Physiological PsychologyPhysiological Psychology
PSYC-465PSYC-465
11
NeurophysiologyNeurophysiology
Systems and Circuits
What level(s) of analysis?What level(s) of analysis?
Synapses and Neurons
Genes and Molecules
Behavio...
33
Recording the Membrane PotentialRecording the Membrane Potential
Experimental setup to record a neuron’s membrane poten...
44
Resting Membrane PotentialResting Membrane Potential
 Resting potential is -70 mVResting potential is -70 mV
 The ins...
55
Ionic Basis of the Resting PotentialIonic Basis of the Resting Potential
Cl-
Cl-
Cl-
Cl-
Cl-
Cl- Cl-
Cl-
Cl-
Cl-
K+
K+
...
66
Ionic Basis of the Resting PotentialIonic Basis of the Resting Potential
Cl-
Cl-
Cl-
Cl-
Cl-
Cl- Cl-
Cl-
Cl-
Cl-
K+
K+
...
77
Hodgkin & Huxley (1950)Hodgkin & Huxley (1950)
Cl-
Cl-
Cl-
Cl-
Cl-
Cl- Cl-
Cl-
Cl-
Cl-
K+
K+
K+
K+
K+
K+
K+
K+
K+
Na+
N...
88
Hodgkin & Huxley (1950)Hodgkin & Huxley (1950)
 Concluded that there are activeConcluded that there are active
mechani...
99
Sodium-Potassium PumpSodium-Potassium Pump
4)4) Subsequently it wasSubsequently it was
discovered that thediscovered th...
1010
How do neurons talk to each other?How do neurons talk to each other?
 When one neuron fires an action potential,When...
1111
Two Postsynaptic EventsTwo Postsynaptic Events
 DepolarizationDepolarization – decreases the resting– decreases the ...
1212
Postsynaptic Potentials (PSPs)Postsynaptic Potentials (PSPs)
 Depolarizations are calledDepolarizations are called E...
1313
Postsynaptic Potentials (PSPs)Postsynaptic Potentials (PSPs)
 Both EPSPs and IPSPs areBoth EPSPs and IPSPs are grade...
1414
Postsynaptic Potentials (PSPs)Postsynaptic Potentials (PSPs)
 PSPs travel passively from the site ofPSPs travel pass...
1515
Integration of PSPs and GenerationIntegration of PSPs and Generation
of Action Potentials (APs)of Action Potentials (...
1616
IntegrationIntegration
 Adding or combining a number ofAdding or combining a number of
individual signals into one o...
1717
SpatialSpatial
SummationSummation
Local PSPsLocal PSPs
producedproduced
simultaneouslysimultaneously
on different par...
1818
TemporalTemporal
SummationSummation
PSPs produced inPSPs produced in
rapid successionrapid succession
at the sameat t...
1919
Comparison ofComparison of
PSPs and APsPSPs and APs
In contrast to PSPs, theIn contrast to PSPs, the
AP is a massiveA...
2020
Comparison of PSPs and APsComparison of PSPs and APs
EPSPs/IPSPsEPSPs/IPSPs APsAPs
Graded events – theyGraded events ...
2121
Sodium
channel
Na+
K+
A--
Na+Na+
Na+
Na+
Na+
Na+
A--
A--
A--
A--
K+
K+
K+
K+
Cl-
Cl-
Cl-
Cl-
Cl-
+
-
+
-
+
-
Potassiu...
2222
Ionic Basis of the APIonic Basis of the AP
2323
Refractory PeriodsRefractory Periods
 Absolute refractoryAbsolute refractory – a brief– a brief
period (1-2 ms) afte...
2424
Refractory PeriodsRefractory Periods
Refractory periods areRefractory periods are
responsible for tworesponsible for ...
2525
Saltatory ConductionSaltatory Conduction
Transmission of APs in myelinatedTransmission of APs in myelinated
axons –ax...
