Neurons are the basic units of the nervous system. They contain long tubular str

Question

Neurons are the basic units of the nervous system. They contain long tubular structures called axons that propagate electrical signals. An axon contains a solution of positive potassium K+ ions and large negative organic ions. The axon membrane holds the organic ions inside, but the small K+ ions can penetrate the membrane to some degree. This leaves an excess negative charge on the inner surface of the membrane and a positive charge on the outer surface. Measurements show that this potential difference is usually about 70 mV. The thickness of the membrane is 7 nm. We can model it as a sheet with equal and opposite charge densities on opposite sides. (a)Find the electric field inside this membrane, assuming that it is filled with water (K = 80). Which way does it point, into or out of the axon? Which is at higher potential, inner or outer surface of the membrane?

Explanation / Answer

E = V/d = 70e-3/7e-9 = 1 * 10^7 V/m

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