Tenketsu

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

Neji and Hiashi Hyuga in particular have demonstrated the ability to use Eight Trigrams Palms Heavenly Spin expelling chakra from all 361 tenketsu simultaneously in order to guard 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 Hyuga clan (and Neji independently) calculated the exact tenketsu that would be required to shut down an opponents combat ability, leaving them without the strength to even use Taijutsu let alone Ninjutsu. On the other hand this attack is not lethal as a lethal blow can be accomplished with one strike by attacking the tenketsu linked to the heart. On the other hand, if all 361 tenketsu are closed, all chakra flow in a person's body will stop, and they will die.

Other Reading

 * For the real world equivalent, see Pressure Point