Voltage (V) measures the electric potential difference between two points. This potential is often described as the “pressure” that drives the flow of charged particles, or current, through a circuit. Understanding voltage is necessary for studying nearly all natural and engineered systems involving electricity. Electricity governs interactions at the microscopic level, especially within the human body. Measuring minute amounts of this electrical pressure requires a smaller unit of measurement.
Understanding the Millivolt Unit
The millivolt (\(\text{mV}\)) is a scaled-down version of the standard Volt unit. The prefix “milli” denotes one-thousandth, meaning that \(1 \text{ mV}\) equals \(0.001 \text{ V}\) or \(\frac{1}{1000}\) of a Volt. This unit is widely used in scientific and medical fields where electrical signals are extremely small.
This smaller scale is necessary because many phenomena involve minute amounts of electrical energy, making expression in full Volts cumbersome. For example, \(0.070 \text{ V}\) is more clearly communicated as \(70 \text{ mV}\). The millivolt allows scientists and clinicians to report precise, low-level electrical activity without relying on excessive decimal notation.
Measuring Biological Electrical Signals
Biological systems, from single cells to entire organs, operate using electrical signals measured in millivolts. The cell membrane maintains a constant electrical potential difference called the resting membrane potential. This potential is created by the unequal distribution of ions, such as sodium and potassium, across the membrane.
A resting membrane potential in an excitable cell, such as a neuron or muscle cell, ranges from \(-70 \text{ mV}\) to \(-90 \text{ mV}\). This negative value indicates the cell’s interior is more negatively charged than the outside environment. Specialized ion channels selectively open and close, allowing charged particles to cross the membrane and temporarily change the potential to generate an electrical impulse.
Medical diagnostic tools rely on measuring the aggregated millivolt signals from millions of cells. The Electrocardiogram (\(\text{EKG}\)), which measures the heart’s electrical activity, displays signals typically \(1\) to \(2 \text{ mV}\) in amplitude. Standard \(\text{EKG}\) calibration records \(1 \text{ mV}\) as a \(10 \text{ mm}\) deflection, making these small voltages visible for clinical analysis.
The Electroencephalogram (\(\text{EEG}\)) records the electrical activity of the brain, a signal often measured in microvolts, a unit smaller than the millivolt. These large-scale measurements are a collective reflection of countless individual cells generating millivolt-level electrical potentials. The millivolt links the microscopic activity of a single cell to the macroscopic electrical rhythms measured in a clinical setting.