2626
How fast are APs?How fast are APs?
Conduction speed depends on:Conduction speed depends on:
1.1. Diameter of axon (fa...
2727
Conduction in Myelinated AxonsConduction in Myelinated Axons
 Passive movement of AP within myelinatedPassive moveme...
2828
The Changing View of Dendritic FunctionThe Changing View of Dendritic Function
Three recently discovered characterist...
2929
Overview of Neural signalsOverview of Neural signals
1)1) EPSPs and IPSPs (PSPs) are graded eventsEPSPs and IPSPs (PS...
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PSYC465 - neurophysiology.ppt

  1. 1. Physiological PsychologyPhysiological Psychology PSYC-465PSYC-465 11 NeurophysiologyNeurophysiology
  2. 2. Systems and Circuits What level(s) of analysis?What level(s) of analysis? Synapses and Neurons Genes and Molecules Behavior and Cognition
  3. 3. 33 Recording the Membrane PotentialRecording the Membrane Potential Experimental setup to record a neuron’s membrane potentialExperimental setup to record a neuron’s membrane potential Membrane potential – theMembrane potential – the difference in electricaldifference in electrical charge between thecharge between the inside and outside of ainside and outside of a cell.cell. 1)1) The tip of one electrodeThe tip of one electrode is positioned outside theis positioned outside the neuron.neuron. 2)2) The tip of a fineThe tip of a fine microelectrode (1/1,000microelectrode (1/1,000 mm) is advanced until itmm) is advanced until it pierces the membranepierces the membrane and is positioned insideand is positioned inside the neuron.the neuron.
  4. 4. 44 Resting Membrane PotentialResting Membrane Potential  Resting potential is -70 mVResting potential is -70 mV  The inside of the neuron is 70 mVThe inside of the neuron is 70 mV less than the outsideless than the outside (extracellular fluid).(extracellular fluid).  The neuron is said to beThe neuron is said to be polarizedpolarized – a -70 mV charge is built up– a -70 mV charge is built up across the membrane.across the membrane.
  5. 5. 55 Ionic Basis of the Resting PotentialIonic Basis of the Resting Potential Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- K+ K+ K+ K+ K+ K+ K+ K+ K+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Ions are charged particles. There areIons are charged particles. There are more negative ions relative to positivemore negative ions relative to positive ones inside the neuron. This is due toones inside the neuron. This is due to the interaction of 4 factors (2 act tothe interaction of 4 factors (2 act to distribute ions evenly and 2 aredistribute ions evenly and 2 are features of the cell membrane):features of the cell membrane): 1)1) Random motionRandom motion - particles in- particles in constant motion move down theirconstant motion move down their concentration gradientsconcentration gradients .. 2)2) Electrostatic pressureElectrostatic pressure – like– like charges repel, opposites attract.charges repel, opposites attract. • No single class of ions is distributedNo single class of ions is distributed evenly across both sides of the cellevenly across both sides of the cell membrane.membrane. • Sodium (NaSodium (Na++ ) and chloride (Cl) and chloride (Cl-- ) are) are greater outside.greater outside. • Potassium (KPotassium (K++ )) and large protien ions (Anions; A-- ) are greater inside. A-- A-- A-- A-- A-- A-- A--
  6. 6. 66 Ionic Basis of the Resting PotentialIonic Basis of the Resting Potential Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- K+ K+ K+ K+ K+ K+ K+ K+ K+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ 3)3) Differential permeabilityDifferential permeability – The– The membrane has specialized poresmembrane has specialized pores called ion channels for each kind ofcalled ion channels for each kind of ion.ion. • Potassium (K+) and chloride (ClPotassium (K+) and chloride (Cl-- ) ions) ions pass readily through their channels.pass readily through their channels. • Sodium (NaSodium (Na++ )) ions pass through with difficulty. • Large protien ions (A-- ) are trapped inside. IF some ions can pass through the membrane then what prevents them from flowing down their concentration gradients? IS it electrostatic pressure? A-- A-- A-- A-- A-- A-- A--
