affective components of pain20 subcategories, 78 wordsPain Assessment Scales

Does not interfere with most activitiesAble to adapt to pain psychologically and with medication or devices such as cushions0 No painFeeling perfectly normal1 (Very Mild):Very light barely noticable pain2 (Discomforting) Minor pain, like lightly pinching the fold of skin between the thumb and first finger with the other hand, using the fingernails3 (Tolerable):Very noticable pain, like an accidental cut, a blow to the nose causing a bloody nose, or a doctor giving you an injection

Minor 0,1,2,3:

Interferes with many activities, Interferes with many activitiesRequires lifestyle changes but patient remains independent4 DistressingStrong, deep pain, like an average toothache, the initial pain from a bee sting, or minor trauma to part of the body, such as stubbing your toe real hard5 Very DistressingStrong, deep, piercing pain, such as a sprained ankle when you stand on it wrong, or mild back pain6 IntenseAt this point you begin to have trouble holding a job or maintaining normal social relationshipsModerate Pain 4, 5, 6Unable to engage in normal activitiesPatient is disabled and unable to function independently7 Very IntenseThe pain completely dominates your senses, causing you to think unclearly about half the time8 Utterly HorriblePain so intense you can no longer think clearly at all, and have often undergone severe personality change if the pain has been present for a long time

Severe Pain 7, 8, 9, 109 ExcruciatingUnbearablePain so intense you cannot tolerate it and demand pain killers or surgery, no matter what the side effects or risk10 ExcruciatingThose who have suffered a severe accident, such as a crushed hand, and lost consciousness as a result of the pain and not blood loss, have experienced level 10.Pain so intense you will go unconscious shortly

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Where Does Pain Come From?Cutaneous Pain sharp, bright, burning; can have a fast or slow onset

Deep Somatic Pain from tendons, muscles, joints, periosteum, & blood vessels

Visceral Pain originates from internal organs; diffused at 1st & later may be localized (i.e. appendicitis)

Psychogenic Pain individual feels pain but cause is emotional rather than physicalPain SourcesFast vs. Slow Pain Fast localized; carried through A-delta axons in skinSlow aching, throbbing, burning; carried by C fibersNociceptive neuron transmits pain info to spinal cord via unmyelinated C fibers & myelinated A-delta fibers.The smaller C fibers carry impulses @ rate of 15 pulses/sec.The larger A-delta fibers carry impulses @ rate of 40 pulses/sec.

Transmission of PainTypes of NervesNeurotransmitters: Chemical substances that allow nerve impulses to move from one neuron to anotherFound in synapsesSubstance P - thought to be responsible for the transmission of pain-producing impulses

Types of NervesAfferent (Ascending) transmit impulses from the periphery to the brainFirst Order neuronSecond Order neuronThird Order neuronEfferent (Descending) transmit impulses from the brain to the periphery

First Order NeuronsStimulated by sensory receptorsEnd in the dorsal horn of the spinal cordTypesA-alpha non-pain impulsesA-beta non-pain impulsesLarge, myelinatedLow threshold mechanoreceptor; respond to light touch & low-intensity mechanical responseA-delta pain impulses due to mechanical pressure Large diameter, thinly myelinatedShort duration, sharp, fast, bright, localized sensation (prickling, stinging, burning)C pain impulses due to chemicals or mechanical Small diameter, unmyelinatedDelayed onset, diffuse nagging sensation (aching, throbbing)

Second Order NeuronsReceive impulses from the FON in the the dorsal hornLamina II, Substantia Gelatinosa (SG) - determines the input sent to T cells from peripheral nerveT Cells (transmission cells): transmission cell that connects sensory n. to CNS; neurons that organize stimulus input & transmit stimulus to the brainTravel along the spinothalmic tract Pass through Reticular FormationEnds in thalamusTypesWide range specificReceive impulses from A-beta, A-delta, & CNociceptive specificReceive impulses from A-delta & CThird Order NeuronsBegins in thalamusEnds in specific brain centers (cerebral cortex)Perceive location, quality, intensityAllows to feel pain, integrate past experiences & emotions and determine reaction to stimulusSynapses

Descending NeuronsDescending Pain Modulation (Descending Pain Control Mechanism)Transmit impulses from the brain (corticospinal tract in the cortex) to the spinal cord (lamina)Periaquaductal Gray Area (PGA) release EnkephalinsNucleus Raphe Magnus (NRM) release SerotoninThe release of these neurotransmitters inhibit ascending neuronsStimulation of the PGA in the midbrain & NRM in the pons & medulla causes analgesia.Endogenous opioid peptides - Endorphins & Enkephalins

Sensory ReceptorsMechanoreceptors touch, light or deep pressureMeissners corpuscles (light touch), Pacinian corpuscles (deep pressure), Merkels corpuscles (deep pressure)Thermoreceptors - heat, coldRuffini corpuscles (in the skin) touch, tension, heat; (in joint capsules & ligaments change of position)Proprioceptors change in length or tensionMuscle Spindles, Golgi Tendon OrgansNociceptors painful stimuli MechanosensitiveChemosensitiveNociceptorsSensitive to repeated or prolonged stimulationMechanosensitive excited by stress & tissue damageChemosensitive excited by the release of chemical mediatorsBradykinin, Histamine, Prostaglandins, Arachadonic Acid

Pain Control TheoriesGate Control TheoryCentral Biasing TheoryEndogenous Opiates TheoryGate Control TheoryMelzack & Wall, 1965Substantia Gelatinosa (SG) in dorsal horn of spinal cord acts as a gate only allows one type of impulses to connect with the SONTransmission Cell (T-cell) distal end of the SON

If A-beta neurons are stimulated SG is activated which closes the gate to A-delta & C neuronsIf A-delta & C neurons are stimulated SG is blocked which closes the gate to A-beta neuronsGate Control TheoryGate - located in the dorsal horn of the spinal cordSmaller, slower n. carry pain impulsesLarger, faster n. fibers carry other sensations

BrainPainHeat, Cold, MechanicalGate (T cells/ SG)Central Biasing TheoryDescending neurons are activated by: stimulation of A-delta & C neurons, cognitive processes, anxiety, depression, previous experiences, expectationsCause release of enkephalins (PAG) and serotonin (NRM)Enkephalin interneuron in area of the SG blocks A-delta & C neuronsEndogenous Opiates TheoryLeast understood of all the theoriesStimulation of A-delta & C fibers causes release of B-endorphins from the PAG & NRMOrACTH/B-lipotropin is released from the anterior pituitary in response to pain broken down into B-endorphins and corticosteroids

Mechanism of action similar to enkephalins to block ascending nerve impulses

Examples: TENS (low freq. & long pulse duration)Claytons ElectrotherapyElectrotherapy by Muhammad Salabat KhanReferences