Chakra Pathway System

is the term for the pathways within the body that transfer and channel chakra. Simply put they serve the same function for chakra as blood vessels do for blood. Along the Keirakukei there 361 nodes called Tenketsu that control the flow of chakra like circuit breakers, and within those Tenketsu are Eight Gates which control body function and strain levels. The Keirakukei as the literal meaning implies is enmeshed into the body and like blood vessels it touches and interacts with every single living cell and passes through every organ. If the chakra flow to a section of the body is severed then that portion of the body will generally become numb and useless. As Neji was shocked that Naruto was still able to stand after being hit with Eight Trigrams Sixty-Four Palms as his body should have been in a virtually quadriplegic state.

Understanding this system is the key to the Hyuga Clan's Juken fighting style which forces chakra into an opponent's keirakukei. Proper application uses the system as a conductor sending harmful chakra directly to vulnerable vital organs. As there is no way to train a person's organs to resist physical or energy attack this method of fighting is extremely effective. An analogy could me made to being attacked with a tazer. Though Neji and more advanced users are known for attacking tenketsu basic juken is also extremely powerful as the chakra forced into the keirakukei need not be specific as it effects everything in its vicinity. By using Juken Neji was able to damage Hinata's heart to the extent that she was still coughing up blood a month later.

Other Reading

 * For the real-world equivalent see Channels.