  7. 7. 77 Hodgkin & Huxley (1950)Hodgkin & Huxley (1950) Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- K+ K+ K+ K+ K+ K+ K+ K+ K+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ To answer the questionTo answer the question Hodgkin & HuxleyHodgkin & Huxley calculated the amountcalculated the amount of electrostatic chargeof electrostatic charge that would be requiredthat would be required for each ion that canfor each ion that can pass through thepass through the membrane (Cl-, K+membrane (Cl-, K+ and Na+) to moveand Na+) to move down theirdown their concentrationconcentration gradients.gradients. A-- A-- A-- A-- A-- A-- A-- 70 mV from CG 70 mV from ES 90 mV from CG 70 mV from ES 50 mV from CG 70 mV from ES
  8. 8. 88 Hodgkin & Huxley (1950)Hodgkin & Huxley (1950)  Concluded that there are activeConcluded that there are active mechanisms in the cell membranemechanisms in the cell membrane to counteract the passive influxto counteract the passive influx (inflow) of Na+ ions and the(inflow) of Na+ ions and the passive efflux (outflow) of K+passive efflux (outflow) of K+ ions.ions.
  9. 9. 99 Sodium-Potassium PumpSodium-Potassium Pump 4)4) Subsequently it wasSubsequently it was discovered that thediscovered that the sodium-potassiumsodium-potassium pumppump exchanges 3exchanges 3 sodium ions out of thesodium ions out of the neuron for every 2neuron for every 2 potassium ions broughtpotassium ions brought into the neuron. This isinto the neuron. This is an active mechanism thatan active mechanism that requires energy (ATP) torequires energy (ATP) to maintain the restingmaintain the resting membrane potential.membrane potential. NaNa++ NaNa++ NaNa++ KK++ KK++
  10. 10. 1010 How do neurons talk to each other?How do neurons talk to each other?  When one neuron fires an action potential,When one neuron fires an action potential, it causes the release of neurotransmitterit causes the release of neurotransmitter molecules into the small space thatmolecules into the small space that separates the terminal bouton from theseparates the terminal bouton from the receptive portion of the neuron (e.g., areceptive portion of the neuron (e.g., a dendritic spine). The space is called thedendritic spine). The space is called the synapsesynapse..  Neurotransmitter molecules bind toNeurotransmitter molecules bind to receptors on the next neuron, causing onereceptors on the next neuron, causing one of two events.of two events.
  11. 11. 1111 Two Postsynaptic EventsTwo Postsynaptic Events  DepolarizationDepolarization – decreases the resting– decreases the resting membrane potential (e.g., from -70 to -67membrane potential (e.g., from -70 to -67 mV).mV).  HyperpolarizationHyperpolarization – increases the– increases the resting membrane potential (e.g., from -70resting membrane potential (e.g., from -70 to -72 mV).to -72 mV).
  12. 12. 1212 Postsynaptic Potentials (PSPs)Postsynaptic Potentials (PSPs)  Depolarizations are calledDepolarizations are called ExcitatoryExcitatory postsynaptic potentials (EPSPs)postsynaptic potentials (EPSPs) –– they increase the likelihood that thethey increase the likelihood that the postsynaptic (receiving) neuron will itselfpostsynaptic (receiving) neuron will itself generate an action potential.generate an action potential.  Hyperpolarizations are calledHyperpolarizations are called InhibitoryInhibitory postsynaptic potentials (IPSPs)postsynaptic potentials (IPSPs) –– they decreases the likelihood that thethey decreases the likelihood that the postsynaptic neuron will generate anpostsynaptic neuron will generate an action potential.action potential.
