Chakra Pathway System

The is a term used to describe the points within the body that channel chakra through it. Simply put they serve the same function for chakra as blood vessels do for blood. Along the chakra pathways, there are 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.

Overview
The chakra pathway system is enmeshed within the body, transporting chakra through the body and each organ as the circulatory system does blood. The system is in some way involved in the creation of chakra itself as well, as every cell in the body is connected to this pathway system by a capillary which draws out the cell's physical energy and is refined into chakra by several organs, such as the heart. If the chakra flow to a section of the body is blocked by such techniques as Gentle Fist or Bloody Mist Sword Art: Bone Mutilation, then that portion of the body will be unable to release any chakra from any of the tenketsu. Neji Hyūga was shocked that Naruto Uzumaki 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 Hyūga clan's Gentle Fist fighting style which forces chakra into an opponent's chakra pathway system. 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.

Though Neji and more advanced users are known for attacking tenketsu, basic Gentle Fist is also extremely powerful as the chakra forced into the chakra pathways need not be specific as it affects everything in its vicinity. By using Gentle Fist, Neji was able to damage Hinata's heart and the surrounding area to the extent that she was still not fully recuperated a month later.

Naruto's Wind Release: Rasenshuriken destroys the chakra pathway system by severing every cell's connection to it, preventing the target - and to a lesser extent, the arm that used the jutsu - from creating chakra. The damage inflicted cannot be repaired with any medical ninjutsu whatsoever, which not only crippled the enemy permanently, but also threatened to destroy Naruto's ability to mould chakra if he repeatedly use the technique as it was then. Naruto would eventually overcome this weakness by learning to throw the Rasenshuriken.

Trivia

 * The heart is implied to be especially important for chakra production in this system. The organ is shown when the chakra pathway system is first explained, and:
 * Taking the hearts of other shinobi allows Kakuzu to gain both their chakra and elemental affinity as his own. This lets him produce high-level jutsu of any basic nature, something that isn't ordinarily possible.
 * The heart is also the location of the Eighth Gate, the opening of which unleashes the user's entire chakra capacity and results in their death.