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Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
Neurophysiology
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Neurophysiology

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  1. Nervous SystemNervous System NeurophysiologyNeurophysiology
  2.  Neurons are highly irritableNeurons are highly irritable  Action potentials, or nerve impulses,Action potentials, or nerve impulses, are:are:  Electrical impulses carried along the lengthElectrical impulses carried along the length of axonsof axons  Always the same regardless of stimulusAlways the same regardless of stimulus  The underlying functional feature of theThe underlying functional feature of the nervous systemnervous system NeurophysiologyNeurophysiology
  3.  Voltage (V) – measure of potential energyVoltage (V) – measure of potential energy generated by separated chargegenerated by separated charge  Potential difference – voltage measuredPotential difference – voltage measured between two pointsbetween two points  Current (I) – the flow of electrical chargeCurrent (I) – the flow of electrical charge between two pointsbetween two points  Resistance (R) – hindrance to charge flowResistance (R) – hindrance to charge flow  Insulator – substance with high electricalInsulator – substance with high electrical resistanceresistance  Conductor – substance with low electricalConductor – substance with low electrical resistanceresistance Electricity DefinitionsElectricity Definitions
  4.  Reflects the flow of ions rather thanReflects the flow of ions rather than electronselectrons  There is a potential on either side ofThere is a potential on either side of membranes when:membranes when:  The number of ions is different across theThe number of ions is different across the membranemembrane  The membrane provides a resistance to ionThe membrane provides a resistance to ion flowflow Electrical Current and theElectrical Current and the BodyBody
  5.  Types of plasma membrane ion channels:Types of plasma membrane ion channels:  Passive, or leakage, channels – always openPassive, or leakage, channels – always open  Chemically gated channels – open withChemically gated channels – open with binding of a specific neurotransmitterbinding of a specific neurotransmitter  Voltage-gated channels – open and close inVoltage-gated channels – open and close in response to membrane potentialresponse to membrane potential  Mechanically gated channels – open andMechanically gated channels – open and close in response to physical deformationclose in response to physical deformation of receptorsof receptors Role of Ion ChannelsRole of Ion Channels
  6.  Example: NaExample: Na++ -K-K++ gated channelgated channel  Closed when a neurotransmitter is notClosed when a neurotransmitter is not bound to the extracellular receptorbound to the extracellular receptor  NaNa++ cannot enter the cell and Kcannot enter the cell and K++ cannot exitcannot exit the cellthe cell  Open when a neurotransmitter isOpen when a neurotransmitter is attached to the receptorattached to the receptor  NaNa++ enters the cell and Kenters the cell and K++ exits the cellexits the cell Operation of a GatedOperation of a Gated ChannelChannel
  7. Operation of a Gated ChannelOperation of a Gated Channel Figure 11.6a
  8.  Example: NaExample: Na++ channelchannel  Closed when the intracellularClosed when the intracellular environment is negativeenvironment is negative  NaNa++ cannot enter the cellcannot enter the cell  Open when the intracellular environmentOpen when the intracellular environment is positiveis positive  NaNa++ can enter the cellcan enter the cell Operation of a Voltage-Operation of a Voltage- Gated ChannelGated Channel
  9. Operation of a Voltage-Operation of a Voltage- Gated ChannelGated Channel Figure 11.6b
  10.  When gated channels are open:When gated channels are open:  Ions move quickly across the membraneIons move quickly across the membrane  Movement is along their electrochemicalMovement is along their electrochemical gradientsgradients  An electrical current is createdAn electrical current is created  Voltage changes across the membraneVoltage changes across the membrane Gated ChannelsGated Channels
  11.  Ions flow along their chemical gradient whenIons flow along their chemical gradient when they move from an area of high concentrationthey move from an area of high concentration to an area of low concentrationto an area of low concentration  Ions flow along their electrical gradient whenIons flow along their electrical gradient when they move toward an area of opposite chargethey move toward an area of opposite charge  Electrochemical gradient – the electrical andElectrochemical gradient – the electrical and chemical gradients taken togetherchemical gradients taken together Electrochemical GradientElectrochemical Gradient
