How many K* ions are on the outside of the axon assuming an initial potential difference of 7.0 x 10-2 v? 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 (Å2). An atom has a cross section of about 1 Å? (1 Å = 10-10 m). (Compare to normal atomic spacing of one atom every few Å.) Yes O No (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? How many sodium ions (Na*) is this? Nat ions (c) If it takes 2.0 ms for the Na* ions to enter the axon, what is the average current in the axon wall in this process? (d) How much energy does it take to raise the potential of the inner axon wall to +3.0 × 10¬2 v, starting from the resting potential of –7.0 × 10¬2 v? (Assume that no energy is required to first raise the potential to 0 V from the resting potential of -7.0 × 10¬2 v.)

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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
%D
resting state, the outer surface of the axon wall is charged positively with Kt ions and the inner wall has an 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 = KƐ A/d and Q = CAV to investigate the charge as follows. Use typical values for a cylindrical axon of cell
-8
wall thickness d = 1.5 x 10 m, axon radius r =
2.0 x 10- um, and cell-wall dielectric constant K =
2.9.
External fluid
+
Positive
charge
layer
Axon wall membrane
d
Negative
charge
layer
Internal fluid
Axon radius = r
(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.)
1.035E-9
Your response differs from the correct answer by more than 10%. Double check your calculations. C
Transcribed Image Text: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 %D resting state, the outer surface of the axon wall is charged positively with Kt ions and the inner wall has an 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 = KƐ A/d and Q = CAV to investigate the charge as follows. Use typical values for a cylindrical axon of cell -8 wall thickness d = 1.5 x 10 m, axon radius r = 2.0 x 10- um, and cell-wall dielectric constant K = 2.9. External fluid + Positive charge layer Axon wall membrane d Negative charge layer Internal fluid Axon radius = r (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.) 1.035E-9 Your response differs from the correct answer by more than 10%. Double check your calculations. C
How many K* ions are on the outside of the axon assuming an initial potential difference of 7.0 x 10-2 v?
Kt 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 (Å2). An atom has a cross section of
about 1 Å2 (1 Å = 10¬10 m). (Compare to normal atomic spacing of one atom every few Å.)
%3D
Yes
No
(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?
How many sodium ions (Na*) is this?
Nat ions
+
(c) If it takes 2.0 ms for the Nat ions to enter the axon, what is the average current in the axon wall in this process?
µA
-2
(d) How much energy does it take to raise the potential of the inner axon wall to +3.0 x 10 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
Transcribed Image Text:How many K* ions are on the outside of the axon assuming an initial potential difference of 7.0 x 10-2 v? Kt 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 (Å2). An atom has a cross section of about 1 Å2 (1 Å = 10¬10 m). (Compare to normal atomic spacing of one atom every few Å.) %3D Yes No (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? How many sodium ions (Na*) is this? Nat ions + (c) If it takes 2.0 ms for the Nat ions to enter the axon, what is the average current in the axon wall in this process? µA -2 (d) How much energy does it take to raise the potential of the inner axon wall to +3.0 x 10 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
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