In a patient with decreased sensation in the pulp of the index finger, which nerve is likely affected?

The median nerve is primarily responsible for the sensation of the palmar aspects of the thumb, index finger, middle finger, and half of the ring finger, including the pulp of the index finger. When there is decreased sensation specifically in the pulp of the index finger, it points to an issue with the median nerve, which supplies sensation to this area. This is particularly evident in conditions such as carpal tunnel syndrome, where the median nerve can become compressed, leading to numbness and tingling in the fingers.

Other nerves like the ulnar nerve, while also providing sensory innervation to parts of the hand, predominantly serve the little finger and half of the ring finger. The radial nerve does not provide sensation to the palm or the pulp but is responsible for the sensation on the back of the hand and wrist. The musculocutaneous nerve primarily innervates the muscles in the anterior compartment of the arm and has little involvement in hand sensation. Thus, the most logical and correct answer regarding decreased sensation in the pulp of the index finger is the median nerve.