Nerve cell membrane, capacitance

The nerve cell membrane, which is about 5 nm thick, consists primarily of lipids and proteins. When at rest it is permeable basically to potassium ions (although its resistance in this state is rather high, ca. 10 fl cm ), and therefore the electric potential difference between the inner and outer solutions (this difference is called the membrane potential or simply the potential) is negative at rest and amounts to a few tens of mV (about -60 mV on the giant axon). The membrane capacitance is of the order of 1 /iF/cm. Thus a neuron membrane is already polarized when at rest. If some external action shifts the potential from its value at rest to more negative values (its absolute value increasing), the resultant situation is usually called hyperpolarization. Potential shift in the positive direction is called depolarization. If the potential reverses its sign and becomes positive the term is overshoot. ... 

EXAMPLE 21.3 The capacitance of a nerve cell membrane. Assume that a nerve cell is a long cylinder enclosed by a thin planar bilayer membrane of lipids (see Figure 21.7). You can treat the lipid bilayer as a parallel plate capacitor. Lipid bilayers have oil-like interiors, for which we will assume D = 2, and thickness approximately d 20 A. Equation (21.13) gives the capacitance per unit area as... 

Biological membranes are capacitors. Let s calculate the capacitance of the membrane of a nerve cell. 

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