Question

Consider the following for problems 1 through 5:

The concept of electric potential difference plays an important role in the human nervous system. A nervous impulse, for example, is an action potential that results from the temporal rising and lowering of the cell membrane potential, which in turn is caused by the equally temporal influx of sodium (Na+) ions into the cell. The sodium ions enter the cell through Hodgkin-Huxley channels, named after English physiologist/biophysicists Alan Hodgkin and Andrew Huxley. The membrane potential of a resting neuron is known as the resting membrane potential. In problem 1 through 5, consider a neuron whose resting membrane potential is -70 mV.

1. Given that the membrane thickness is 9 x 10^-9m, what is the magnitude of the electric field of the membrane?
   1. 9 x 10⁶V/m
   2. 8 x 10⁶V/m
   3. 7 x 10⁶V/m
   4. 6 x 10⁶V/m
   5. 5 x 10⁶V/m

2. Which of the following about the electric field in the membrane is true?
   1. It is greater near the positive wall and tapers off towards the negative wall.
   2. It is parallel to both the positive and the negative walls.
   3. It points from the outer wall to the inner wall.
   4. It is independent of the amount of charges on either of the walls.
   5. It points radially out from the center of the neuron.

3. When a sodium ion moves from the outer wall to the inner wall, how much work is done by the electric force?
   1. 1 x 10^-20 J
   2. 2 x 10^-20 J
   3. 3 x 10^-20 J
   4. 4 x 10^-20 J
   5. 5 x 10^-20 J

4. Given that the membrane has a surface area of 5 x 10-⁹ m² and assuming that the dielectric constant is 5.0, how much charge resides on the outer wall?
   1. 1 x 10^-12 C
   2. 2 x 10^-12 C
   3. 3 x 10^-12 C
   4. 4 x 10^-12 C

5.Suppose the resistance of a Hodgkin-Huxley channel is 5 x 10⁹ Ω. When a sufficiently strong stimulus is applied to a neuron, the channel becomes open, and sodium ions flood into the cell, creating an action potential. In this situation, on average how many sodium ions would flow in 1 ms?

5. 5 x 10⁴
6. 6 x 10⁴
7. 7 x 10⁴
8. 8 x 10⁴
1. 9 x 10⁴

Answer 1