  13. 13. 1313 Postsynaptic Potentials (PSPs)Postsynaptic Potentials (PSPs)  Both EPSPs and IPSPs areBoth EPSPs and IPSPs are gradedgraded eventsevents – i.e., the amplitudes of both– i.e., the amplitudes of both PSPs are proportional to the intensityPSPs are proportional to the intensity of the signal (they come in differentof the signal (they come in different sizes).sizes).  Weak signals generate small PSPsWeak signals generate small PSPs and strong signals elicit large PSPs.and strong signals elicit large PSPs.
  14. 14. 1414 Postsynaptic Potentials (PSPs)Postsynaptic Potentials (PSPs)  PSPs travel passively from the site ofPSPs travel passively from the site of origin, similar to the way an electricalorigin, similar to the way an electrical signal travels through a cable.signal travels through a cable.  Accordingly, PSPs travel fast but areAccordingly, PSPs travel fast but are decrementaldecremental (i.e., they decrease in(i.e., they decrease in amplitude the further they travel).amplitude the further they travel).
  15. 15. 1515 Integration of PSPs and GenerationIntegration of PSPs and Generation of Action Potentials (APs)of Action Potentials (APs)  In order to generate an AP (making aIn order to generate an AP (making a neuron “fire”) theneuron “fire”) the threshold ofthreshold of excitationexcitation must be reached at themust be reached at the beginning section of the axon, near thebeginning section of the axon, near the axon hillock.axon hillock.  Integration of IPSPs and EPSPs mustIntegration of IPSPs and EPSPs must result in a potential of about -65mV inresult in a potential of about -65mV in order to generate an APorder to generate an AP
  16. 16. 1616 IntegrationIntegration  Adding or combining a number ofAdding or combining a number of individual signals into one overallindividual signals into one overall signal.signal.  Temporal summationTemporal summation – integration– integration of events happening at differentof events happening at different times.times.  Spatial summationSpatial summation - integration of- integration of events happening at different places.events happening at different places.
  17. 17. 1717 SpatialSpatial SummationSummation Local PSPsLocal PSPs producedproduced simultaneouslysimultaneously on different partson different parts of the neuronof the neuron sum to producesum to produce greater PSPs orgreater PSPs or cancel eachcancel each other out.other out.
  18. 18. 1818 TemporalTemporal SummationSummation PSPs produced inPSPs produced in rapid successionrapid succession at the sameat the same synapse sum tosynapse sum to form a greaterform a greater signal.signal.
  19. 19. 1919 Comparison ofComparison of PSPs and APsPSPs and APs In contrast to PSPs, theIn contrast to PSPs, the AP is a massiveAP is a massive mommentary reversalmommentary reversal of the membraneof the membrane potential from -70 mVpotential from -70 mV to +50 mV.to +50 mV.
  20. 20. 2020 Comparison of PSPs and APsComparison of PSPs and APs EPSPs/IPSPsEPSPs/IPSPs APsAPs Graded events – theyGraded events – they come in different sizescome in different sizes All-or-none – like firing aAll-or-none – like firing a gungun Not propagated – theyNot propagated – they travel by passive cabletravel by passive cable propertiesproperties Propagated – once theyPropagated – once they begin they travel all thebegin they travel all the way down the axonway down the axon Decremental – theDecremental – the farther they go thefarther they go the weaker the getweaker the get Nondecremental – theNondecremental – the height is the same fromheight is the same from beginning to endbeginning to end
  21. 21. 2121 Sodium channel Na+ K+ A-- Na+Na+ Na+ Na+ Na+ Na+ A-- A-- A-- A-- K+ K+ K+ K+ Cl- Cl- Cl- Cl- Cl- + - + - + - Potassium channel K+ K+ Sodium channelK+ + - + - + - Na+ Na+ Sodium channel Na+ Ionic Basis of the APIonic Basis of the AP
  22. 22. 2222 Ionic Basis of the APIonic Basis of the AP
  23. 23. 2323 Refractory PeriodsRefractory Periods  Absolute refractoryAbsolute refractory – a brief– a brief period (1-2 ms) after the initiation ofperiod (1-2 ms) after the initiation of an AP during which it is not possiblean AP during which it is not possible to elicit another AP.to elicit another AP.  Relative refractoryRelative refractory – the period in– the period in which it is possible to fire an AP, butwhich it is possible to fire an AP, but only if higher-than-normal levels ofonly if higher-than-normal levels of stimulation are applied.stimulation are applied.
