lecture_10_26

# lecture_10_26 - Rule: When a (receptor) channel opens Vm...

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-75 mv -67 mv +20 mv -60 mv E F E Cl RMP E R = 57.5 log p Fl [F - ] in + p Cl [Cl - ] in p Fl [F - ] out + p Cl [Cl - ] out Rule: When a (receptor) channel opens V m will go towards, but not beyond, E R of the channel. Exception: if the I-V curve is not a straight line (like the Mg block in discussion section) this rule will not always apply [ ] Rule: the reversal potential must fall between the equilibrium potentials of all ions to which the receptor/channel is permeable The reversal potential for a receptor/channel can be calculated using the GHK equation Corollary rule: when a channel closes V m will go away from E R of the receptor IV.F. What about when a (receptor) channel is permeable to more than one ion type? IV.F.1 You can use the GHK to calculate ER if you know permeabilities and concentrations IV.F.2 Two rules that apply for the equilibrium potentials also apply to reversal potentials

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time Postsynaptic voltage Presynaptic stimulus time -65 -60 -40 Could a receptor with the following post-synaptic potential be permeable to both sodium and potassium but not Cl - ? Yes, If the receptor were permeable to both K + and Na + , the reversal potential would be between -83 and +40 mV. Therefore either a depolarizing or hyperpolarizing psp from E m could result depending on the receptor’s relative permeabilities to Na + and K + . Therefore the observed depolarization to between -60 and -65 mV CANNOT be used to rule out that the receptor is permeable to both K + and NA + , but not to Cl - IV.F.3 We simplified things before; there are a lot more possibilities for inductive reasoning
This overview covers the first 1/3 of the class Overview of a neural circuit: Duckman steps on pebble When Duckman steps on the pebble, this opens ion channels in specialized nerve cells called somatosensory receptors at the bottom of his foot. The channels are located in a part of these specialized nerve cells called free-nerve-endings. When these channels open, the voltage of a somatosensory receptor cell near the channels increases.

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## This note was uploaded on 11/22/2009 for the course NPB 100 taught by Professor Chapman during the Fall '08 term at UC Davis.

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lecture_10_26 - Rule: When a (receptor) channel opens Vm...

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