Carpal tunnel

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.

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