  12.  The potential difference (–70 mV) across theThe potential difference (–70 mV) across the membrane of a resting neuronmembrane of a resting neuron  It is generated by different concentrationsIt is generated by different concentrations of Naof Na++ , K, K++ , Cl, Cl−− , and protein anions (A, and protein anions (A−− ))  Ionic differences are the consequence of:Ionic differences are the consequence of:  Differential permeability of the neurilemma to NaDifferential permeability of the neurilemma to Na++ and Kand K++  Operation of the sodium-potassium pumpOperation of the sodium-potassium pump Resting Membrane Potential (VResting Membrane Potential (Vrr))
  13. Resting Membrane PotentialResting Membrane Potential (V(Vrr)) Figure 11.8
  14.  Used to integrate, send, and receiveUsed to integrate, send, and receive informationinformation  Membrane potential changes areMembrane potential changes are produced by:produced by:  Changes in membrane permeability to ionsChanges in membrane permeability to ions  Alterations of ion concentrations acrossAlterations of ion concentrations across the membranethe membrane  Types of signals – graded potentials andTypes of signals – graded potentials and action potentialsaction potentials Membrane Potentials: SignalsMembrane Potentials: Signals
  15.  Changes are caused by three eventsChanges are caused by three events  Depolarization – the inside of theDepolarization – the inside of the membrane becomes less negativemembrane becomes less negative  Repolarization – the membrane returns toRepolarization – the membrane returns to its resting membrane potentialits resting membrane potential  Hyperpolarization – the inside of theHyperpolarization – the inside of the membrane becomes more negative than themembrane becomes more negative than the resting potentialresting potential Changes in MembraneChanges in Membrane PotentialPotential
  16. Changes in Membrane PotentialChanges in Membrane Potential Figure 11.9
  17.  Short-lived, local changes in membraneShort-lived, local changes in membrane potentialpotential  Decrease in intensity with distanceDecrease in intensity with distance  Their magnitude varies directly with theTheir magnitude varies directly with the strength of the stimulusstrength of the stimulus  Sufficiently strong graded potentialsSufficiently strong graded potentials can initiate action potentialscan initiate action potentials Graded PotentialsGraded Potentials
  18. Graded PotentialsGraded Potentials Figure 11.10
  19. Graded PotentialsGraded Potentials  Voltage changes in graded potentialsVoltage changes in graded potentials are decrementalare decremental  Current is quickly dissipated due to theCurrent is quickly dissipated due to the leaky plasma membraneleaky plasma membrane  Can only travel over short distancesCan only travel over short distances
  20. Graded PotentialsGraded Potentials Figure 11.11
  21.  A brief reversal of membrane potential with aA brief reversal of membrane potential with a total amplitude of 100 mVtotal amplitude of 100 mV  Action potentials are only generated byAction potentials are only generated by muscle cells and neuronsmuscle cells and neurons  They do not decrease in strength overThey do not decrease in strength over distancedistance  They are the principal means of neuralThey are the principal means of neural communicationcommunication  An action potential in the axon of a neuron isAn action potential in the axon of a neuron is a nerve impulsea nerve impulse Action Potentials (APs)Action Potentials (APs)
  22.  NaNa++ and Kand K++ channels are closedchannels are closed  Leakage accounts for small movements of NaLeakage accounts for small movements of Na++ and Kand K++  Each NaEach Na++ channel has two voltage-regulatedchannel has two voltage-regulated gatesgates  Activation gates –Activation gates – closed in the restingclosed in the resting statestate  Inactivation gates –Inactivation gates – open in the restingopen in the resting statestate Action Potential: Resting StateAction Potential: Resting State Figure 11.12.1
  23.  NaNa++ permeability increases; membranepermeability increases; membrane potential reversespotential reverses  NaNa++ gates are opened; Kgates are opened; K++ gates are closedgates are closed  Threshold – a critical level of depolarizationThreshold – a critical level of depolarization (-55 to -50 mV)(-55 to -50 mV)  At threshold,At threshold, depolarizationdepolarization becomesbecomes self-generatingself-generating Action Potential: DepolarizationAction Potential: Depolarization PhasePhase Figure 11.12.2
  24.  Sodium inactivation gates closeSodium inactivation gates close  Membrane permeability to NaMembrane permeability to Na++ declines todeclines to resting levelsresting levels  As sodium gates close, voltage-sensitive KAs sodium gates close, voltage-sensitive K++ gates opengates open  KK++ exits the cell andexits the cell and internal negativityinternal negativity of the resting neuronof the resting neuron is restoredis restored Action Potential: RepolarizationAction Potential: Repolarization PhasePhase Figure 11.12.3
  25. Action Potential: HyperpolarizationAction Potential: Hyperpolarization  Potassium gates remain open, causing anPotassium gates remain open, causing an excessive efflux of Kexcessive efflux of K++  This efflux causes hyperpolarization of theThis efflux causes hyperpolarization of the membrane (undershoot)membrane (undershoot)  The neuron isThe neuron is insensitive toinsensitive to stimulus andstimulus and depolarizationdepolarization during this timeduring this time Figure 11.12.4
