lecture 4-voltage clamp-2-1

lecture 4-voltage clamp-2-1 - Todays Lecture ) Review...

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1 Today’s Lecture 1) Review voltage gated channels and how they generate action potentials. 2) Voltage Clamping and how those channels were first discovered
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2 Electrical pulse (Action Potential) starts here Release of neurotransmitter + + + + Neurotransmitter binds to receptor and opens an ion channel. Positive current is injected into neuron carried by Na+ + -
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3 In thinking about action potentials, keep your eye on the ball ! The whole idea of the action potential is to transmit information: 1) Over long distances 2) With high fidelity, so that the same action potential that appears near the cell body, appears at the terminal a short time later. 3) Rapidly
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4 ------------ -------------- ---------------- ------------- +++ ++++ ++++ ++ +++ ++++ ++++ ++ +++++++++ +++++ ++ Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + -70 mV +50 mV Membrane potential The sequence of events leading to an AP is set in motion when a portion of the inside of the cell is depolarized + + + + + + + + +
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5 Problem: The cell has to get rid of the excess positive charges brought in by Na+ so that the membrane can repolarize (inside of cell becomes negative). When the cell repolarizes, the negative charges on the inside of the cell reset the activation and inactivation gates and thereby allow another action potential to be generated. ------- ------- +++++ ++++++ Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + +50 mV inside positive
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6 _ _ + + K + K K + K + K + Voltage Gated Na+ Channel Voltage Gated K+ Channel Solution : The axon has another type of voltage gated channel, also opened by positive charges, but this channel is permeable only to K+. The K+ channel only has an activation gate that opens somewhat more slowly than the activation gates of the Na channel. So after the Na channels are open, the K+ channel opens and allows positive charge to leave the cell, but the positive charges leaving the cell are carried by K+! Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + K + K + K + _ _ _ _ _ _ _ _ _ _ _ _ _ _ + + + + + + + + + + + + + + + -75 mV
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7 Due to the loss of positive charges from the inside of the cell, the inside now approaches the K+ equilibrium potential of -75 mV, and thus becomes very negative. The negative charges then cause the gates to reset. K + K + Na + K K + Voltage Gated Na+ Channel Voltage Gated K+ Channel Na + Na + Na + Na + Na + Na + K + Na + Na + Na + K + K + K + _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ + + + + + + + + + + + + + + + -75 mV
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8 K + K + K + K + K + Na + Na + Na + Na + Na + Na + Na + Na + Na + K + K + K + _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ + + + + + + + + + + + + + + + -70 mV Channels are closed at Rest
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9 K + K + K + Na + Na + Na + Na + Na + Na + Na + K + K + K + -75 mV _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ + + + + + + + + + + + + + + + + + + + + + + + + Here is the entire sequence- First the membrane slightly depolarizes (inside becomes slightly more positive ). This causes Na activation gate to open and a moment later the Na inactivation gate to close. Na + Na + Na + + K + K + _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ + + + + + + + + + + + + + + + + + + + + + + + + Next, the K+ activation gate opens and repolarizes the cell Finally, the negative charges on the inside of the cell causes the gates in the Na and K channels to reset. The cell is now back to its resting potential -70 mV K +
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10
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11 + + + Why doesn’t this action potential back propagate?
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This note was uploaded on 10/25/2010 for the course BIO 365R taught by Professor Draper during the Spring '08 term at University of Texas at Austin.

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lecture 4-voltage clamp-2-1 - Todays Lecture ) Review...

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