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The flexor muscles in your forearm allow you to write, type, grip, drive and lift objects. Turning doorknobs, getting dressed and pushing your car door closed are actions you perform, thanks to your extensor muscles, also located in your forearm. The flexing and extending mechanics of these muscles in the forearm enable you to perform a variety of tasks, many of which you likely take for granted.
Flexor muscles bend your fingers and thumb, and bend your wrist forward. These muscles travel along the front, or palm-side, of your forearm. There are two layers of wrist and finger flexors in your forearm: superficial and deep. The superficial muscles come together and form a tendon that attaches these muscles to your upper arm bone. This tendon is located just below the pointed bone on the inside of your elbow.
Flexors: Superficial Layer
The superficial layer of flexors in your forearm contains three muscles -- flexor carpi radialis, or FCR; flexor carpi ulnaris, or FCU; and flexor digitorum superficialis, or FDS. The FCR attaches to the base of your wrist, toward the thumb-side of your hand. Powered by the median nerve, it bends your wrist forward and tilts it toward your thumb. The FCU muscle attaches to the pinky-side of the base of your wrist, and is powered by the ulnar nerve. This muscle also bends your wrist forward, but tilts it toward the pinky-side of your hand.
The FDS is one of two main muscles that bend your fingers. Its tendons travel along the front of your fingers and attach just above the middle crease of your index, middle, ring and pinky fingers. It bends the middle and bottom joints of your fingers and is powered by the median nerve.
Flexors: Deep Layer
Two flexor muscles lie deep in the front of your forearm. The flexor digitorum profundus, or FDP, and flexor pollicus longus, or FPL. Tendons from the FDP travel along your fingers and attach just above the top crease in your index, middle, ring and small fingers. This muscle bends the tip of these fingers. The median nerve powers the tendons to your index and middle fingers, while the ulnar nerve powers the tendons to your ring and small fingers. The FPL muscle bends your thumb with a tendon that attaches just above your thumb crease. This muscle is powered by the median nerve.
Extensor muscles straighten your fingers and bend your wrist backward. These muscles travel in two layers -- superficial and deep -- along the back of your forearm. The superficial extensor muscles come together and form the common extensor tendon, attaching these muscles to the pointed bone on the outside of your elbow.
Extensors: Superficial Layer
Five extensor muscles lie superficially along the back of your forearm -- extensor carpi radialis longus, or ECRL; extensor carpi radialis brevis, or ECRB; extensor digitorum communis, or EDC; extensor digiti minimi, or EDM; and extensor carpi ulnaris, or ECU. The ECRL and ECRB muscles attach to the back of your wrist, toward the thumb-side of your hand. Both muscles bend your wrist backward, tilting it toward your thumb. The ECU attaches to the pinky side of the back of your wrist. This muscle bends your wrist backward and tilts it toward your pinky. The EDC muscle straightens your fingers with tendons that travel along the back of your index, middle, ring and small fingers. The EDM is a separate muscle that also straightens your small finger. These muscles are all powered by the radial nerve.
Extensors: Deep Layer
Extensor pollicis brevis, or EPB; extensor pollicis longus, or EPL; and extensor indicis form the deep layer of extensors in your forearm. The EPB and EPL muscles straighten your thumb. The extensor indicis muscle straightens your index finger. All three muscles are powered by the radial nerve.