Assume a length of axon membrane of about 0.10 m is excited by an action potential (length excited nerve speed x pulse duration 50.0 m/s x 0.0020 s= 0.10 m). In the resting state, the outer surface of the axon wall is charged positively with K* ions and the inner wall h equal and opposite charge of negative organic ions, as shown in the figure below. Model the axon as a parallel-plate capacitor and take C = x A/d and Q = CAV to investigate the charge as follows. Use typical values for a cylindrical axon of cell wall thickness d = 2.0 x 10-8 m, radius r= 1.6 x 10¹ μm, and cell-wall dielectric constant x = 2.9. Positive charge layer Negative { charge layer External fluid + + - Axon wall membrane Internal fluid No Axon radius r + d (a) Calculate the positive charge on the outside of a 0.10-m piece of axon when it is not conducting an electric pulse. (Assume an initial potential difference of 7.0 x 10-² V.) 9.03E-10 How many K* ions are on the outside of the axon assuming an initial potential difference of 7.0 x 10-² V? 5.639E9 K+ ions Is this a large charge per unit area? Hint: Calculate the charge per unit area in terms of electronic charge e per angstrom squared (A2). An atom has a cross section of about 1 A² (1 A = 10-10 m). (Compare to normal atomic spacing of one atom every few Å.) O Yes (b) How much positive charge must flow through the cell membrane to reach the excited state of +3.0 x 10-2 V from the resting state of -7.0 x 10-2 V? x Your response differs significantly from the correct answer. Rework your solution from the beginning and check each step carefully. C How many sodium ions (Na+) is this? x Your response differs significantly from the correct answer. Rework your solution from the beginning and check each step carefully. Na+ ions (c) If it takes 2.0 ms for the Nations to enter the axon, what is the average current in the axon wall in this process? x Your response differs from the correct answer by more than 10%. Double check your calculations. A (d) How much energy does it take to raise the potential of the inner axon wall to +3.0 x 10-2 V, starting from the resting potential of -7.0 x 10-2 v? (Assume that no energy is required to first raise the potential to 0 V from the resting potential of -7.0 x 10-² V.) J