Practical Biomedical Paraphernalia for the Paralyzed

I ran across this article recently about advances in paralysis treatment. http://articles.news.aol.com/news/article.adp?id=20060307074209990046&cid=911
The article is about using electronic implants to stimulate muscle movement in people with paralysis. These patients have some muscle control remaining and can use this movement to initiate the electrodes imbedded within their arms. They can even cycle through several motions that are pre-programmed into the implant. Now, they are also starting to use brain waves to control the movements.
This device is very cool but I am a bit unsure of how it works. The electrodes impart tiny amounts of charge to stimulate the muscle. Does this charge cause an action potential that flows down the t-tubules in the muscle cells? Or, does this electrical charge cause voltage-gated Ca+2 channels to open up in the cells, allowing for contraction?
Finally, I looked at another similar website, and it described the amazingly small brain waves that were measured by sensors to control implants like these. Amplifiers were used in this device, which was significant to me , because we had just learned about them in electrical engineering class.