Tenketsu

are simply nodes from which chakra can be released. There are 361 tenketsu in the body, each one being a checkpoint on the Chakra Pathway System. Though ninja use chakra regularly, very few ninja possess any great control over their tenketsu. Even of jōnin, the vast majority are only capable of releasing a small amount of chakra through their hands or feet to increase the power of punches, jumps, or kicks. For the Hyūga clan, whose entire fighting style is based around manipulating the chakra pathway system, controlling the tenketsu is a regular matter.

Neji and Hiashi Hyūga in particular have demonstrated the ability to use Eight Trigrams Palms Revolving Heaven, expelling chakra from all 361 tenketsu simultaneously in order to guard against and repel enemy attacks. The Eight Trigrams Sixty-Four Palms closes sixty-four tenketsu. Though not explicitly stated, it is logical to say that the Hyūga clan (and Neji independently) calculated the exact tenketsu that would be required to shut down an opponent's combat ability, leaving them without the strength to even use taijutsu, let alone ninjutsu. This attack, however, is not lethal, though a lethal blow can be accomplished with one strike by attacking the tenketsu linked to the heart, or by attacking all 361 tenketsu, though the one strike to the heart would be much more efficient.

Other Reading

 * For the real world equivalent, see pressure point.