PSY 241 Lecture 3

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PSY 241 Lecture 3
2013-02-14 18:19:44
PSY 241 Psychobiology Arturo Zavala

PSY 241 Psychobiology Arturo Zavala
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  1. Depolarization
    • Decrease in membrane potential
    • Interior of cell becomes less negatively and closer to zero

    • Accomplished in 2 ways:
    • Negative ions leave cell
    • Positive ions come into cell
  2. Hyperpolarization
    • Increase in membrane potential
    • Interior of membrane becomes more negative and farther from zero

    • Accomplished in 2 ways:
    • Negative ions come into the cell
    • Positive ions leave the cell
  3. Graded potential (response)
    • Change in potential
    • The greater the stimulus, the greater the response
  4. As the potential spreads across the membrane, it
    diminishes (weakens) as it moves away from the point of stimulation
  5. Action potentials
    • Quick large electrical pulses in the membrane of the axon
    • not the dendrites or cell body
    • Triggered by positive current applied to the axon hillock
    • Voltage-dependent
    • Rapid reversal of membrane potential from -40MV to +40mV
  6. Five Phases of Action Potential
    • Depolarization phase
    • Threshold phase
    • Rising phase
    • Falling phase
    • Hyperpolarized (Undershoot)
  7. Depolarization Phase
    • -60 to -40 mV
    • Inside of cell becomes more positive as a result of an excitatory stimulus
    • graded potentials or positive current injected via a microelectrode
  8. Threshold Phase
    • -40 mV
    • Level of stimulation required for neuron to produce action potential
    • Represents opening of voltage-gated ion channels (ion channel sensitive to changes in cell membrane potential)
    • Voltage-gated sodium channels present at axon hillock
  9. Voltage-Gated Sodium Channels
    • Closed at RMP, -60 mV
    • Open when membrane is depolarized (-40 mV - Threshold)
    • Only allow Sodium to pass through
    • Time-dependent (only open for one millisecond) and close by inactivation gate
  10. Rising Phase
    • -40 mV to +40 mV
    • Sodium rushes into cell via voltage-gated sodium channels causing membrane to be more positive

    • At end of phase, Voltage-gated potassium channels being to open:
    • less sensitive to changes in membrane potential
    • only allow passage of K+
    • once open, they do no close until neuron reach RMP (Closing is slow)
    • Voltage-gated sodium channels close at peak (+40 mV)
  11. Falling Phase
    • +40 mV to -60 mV
    • Potassium rushes out of cell via voltage-gated potassium channels causing membrane potential to become more negative
  12. Hyperpolarized (Undershoot) Phase
    • -60 mV to -70 mV
    • Voltage-gated potassium channels close slowly, potassium continues to leave the cell, thereby creating a membrane potential that is more negative than normal (-70 mV)
    • *Equilibrium potential for K+ is -90 mV
  13. Recovery of resting membrane potential
    • -70 mV
    • Sodium/Potassium Pump restores membrane potential to RMP
    • Passive Chloride ions are also open
  14. Absolute Refractory Period
    • Time neuron is insensitive to further stimulation
    • Starts at peak of action potential and continues though falling phase
    • Result of function of voltage-gated sodium channels
    • Inactivation gate blocks channel and does not reset until membrane has reached RMP
  15. Relative Refractory Period
    • Time following the absolute refractory period during which a neuron can generate another action potential but only by a stronger than normal stimulus
    • Occurs during the hyperpolarized phase (-60 mV to -70 mV)
  16. Intensity of Stimuli encoded by:
    • Firing rate of a neuron (Rate Law):
    • The more intense the stimulus, the faster the rate of action potentials

    • Number of neurons firing action potential:
    • The more intense stimuli can cause more neurons to fire an action potential
  17. Unmyelinated Axons
    • Sodium rushing in via voltage-gated sodium channels and depolarizes the membrane, which triggers the opening of adjacent voltage-gated sodium channels
    • Continues until action potential reaches terminal button
    • Activated voltage-gated ion channels will enter into absolute refractory period, so action potential cannot be initiated again and signal does not travel back
  18. Multiple Sclerosis
    • 200 Americans, mostly women, are diagnosed
    • neurological disease
    • autoimmune disease damages myelin sheat around axons

    • Symptoms:
    • Tingling sensation and/or numbness: toes or fingers
    • Seeing double, blurry vision
    • Abnormal fatigue