An electric shock occurs when an electrical current passes through the human body, ranging from a mild tingling sensation to severe injury or death. One of the most bewildering aspects of an electric shock is the loss of voluntary control, which prevents a person from releasing the energized object they are touching. The involuntary muscular response is a biological defense mechanism turned against the victim, trapping them in continuous contact with the current source.
How External Current Disrupts Nerve Signals
The human body relies on finely tuned electrical impulses, known as action potentials, to transmit information through the nervous system. These signals are generated by the movement of ions across nerve cell membranes, facilitating communication between the brain, muscles, and organs. When an external electrical current enters the body, it introduces a massive, unregulated surge of electricity into this delicate system. This external current overwhelms the natural, microscopic electrical signals of the neurons, effectively scrambling the communication pathways.
Alternating current (AC) is particularly disruptive because it repetitively stimulates the nerves and muscles. This constant, high-frequency stimulation bypasses the body’s natural cycle of nerve firing and resetting. The influx of electrical energy forces the voltage-gated protein channels in the nerve cells to remain open, preventing the cell from resetting its charge. As long as the external current is flowing, the nervous system cannot transmit the controlled signals needed for normal function, including the conscious command to let go.
The Physiological Mechanism of Tetanus
The inability to release an energized object is caused by a sustained, involuntary muscle contraction known as tetanic contraction. This occurs when the muscle’s motor units are stimulated by the external current at a high frequency, causing the individual twitches to fuse into one continuous, powerful spasm. The current forces the muscles to remain contracted for the entire duration of the shock, overriding any voluntary command from the brain to relax.
The reason the hand clamps shut rather than flinging open lies in the relative strength of opposing muscle groups in the forearm. The muscles responsible for flexing the fingers (flexor muscles) are generally much stronger than the extensor muscles, which open the hand. When the external current simultaneously stimulates both the flexors and extensors, the stronger flexor muscles win the resulting tug-of-war. This unequal contraction locks the fingers around the conductor, securing a tight grip that prolongs the exposure and worsens the injury. This sustained muscle contraction can also affect the diaphragm, the muscle that controls breathing, leading to respiratory arrest.
Current Magnitude and Path Determining Severity
The danger of an electric shock is primarily determined not by voltage (electrical pressure), but by amperage (the flow of current) and the path it takes through the body. The “let-go current threshold” is the maximum amount of current an individual can tolerate and still voluntarily release the source. For an average adult male exposed to common alternating current (AC), this threshold is around 10 to 15 milliamperes (mA); currents above this level make release impossible.
The resistance of the human body, determined by skin condition, plays a large role in how much current flows. Dry skin can offer significant resistance, but if the skin is wet or broken, resistance drops dramatically, allowing much higher current flow. The path the current travels through the body dictates which vital organs are affected. A current path that passes from one hand to the other, or from a hand to a foot, is particularly dangerous because it sends the current directly through the chest cavity. This path risks disrupting the heart’s natural electrical rhythm, potentially causing ventricular fibrillation (a chaotic quivering of the heart muscle).
Immediate Safety Actions During an Electrical Emergency
If a person is immobilized by a current source, the first step is to avoid becoming a second victim. Never attempt to touch the person while they are still in contact with the electricity, as the current will pass through them to you. The priority must be to safely separate the individual from the power source.
The quickest and safest action is to immediately turn off the power at the main circuit breaker or fuse box. If the power cannot be disconnected quickly, a bystander should use a non-conductive item to push the person or the source away. Materials such as a dry wooden broomstick, a plastic floor mat, or a piece of PVC pipe are appropriate for this purpose. Once the person is free from the current, call for emergency medical services.