Mathematical Models
The term driving force is related to equilibrium potential, and is likewise useful in understanding the current in biological membranes. Driving force refers to the difference between the actual membrane potential and an ion's equilibrium potential. It is defined by the following equation:
In words, this equation says that: the ionic current (Iion) is equal to that ion's conductance (gion) multiplied by the driving force, which is represented by the difference between the membrane potential and the ion's equilibrium potential (i.e. Vm-Eion). Note that the ionic current will be zero if the membrane is impermeable (gion = 0) to the ion in question, regardless of the size of the driving force.
A related equation (which is derived from the more general equation above) determines the magnitude of an end plate current (EPC), at a given membrane potential, in the neuromuscular junction:
where EPC is the end plate current, gACh is the ionic conductance activated by acetylcholine, Vm is the membrane potential, and Erev is the reversal potential. When the membrane potential is equal to the reversal potential, Vm-Erev is equal to 0 and there is no driving force on the ions involved.
Read more about this topic: Reversal Potential
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