The Vulcan nerve pinch was a martial technique developed by the Vulcans. Likely related to neuropressure, it involved applying pressure near the base of the neck, at the shoulder, and nearly instantly rendered the target unconscious, often so fast that the target was unable to cry out, but not always. (TOS: "Day of the Dove")
The technique did not appear to cause permanent injury and seemed to be effective on most humanoid species. The only Human to have ever been insensitive to it was Gary Seven, possibly because of metabolic alterations obtained on his planet of adoption. (TOS: "Assignment: Earth") When used on Human Augments like Khan Noonien Singh, it caused pain but was not enough to subdue them. (Star Trek Into Darkness) It was proven ineffective on robotic androids when Spock took the time to softly try it on android Alice, who simply asked him calmly if that gesture had any significance. (TOS: "I, Mudd") Vians are unaffected by the nerve pinch.
Spock once performed the Vulcan nerve pinch on a horse, Selek did one to a Le-matya, and Tuvok once did it to a member of Species 8472 that had disguised itself as a Human. (Star Trek V: The Final Frontier; TAS: "Yesteryear"; VOY: "In the Flesh") Spock was also known to use a two-handed variety of the technique to subdue two opponents. (TOS: "Whom Gods Destroy")
Use by non-Vulcans
On some occasions non-Vulcans have been instructed in the technique. Spock has attempted in vain to teach Kirk. On planet Omega IV, while fighting Cloud William and Sirah in his cell, Kirk expressed his appreciation for the neutralization of Sirah by Spock with the pinch. (TOS: "The Omega Glory") Overall, the nerve pinch seemed to be extremely difficult to learn for non-Vulcans, although the android Data was able to master it, (TNG: "Unification II") as was Jean-Luc Picard, years after his mind meld with Sarek. (TNG: "Starship Mine", Star Trek Nemesis) Jonathan Archer was also able to perform the nerve pinch while carrying the katra of Surak. (ENT: "Kir'Shara") Dr. McCoy, however, was unsuccessful in performing the technique on a security officer while carrying Spock's katra, likely due to the doctor's arthritis. (Star Trek III: The Search for Spock)
The reclaimed Borg drone Seven of Nine also displayed the ability to perform it, most likely having acquired this knowledge from Vulcans assimilated when she was still part of the Borg Collective. (VOY: "The Raven")
The Vulcan nerve pinch was referred to as the "Famous Spock Nerve Pinch" or "FSNP" in the scripts of TOS. It was invented for the episode "The Enemy Within" by Leonard Nimoy, who felt that Spock was too dignified to render someone unconscious by striking them over the head. (Star Trek Encyclopedia) The first character on which it was performed was James T. Kirk.
According to Leonard Nimoy, on the "25 year mission tour" video, when he was pitching the idea for the neck pinch, the director asked about it and Nimoy said that Spock was a graduate of the Vulcan Institute of Technology where he took a number of courses on the human anatomy and that Vulcans have a kind of energy that comes off their fingertips, which when applied to certain points on the human neck, it renders the human unconscious. Nimoy said then that the director had no idea what he was talking about but then when he explained it to Shatner, he got it immediately and Nimoy credits Shatner's reaction as to what sold the idea of the neck pinch.
In the novelization of Star Trek IV: The Voyage Home, author Vonda N. McIntyre has Admiral James T. Kirk performing a Vulcan nerve pinch to stop one of the twentieth century Earth doctors, who was trying to prevent Dr. Leonard McCoy from doing the high-tech, non-invasive repair of the fallen Pavel Chekov's middle meningeal artery in the hospital scene in that movie. In the book, after Kirk successfully uses the nerve pinch he says "that never worked before, and will probably never work again."
In the Star Trek RPG, published by Last Unicorn Games, the nerve pinch is part of the martial art Taroon-Ifla, the only known martial art which consists of a single advanced technique. Presumably, Taroon-Ifla includes nearly endless variations and applications of the nerve pinch (the Taroon), making it effective on an assortment of lifeforms and includes less aggressive functions, such as healing techniques similar to acupressure.