Nerve ending
Nerve endings were parts of the nervous system which sent messages to the brain when one felt sensations such as pain.

In 2268, Spock's brain was surgically removed yet  he remained alive. According to Doctor Leonard McCoy, it was the greatest technical job he had ever seen. Every nerve ending in the brain had been neatly sealed; nothing ripped nor torn, and no bleeding, which he considered a medical miracle. Later while re-inserting Spock's brain, McCoy used a sonic separator to stimulate Spock's nerve endings and he observed the physical reactions one by one. ()

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Anatomy