The neural and muscle cells are electrically excitable, meaning that an electric current can excite them. Acute discomfort, muscular spasms, and even cardiac arrest can result from this stimulation in human patients Electrosurgery. Voltage-gated ion channels found in the cell membranes of nerve and muscle cells are responsible for their sensitivity to electric fields. At low frequencies, the stimulation threshold does not change very substantially (so called rheobase-constant level). However, once it falls below a specific minimum, the threshold begins to rise with decreasing pulse (or cycle) duration (so called chronaxie). The sensitivity to electrical stimulation (inverse of the stimulation threshold) declines with increasing frequency in the kHz range since the chronaxie of brain cells typically ranges from 0.1 to 10 ms.
