On the old "Star Trek" series, Captain Kirk and his crew never left the ship without their trusty phasers. One of the coolest things about these weapons was the stun setting.

We're still a ways off from this futuristic weaponry, but millions of police officers, soldiers and ordinary citizens do carry real-life stun weapons to protect against personal attacks.

We tend to think of electricity as a harmful force to our bodies. If lightning strikes you or you stick your finger in an electrical outlet, the current can maim or even kill you. But in smaller doses, electricity is harmless. In fact, it's one of the most essential elements in your body. You need electricity to do just about anything.

When you want to make a sandwich, for example, your brain sends electricity down a nerve cell, toward the muscles in your arm. The electrical signal tells the nerve cell to release a neurotransmitter, which is a communication chemical, to the muscle cells. Neurotransmitters tell the muscles to contract or expand in just the right way to put your sandwich together. When you pick up the sandwich, the sensitive nerve cells in your hand send an electrical message to the brain, telling you what the sandwich feels like. When you bite into it, your mouth sends signals to your brain telling you how it tastes.

­In this way, the different parts of your body use electricity to communicate with one another. This is actually a lot like a telephone system or the Internet. Specific patterns of electricity are transmitted to deliver recognizable messages.

See the next page to learn more about how a stun gun confuses the nervous system.