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Lecture 4

Lecture 4 on Neurons

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University of Toronto Scarborough
Biological Sciences

BIOB30Fall2011 Chapter 8 Neurons Cellular and Network PropertiesLecture 4 Overviewat RMP 70mV there is a high K IC and Na ECat RMP the inside of the cell is negatively charged compared to the outside of the cell depolarization less negative than 55mV causes the opening of voltage gated K and Na channelsNa moves into the cell and K moves out of the cellNa influx causes depolarizationexcitation of the membrane more positive membrane potentialK eflux causes repolarizationhyperpolarization of the membrane more negative potential so the cell becomes less excitablegraded potentials GPs are generated in the cell body by opening and closing the voltage gated Na and K channelsthe size of GPs is directly proportional to the size of the stimulus causing itif GPs caused membrane depolarization is less negative than 55mV at the trigger zone an action potential is generatedaction potentials are generated at the trigger zone by opening and closing of voltage gated Na and K channelsaction potentials are always about the same size 100mVLocation of the Voltage Gated Sodium and Potassium Channelsin the NeuronNa and K channels are located in dendrites and the cell bodyhigh concentration of Na channels found in the trigger zone and between the myelin sheaths in the nodes of RanvierNo Na channels are located where the myelin sheath are on the axonthe same type of ion channels cause graded potentials and action potentialsNa and K channelsNa Entry Creates a Positive Feedback Loopthe depolarization caused by the opening of the Na channels causes more voltage gated Na channels and K channels to open this is referred to as positive feedbackaction potentials are caused by the opening of many Na channels the positive feedback loop generated by Na allows conduction of the action potential down
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