he Short Answer: The cells of all living things generate electrical charges. In an electric eel (Electrophorus electricus), thousands of modified muscle cells in the thick tail are lined up like batteries in a flashlight. Though each cell generates only about 0.15 volts, in a large electric eel, six thousand cells may be stacked to make one giant battery that can generate as much as 600 volts for a short pulse. A standard car battery generates 12 volts, so an electric eel has 50 times the shocking power of a car battery (though with less amperage).
How electrocyte cells produce electricity: As I mentioned above, every cell generates tiny electrical charges. This is done primarily by moving various positive ions (charged atoms or molecules) of metals such as sodium, potassium, and calcium out of the cell, which makes the outside of the cell positive compared to the inside of the cell. These ions might move back into the cell to equalize the charge difference, but cells use chemical energy to continually “pump” the ions out of the cell. This is all part of normal cell chemistry. This “resting voltage” is typically about 0.085 volts. In most cells, this charge isn’t much use as a battery, however, because it’s uniformly spread around the outside of the cell. The outside of the cell is positively charged and the inside is negatively charged. This arrangement makes impossible to stack them up to generate a high voltage. The electric eel’s electrocyte cells are different, however. They aren’t symmetrical. They have a relatively smooth side that is connected to nerve fibers, and a relatively convoluted side that is not. And all the electrocytes in a stack are oriented in the same direction, with the smooth side towards the tail and the convoluted side towards the head.
When the nerve fibers send a signal to an electrocyte, special pores on the smooth side of the cell open, allowing positive ions to rush into the cell. This temporarily creates an additional charge across the cell membrane on that side of the cell of about 0.065 volts. Now, instead of having a negative inside and a positive outside, the cell temporarily has a 0.085 volt difference across the convoluted side, and a similarly oriented charge of about 0.065 volts on the smooth side. These charges are essentially stacked in series, so that the end result is a brief charge across the entire cell of about 0.15 volts (0.085 +0.065).
But here’s the problem. This directed orientation of the charges doesn’t last long. In short order, the pores on the smooth side close, and the cell reverts back to its resting state. So if a normal nerve signal went out from the brain to each electrocyte, the signal would reach the first cells in the stack before it reached the cells at the end of the stack. By the time the cells at the end fired, the ones at the beginning would have already shut off again. Somehow, the electric eel has to synchronize the firing of thousands of electrocytes in a stack so they all turn on at the same time and add together to create the big voltage needed to shock the fish’s prey. Exactly how this works is not yet known, but it appears that at least three factors are involved:
Nerve fibers closer to the head are smaller than those near the tail.
Nerves closer to the head also tend to take a more winding path than nerves near the tail.
Slower chemical signals are used in nerve fibers closer to the head.
All of these factors tend to slow nerve signals near the head and speed the ones near the tail. This equalizes the arrival of the signal, and allows all the electrocytes in a stack to fire at the same time.