The “Mother of Fingers” is a colloquial term for the ulnar nerve, which runs along the inside (or little finger side) of the forearm and into the hand. It provides sensation to the little finger and the inner half of the ring finger, as well as controlling some of the small muscles in the hand.
The ulnar nerve is important for fine motor skills, such as writing, playing musical instruments, and buttoning clothes. Damage to the ulnar nerve can cause weakness or numbness in the hand, and can make it difficult to perform these tasks.