  24. 24. 2424 Refractory PeriodsRefractory Periods Refractory periods areRefractory periods are responsible for tworesponsible for two characteristics of neuralcharacteristics of neural conduction:conduction: 1.1. APs normally travel in oneAPs normally travel in one direction.direction. 2.2. Rate of neural firing is relatedRate of neural firing is related to the intensity of theto the intensity of the stimulation.stimulation.
  25. 25. 2525 Saltatory ConductionSaltatory Conduction Transmission of APs in myelinatedTransmission of APs in myelinated axons –axons – saltaresaltare (to “skip” or “jump”).(to “skip” or “jump”).  AP conduction along myelinatedAP conduction along myelinated segments of an axon is passive.segments of an axon is passive.  i.e., it travels fast but gets weakeri.e., it travels fast but gets weaker the farther it goes.the farther it goes.  The signal is still strong enough toThe signal is still strong enough to generate a full AP at the next node.generate a full AP at the next node.
  26. 26. 2626 How fast are APs?How fast are APs? Conduction speed depends on:Conduction speed depends on: 1.1. Diameter of axon (faster in largeDiameter of axon (faster in large axons).axons). 2.2. Myelination (faster in myelinatedMyelination (faster in myelinated axons).axons).
  27. 27. 2727 Conduction in Myelinated AxonsConduction in Myelinated Axons  Passive movement of AP within myelinatedPassive movement of AP within myelinated portions occurs instantlyportions occurs instantly  Nodes of Ranvier (unmyelinated)Nodes of Ranvier (unmyelinated) – Where ion channels are foundWhere ion channels are found – Where full AP is seenWhere full AP is seen – AP appears to jump from node to nodeAP appears to jump from node to node  Saltatory conductionSaltatory conduction  http://www.brainviews.com/abFiles/AniSalt.htmhttp://www.brainviews.com/abFiles/AniSalt.htm
  28. 28. 2828 The Changing View of Dendritic FunctionThe Changing View of Dendritic Function Three recently discovered characteristics ofThree recently discovered characteristics of dendrites:dendrites: 1.1. Some can generate APs that travel inSome can generate APs that travel in either direction.either direction. 2.2. Dendritic spines restrict chemicalDendritic spines restrict chemical changes to the immediate area of thechanges to the immediate area of the synapse (they compartmentalize thesynapse (they compartmentalize the dendrite).dendrite). 3.3. Spines change rapidly (within minutes toSpines change rapidly (within minutes to hours) in shape and number in responsehours) in shape and number in response to neural stimulation.to neural stimulation.
  29. 29. 2929 Overview of Neural signalsOverview of Neural signals 1)1) EPSPs and IPSPs (PSPs) are graded eventsEPSPs and IPSPs (PSPs) are graded events initiated by the action of neurotransmittersinitiated by the action of neurotransmitters binding to receptors on the postsynapticbinding to receptors on the postsynaptic membrane.membrane. 2)2) PSPs summate spatially and temporallyPSPs summate spatially and temporally 3)3) If EPSP signals are greater, causing a changeIf EPSP signals are greater, causing a change in membrane potential (depolarization) to -64in membrane potential (depolarization) to -64 mV (threshold of exitation) at the beginningmV (threshold of exitation) at the beginning segment of the axon, then the postsynapticsegment of the axon, then the postsynaptic neuron will fire an APneuron will fire an AP 4)4) Once initiatiated the AP travels the full lengthOnce initiatiated the AP travels the full length of the axon to the terminal buttons.of the axon to the terminal buttons.
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