Which nerve's distribution is primarily affected in carpal tunnel syndrome?

Carpal tunnel syndrome primarily affects the median nerve because this nerve runs through the carpal tunnel, a narrow passageway in the wrist. The median nerve is responsible for sensory innervation to the palmar side of the thumb, index, middle, and part of the ring fingers, as well as motor innervation to some hand muscles. When the structures within the carpal tunnel, such as the flexor tendons or the surrounding tissues, become swollen or inflamed, they can exert pressure on the median nerve, leading to symptoms such as pain, numbness, and weakness in the affected areas. This is a key feature of carpal tunnel syndrome, making it essential to understand the anatomical and physiological role of the median nerve in this condition. The other nerves listed do not pass through the carpal tunnel and thus are not primarily affected in this syndrome.