Bio 224 them 6

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  1. Giant squid Axons
    • •Is very large
    • –up to 1 mm in diameter; typically around 0.5 mm
    • –controls part of the water jet propulsion system;
    • •Is unmyelinated which decreases the conduction velocity potential substantially
  2. Measure of membrane potential
    • -Voltmeter records the voltage difference between the microelectrodes inside and outside the neuron
    • -Measurement made as a function of time
  3. Depolarization
    Decrease in potential. Membrane becomes less negative
  4. Repolarization
    increase in potential. membrane becomes more negative
  5. Hyperpolarization
    increase in potential, membrane more negative
  6. Graded potential
    Change in membrane potential relative to resting potential
  7. charge outside the cell is ___
    charge inside the cell is ___
    • charge outside the cell is positive
    • charge inside the cell is negative
  8. How are membranes depolarized
    A triggering event opens ion channels, usually leading to net Na+ entry that depolarizes the membrane locally
  9. How is depolarization transmitted along a membrane?
    Local current flows between the active and adjacent inactive areas, resulting in  depolarization of the previously inactive areas
  10. What causes decremental spread of graded potential
    • -Leakage of charge-carrying ions (usually potassium) across the plasma membrane
    • -potential dies out altogether within a few millimeters of its site of initiation
  11. ions move through two different types of gated channels
    voltage gated: open and close in response to voltage changes

    ligand gated: open and close in response to ligands or chemicals
  12. 3 Factors Contributing to Resting Potential
    • 1.Na+/K+-ATPase pump
    • 2.Ion channels
    • 3.Negatively charged molecules such as proteins more abundant inside the cell.
  13. Na+/K+-ATPase pump
    transports 3 Na+ out for every 2 K+ moved in
  14. Voltage-gated K+ Channels (leaking channels)
    • –Tend to be open more frequently at the resting membrane potential;
    • –Most neurons have fifty times more potassium channels than sodium channels
    • –Thus at rest the membrane is more permeable to potassium than sodium
    • -activation gate triggered at threshold with delayed opening. (opens 1 msec after Na+)
  15. Voltage gated sodium channel
    -2 features
    • Activation gate
    • deactivation gate
    • both triggered at threshold but deactivation gate takes longer leaving a small window when Na+ can cross membrane
  16. absolute refractory period
    the portion of the membrane that has just undergone an action potential cannot be restimulated
  17. relative refractory periods
    • -the membrane can be restimulated only by a stronger stimulus than is usually necessary
    • -K+ gates not yet closed
    • -lingering inactivation of the voltage-gated Na+ channels.
  18. What does an inward flow of sodium ions cause
    • –A further rise in the membrane potential(more positive)
    • –More channels to open
    • –A greater electric current, and so on
    • -The polarity of the plasma membrane to reverse, and the ion channels then rapidly inactivate
    • -Na+ then actively transported out of the plasma membrane
  19. What prevents "backward" current flow?
    the refractory period
  20. Role of the Nodes of Ranvier
    The only areas of the axon that have enough Na+ channels to elicit an action potential
  21. Saltatory conduction
    action potential seems to “jump” from node to node
  22. graded potentials
    potentials that cause action potentials when they are big enough (or enough coincide) to cross the threshold
  23. Speed of signal transmission is based on:
    • Axon diameter- broadaxons provide less resistance and action potential moves faster-
    • Myelination -myelinated faster then unmyelinated
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Bio 224 them 6
2013-10-07 01:34:28
Bio 224

Bio 224
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