The human body is an electrical conductor, but unlike a copper wire, it functions as an electrolytic conductor. Its ability to carry an electrical charge is based on the movement of dissolved ions within its fluids and tissues. The body’s composition, approximately 60% water, creates the perfect medium for this electrical flow. Understanding this property is important for comprehending both the body’s natural functions and its vulnerability to external electrical sources.
The Role of Ions and Water in Electrical Flow
The mechanism for electrical conduction in the human body is fundamentally ionic, not electronic. Water, which makes up the majority of the body’s mass, acts as a solvent for various salts and minerals, forming electrolytes. The charge carriers in this system are not electrons, but rather positively and negatively charged atoms called ions. Key electrolytes include sodium (Na+), potassium (K+), and chloride (Cl-) ions, which are abundant in bodily fluids and tissues. When an electrical potential is applied, these ions move toward the oppositely charged pole, constituting the flow of current and driving internal bioelectrical signals like nerve impulses and muscle contractions.
Factors Determining Resistance and Impedance
The human body’s ability to conduct electricity is highly variable and non-uniform, characterized by its electrical impedance, which measures opposition to alternating current. The body is highly resistive compared to metals; however, the internal resistance of wet, salty tissues is often low, cited around 300 ohms. The external layer of the body provides a significant barrier to current entry.
The skin, particularly the outermost layer called the stratum corneum, acts as the body’s primary electrical insulator. Dry skin can exhibit a resistance exceeding 100,000 ohms, dramatically limiting the amount of current that can enter the body. However, moisture, such as sweat or water, causes this skin resistance to drop sharply, making the body much more conductive.
Internal tissues vary greatly in conductivity based on their water and ion content. Tissues with high fluid concentrations, like muscle and blood, are relatively good conductors. Conversely, tissues with low water content, such as bone and fat, are highly resistive. This variability means the current path through the body is determined by the path of least resistance, often following highly conductive blood vessels and nerves.
Physiological Impact of Electrical Current
The flow of external electrical current through the body has significant physiological consequences because it disrupts the body’s natural electrophysiology. The nervous system and muscles rely on tiny, precise electrical impulses for communication and function. An external current can override these internal signals, leading to involuntary and sustained muscle contractions, known as tetany.
If a current passes through the chest, it can cause the respiratory muscles, including the diaphragm, to lock up, resulting in respiratory arrest. The most dangerous effect is ventricular fibrillation, where the heart’s electrical activity becomes chaotic. Currents as low as 100 milliamperes can send the heart into this uncoordinated fluttering state, rendering it ineffective at pumping blood.
The body’s resistance causes electrical energy to be dissipated as heat, a process governed by Joule heating. This thermal energy can cause severe burns, which can be both superficial and deep within the internal tissues. Deep tissue injury can occur even if the external skin damage appears minimal, often due to heating along the path of the current through nerves and blood vessels.
Medical and Diagnostic Applications
The body’s electrical conductivity is purposefully utilized in several medical and diagnostic technologies. Electrocardiography (ECG or EKG) and Electroencephalography (EEG) are common examples that measure the body’s own electrical activity. These techniques use electrodes placed on the skin to detect the weak electrical signals generated by the heart and the brain, allowing physicians to monitor organ function.
Another application is Bioelectrical Impedance Analysis (BIA), which is used to estimate body composition. BIA works by passing a low-level alternating current through the body and measuring the opposition, or impedance, it encounters. Since fat tissue has a higher resistance than lean mass (muscle and water), the measured impedance is used to calculate the percentage of body fat versus lean mass.