The carpal tunnel is a narrow passageway in the wrist that is made of bones on three sides and a ligament (transverse carpal ligament) across the wrist where the palm and forearm meet.

Inside the tunnel are:

• Tendons, which are strong and flexible (but not stretchable) bands of tissue that connect muscle to bone. The tendons are surrounded by membranes (synovial membranes called tendon sheaths).
• The median nerve, which controls some movement in the thumb and gives sensation to the thumb, index finger, middle finger, and half of the ring finger.