Which nerve is responsible for the sensation on the little finger side of the arm?

The ulnar nerve is responsible for the sensation on the little finger side of the arm and hand. It primarily supplies the skin on the medial aspect of the arm and forearm and provides sensation to the little finger and half of the ring finger. This nerve plays a critical role in both sensory and motor functions, and it innervates some intrinsic muscles of the hand that facilitate fine motor skills.

In contrast, the median nerve mainly innervates the thumb, index, middle, and parts of the ring finger, providing sensation to these areas on the palmar side of the hand. The radial nerve is responsible for the sensation on the back of the hand and parts of the forearm, typically affecting the thumb and part of the index finger but not the little finger. The humeral nerve is not a primary nerve involved in the sensory or motor functions of the hand; it is not commonly recognized as a nerve in this context, making it irrelevant to this specific sensory area. Thus, the ulnar nerve is the correct choice for this question as it specifically correlates to sensation on the little finger side of the arm.