The potential difference and the direction of the electric field across the memb

Question

The potential difference and the direction of the electric field across the membrane of an axon in its rest state would be:
A. Positive on the exterior of the cell with lines of force running from the outside to the inside B. Positive on the exterior of the cell with lines of force running from the inside to the outside C. Negative on the exterior of the cell with lines of force running from the outside to the inside D. Negative on the exterior of the cell with lines of force running from the inside to the outside
Ion flow in neurons can be characterized as an electrical circuit for both the resting neuron (Fig. 1) and the active neuron (Fig. 2). In Figure 1, the axon membrane can be treated as a capacitor, slow leakage channels as a 2.5 x 107 resister, and the Na+K' pump as a voltage generator. The voltage across the membrane is -70 mV from the exterior to the interior of the cell. Figure 2 includes the additional Na+ influx (a 4.0 x 103 resistor) of an action potential (AP). Other ion fluxes are ignored.

Explanation / Answer

Given that the potential across the membrane is -70 mV in the rest state from the exterior to the interior. Therefore the potential is negative on the exterior of the cell and field lines of force run from positive to negative. So the field lines run from interior of the cell to exterior.

Option D is correct.

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