"The Basics of Neurobiology"

Electricity Analogy
Much of the terminology used to describe signaling in neurons is borrowed from electric circuit analysis because there are so many similarities between the two. In fact neurons can be modeled with electrical circuits quite realistically. Did you notice that I have been using the term potential or voltage to describe the difference in charges found inside versus outside a neuron's membrane?

Tthe axon is like a tiny wire carrying signals. Just like electrical signals can diffuse out of an uninsulated wire--the same is true for an axon, even though the ions can’t actually pass through the membrane (unless they have a channel), their effect can. Membranes themselves do provide some insulation to charge leakage, referred to as the membrane’s resistance (Rm). Rm can also be thought of as how difficult it is for a charge to leave the membrane. The membrane serves as a capacitor (Cm) as well. A capacitor is a device that stores charge. The axon membrane naturally binds up a certain amount of charge, which presents a problem for an AP trying to travel long distances without degradation. Another impedance to the flow of charge down the axon is the cytoplasm. Charges have a difficult time traveling through cytoplasm loaded with proteins, mitochondria, etc. This resistance to the flow of charges through the cytoplasm or axoplasm is Ri. The evolution of myelin in mammals has greatly facilitated the conduction of signals through the axon by decreasing Cm and increasing Rm, therefore more charges stay inside the axon flowing to the next node. Movement of charge is defined as current, so we can also refer to the ions moving as currents. There is a Na+ current, INa, and a K+ current, IK.

Did you see the movie the Matrix? They talk about the machines harvesting humans because the human body is a great source of energy (they've exhausted the earth's supply of natural energy sources). This is a reasonable idea. The human body is quite an energy generator.

Another part of the axon that can be described in electrical terms are the ion channels. They provide a channel across the membrane through which charge can flow, or current can pass. However, since gated channels are not always open, it can be said the channels provide resistance to the flow of ions or current. Therefore the channels are described as resistors (RNa and RK). When the channels are closed there is high resistance to the flow of ions across the membrane, when the channels are open there is low resistance. Conductance (G) is the inverse of resistance: R = 1/G, so when the channels are open and there is low resistance it can also be said that there is high conductance of those ions.

Circuits are not complete unless they make a loop.
Drawn below is a circuit representing 1 voltage-gated sodium channel and 1 voltage-gated potassium channel in a membrane: