The fingers do not contain muscles. All the muscles responsible for finger motion are instead located in the hand and forearm. This arrangement allows for both remarkable strength in gripping and the intricate dexterity needed for fine motor tasks.
The Forearm’s Role in Finger Movement
The primary muscles driving the powerful movements of the fingers, such as gripping or making a fist, reside in the forearm. These are known as extrinsic muscles. These muscles include the flexor digitorum superficialis and flexor digitorum profundus, which are responsible for bending the fingers. They also include extensor muscles on the back of the forearm that straighten the fingers.
When these forearm muscles contract, they pull on long tendons. These tendons extend from the forearm, cross the wrist, and attach to the bones within the fingers. This setup allows the relatively bulky muscles of the forearm to generate significant force, which is then transmitted efficiently to the smaller, more delicate finger bones.
The Tendon and Pulley System
Tendons are strong, fibrous cords that connect muscle to bone. These long tendons, originating in the forearm, run through the palm and into the fingers. To ensure these tendons remain close to the finger bones and move efficiently, a specialized structure called the pulley system is in place.
This pulley system consists of fibrous bands, or ligaments, holding the tendons tight against the bone. Without these pulleys, the tendons would lift away from the bones when the muscles contracted, a phenomenon known as “bowstringing,” which would significantly reduce the efficiency and power of finger movement. The system includes both annular pulleys, which are ring-shaped, and cruciate pulleys, which are cross-shaped, working together to facilitate smooth and effective finger flexion.
The Hand’s Intrinsic Muscles
While the fingers themselves do not contain muscles, the hand does house smaller, specialized intrinsic muscles. These muscles are located within the palm and between the metacarpal bones, which are the long bones of the hand. They are responsible for the finer, more intricate movements of the fingers.
Examples of intrinsic hand muscles include the lumbricals and interossei. The lumbricals originate from the flexor tendons and help flex the fingers at the knuckles while extending the middle and end joints. The interossei muscles allow for movements like spreading the fingers apart (abduction) and bringing them together (adduction). These intrinsic muscles are essential for precise control in tasks such as writing, playing musical instruments, or manipulating small objects.