Biological circuits

All cells have a specific complement of channels, transporters and receptors that, in part, defines their unique physiology. By definition, all cells have a membrane potential. Ohm's Law defines the relationship among membrane potential (voltage), current and resistance: V = IR. Most cells have a resting membrane potential (Vm or RMP) that is negative with respect to the extracellular fluid. Electrically excitable cells (neurons and myocytes) have a much larger RMP (-30 to -70 mV) because they have a larger number of K⁺ channels open at rest.

just like an electrical circuit (think about a flashlight), a biological circuit has 4 fundamental components:

Flashlight Component	Parameter	Cell Component
Battery	Force = Voltage (also called the electrical potential difference) measured in Volts (V)	Cell membrane
Wires	Flow (current) measured in Amperes (A)	Ion channels
Light	Resistance measured in Ohms
Switch	On/off

ion channels are responsible for:
- carrying the current in the biological circuit: movement of either cations or anions into or out of the cell (more complicated than an electrical circuit where only electrons are moving)
- providing resistance: a cell that expresses few ion channels on its surface will have a higher resistance than a cell with many ion channels
- determining whether or not flow occurs (acting as an on/off switch)

2012 Ion Channel Physiology

Biological circuits