There are three types of electrical signals in human beings, two of which are routinely monitored or analyzed for diagnostic purposes. The first is the electroencephalogram, which is a relatively weak, fluctuating signal that originates in the brain. The second is the electrocardiogram, which is about 100 times stronger than the electroencephalogram, and is produced by the contractions of the heart muscle. The third type of electrical signal in humans, the surface electrical potential, is about as strong as the electrocardiogram but changes more slowly over time. The origin and significance of the surface electrical potential in humans are not yet known.
Common diseases and disorders
A large number of diseases and disorders are related to disturbances of the bioelectrical system. These conditions can be classified according to the component of the nerve cell/muscle cell group, or motor unit, that is affected. The motor unit can be divided into the motor neuron, the nerve root (paired bundles of nerves coming from the spinal cord), the nerve plexus (bundles of nerves further removed from the spinal cord), the peripheral nerve, the neuro-muscular junction, and the muscle fiber. Defects in any of these components may disrupt bioelectrical signals.