  26.  RepolarizationRepolarization  Restores the resting electrical conditionsRestores the resting electrical conditions of the neuronof the neuron  Does not restore the resting ionicDoes not restore the resting ionic conditionsconditions  Ionic redistribution back to restingIonic redistribution back to resting conditions is restored by the sodium-conditions is restored by the sodium- potassium pumppotassium pump Action Potential:Action Potential: Role of the Sodium-Potassium PumpRole of the Sodium-Potassium Pump
  27. Phases of the Action PotentialPhases of the Action Potential  11 – resting state– resting state  2 – depolarization2 – depolarization  3 – repolarization3 – repolarization  4 –4 – hyperpolarizationhyperpolarization
  28.  NaNa++ influx causes a patch of the axonalinflux causes a patch of the axonal membrane to depolarizemembrane to depolarize  Positive ions in the axoplasm movePositive ions in the axoplasm move toward the polarized (negative) portiontoward the polarized (negative) portion of the membraneof the membrane  Sodium gates are shown as closing, open,Sodium gates are shown as closing, open, or closedor closed Propagation of an Action PotentialPropagation of an Action Potential (Time = 0ms)(Time = 0ms)
  29. Propagation of an Action PotentialPropagation of an Action Potential (Time = 0ms)(Time = 0ms) Figure 11.13a
  30.  Ions of the extracellular fluid moveIons of the extracellular fluid move toward the area of greatest negativetoward the area of greatest negative chargecharge  A current is created that depolarizesA current is created that depolarizes the adjacent membrane in a forwardthe adjacent membrane in a forward directiondirection  The impulse propagates away from itsThe impulse propagates away from its point of originpoint of origin Propagation of an ActionPropagation of an Action Potential (Time = 1ms)Potential (Time = 1ms)
  31. Propagation of an ActionPropagation of an Action Potential (Time = 1ms)Potential (Time = 1ms) Figure 11.13b
  32.  The action potential moves away fromThe action potential moves away from the stimulusthe stimulus  Where sodium gates are closing,Where sodium gates are closing, potassium gates are open and create apotassium gates are open and create a current flowcurrent flow Propagation of an ActionPropagation of an Action Potential (Time = 2ms)Potential (Time = 2ms)
  33. Propagation of an Action Potential (TimePropagation of an Action Potential (Time = 2ms)= 2ms) Figure 11.13c
  34.  Threshold – membrane is depolarized by 15 toThreshold – membrane is depolarized by 15 to 20 mV20 mV  Established by the total amount of currentEstablished by the total amount of current flowing through the membraneflowing through the membrane  Weak (subthreshold) stimuli are not relayedWeak (subthreshold) stimuli are not relayed into action potentialsinto action potentials  Strong (threshold) stimuli are relayed intoStrong (threshold) stimuli are relayed into action potentialsaction potentials  All-or-none phenomenon – action potentialsAll-or-none phenomenon – action potentials either happen completely, or not at alleither happen completely, or not at all Threshold and Action PotentialsThreshold and Action Potentials
  35. Absolute Refractory PeriodAbsolute Refractory Period Figure 11.15
  36.  The interval following the absoluteThe interval following the absolute refractory period when:refractory period when:  Sodium gates are closedSodium gates are closed  Potassium gates are openPotassium gates are open  Repolarization is occurringRepolarization is occurring  The threshold level is elevated, allowingThe threshold level is elevated, allowing strong stimuli to increase the frequencystrong stimuli to increase the frequency of action potential eventsof action potential events Relative Refractory PeriodRelative Refractory Period
  37.  Conduction velocities vary widely amongConduction velocities vary widely among neuronsneurons  Rate of impulse propagation isRate of impulse propagation is determined by:determined by:  Axon diameter – the larger the diameter,Axon diameter – the larger the diameter, the faster the impulsethe faster the impulse  Presence of a myelin sheath – myelinationPresence of a myelin sheath – myelination dramatically increases impulse speeddramatically increases impulse speed Conduction Velocities of AxonsConduction Velocities of Axons
  38.  Current passes through a myelinatedCurrent passes through a myelinated axon only at the nodes of Ranvieraxon only at the nodes of Ranvier  Voltage-gated NaVoltage-gated Na++ channels arechannels are concentrated at these nodesconcentrated at these nodes  Action potentials are triggered only atAction potentials are triggered only at the nodes and jump from one node tothe nodes and jump from one node to the nextthe next  Much faster than conduction alongMuch faster than conduction along unmyelinated axonsunmyelinated axons Saltatory ConductionSaltatory Conduction
  39. Saltatory ConductionSaltatory Conduction Figure 11.16

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