CN2011 Problem Set # 1

# CN2011 Problem Set # 1 - Problem set 1 2011 Problem 1 Axon...

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Problem set 1 2011 page 1 Problem 1 Axon ion movements The squid axon has a specific membrane capacitance of 10 -6 Farads/cm 2 . The membrane potential is -65 mV at rest and +45 mV at the peak of the action potential. When the membrane potential changes, the charge on the membrane capacitance changes. A. 1. How many Na + ions must enter the axon per square centimeter of axon membrane to change the charge from the resting potential to the peak action potential? 2. How many K + ions must leave to return the potential to rest? B. 1. For an axon which is 400 μm in diameter, what is the surface area of a 1 cm length of axon? 2. How many Na + ions must enter the axon per centimeter of axon length to change the charge from the resting potential to the peak action potential? 3. How many K + ions must leave to return the potential to rest? C. 1. For an axon which is 350 μm in diameter, what is the volume of a 1 cm length of axon? 2. The intracellular ion concentrations for the squid axon are [Na + ] = 55 mM and [K + ] = 410 mM. What changes in the internal ion concentrations for Na + and K + occur during an action potential if the only ion movement is to charge and discharge the membrane capacitance? D. 1. If we inhibited the Na/K ATPase with ouabain, how many action potentials could the axon carry before the internal [Na + ] doubled? E. Actual measurements from isotope fluxes per impulse in squid axon give the following values: net influx of Na + = 3.6x10 -12 moles of Na + per cm 2 of axon membrane per impulse net efflux of K + = 4.0x10 -12 moles of K + per cm 2 of axon membrane per impulse 1. Why are these values larger than the net flux values you calculated from the amount of charge required to charge and discharge the capacitance? 2. With these actual flux measurements, how many impulses could the axon carry for question 1D? F. Say that we now examine a small unmyelinated axon in a mammal, with diameter 1 μm. The intracellular ion concentrations are [Na + ] = 25 mM and [K + ] = 110 mM. 1. With the same value for surface capacitance and resting and peak action potential voltage, how

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CN2011 Problem Set # 1 - Problem set 1 2011 Problem 1 Axon...

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