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The Extrinsic Muscles of the Wrist and Hand

The wrist makes larger movements, and the fingers and thumbs make many fine movements. So you have some longer muscles that run from the forearm (the extrinsic muscles) and lots of little hand and finger muscles (the intrinsic muscles).

To use your hands and fingers, you have to be able to bend your wrist. This movement is accomplished by two groups of muscles called the flexors and the extensors. The flexors are long muscles that run on the anterior part of the forearm from the elbow down to the hand. The tendons are held in place at the wrist by the palmar carpal ligament and the flexor retinaculum. The bellies of the muscles are located closer to the elbow, with the tendons running past the wrist. They help give the forearm its shape.

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  • Flexor carpi radialis: This wrist muscle originates on the medial epicondyle of the humerus and inserts on the base of the second and third metacarpals. It’s innervated by the median nerve and flexes and abducts the hand at the wrist.

  • Palmaris longus: This wrist-flexing muscle originates on the medial epicondyle of the humerus and inserts on the distal half of the flexor retinaculum. It’s innervated by the median nerve.

  • Flexor carpi ulnaris: This muscle flexes and adducts the hand. It’s innervated by the ulnar nerve. It has two heads:

    • The humeral head originates at the medial epicondyle of the humerus.

    • The ulnar head originates at the olecranon of the humerus. It inserts on the pisiform, hook of the hamate, and the fifth metacarpal.

  • Flexor digitorum superficialis: This muscle also has two heads:

    • The humeroulnar head originates at the medial epicondyle of the humerus and the coronoid process of the ulna.

    • The radial head originates at the oblique line of the radius.

      The flexor digitorum superficialis inserts on the bodies of the middle phalanges of the fingers, but not the thumb. It’s innervated by the median nerve, and it flexes the proximal interphalangeal joints and flexes the proximal phalanges at the metacarpophalangeal joints.

  • Flexor digitorum profundus: This muscle originates at a large part of the proximal and anterior surface of the ulna and the interosseous membrane and inserts at the bases of the distal phalanges of the fingers, but not the thumb. It flexes the distal interphalangeal joints and helps flex the wrist. It’s innervated by both the median nerve on the lateral side and the ulnar nerve on the medial side.

  • Flexor pollicis longus: This thumb muscle originates at the anterior surface of the radius and interosseus membrane and attaches to the base of the distal phalanx of the thumb. It’s innervated by the anterior interosseus branch of the median nerve and flexes the thumb.

  • Pronator quadratus: This muscle originates on the anterior shaft of the ulna and inserts on the front of the radius. It’s innervated by the median nerve, and it pronates the forearm to turn the palm from facing anterior to facing posterior.

The extensors run down the posterior portion of the forearm. As with the wrist flexors, the bellies of the muscles are on the forearm and the tendons pass through the wrist and attach to the hand. They’re held in place by the extensor retinaculum. The extensors are innervated by the radial nerve.

  • Extensor carpi radialis longus: This muscle originates on the lateral supraepicondylar ridge of the humerus and inserts on the back of the base of the second metacarpal. It extends and abducts the hand at the wrist.

  • Extensor carpi radialis brevis: Originating on the lateral epicondyle of the humerus, this muscle inserts at the back of the base of the third metacarpal. It extends and abducts the hand at the wrist and supports a clenched fist.

  • Extensor digitorum: This muscle originates at the lateral epicondyle of the humerus and inserts at the extensor expansions of the fingers, but not the thumb. It extends the fingers at the metacarpophalangeal joints.

  • Extensor digiti minimi: This finger muscle originates at the lateral epicondyle of the humerus and inserts on the extensor expansion of the fifth digit. It extends the pinkie finger at the metacarpophalangeal joint.

  • Extensor carpi ulnaris: Originating at the lateral epicondyle of the humerus and the back of the ulna, this muscle inserts on the back of the base of the fifth metacarpal. It extends and adducts the hand at the wrist.

  • Abductor pollicis longus: This muscle originates at the back of the proximal portions of the ulna, radius, and interosseus membrane. It inserts onto the base of the first metacarpal and abducts and extends the thumb.

  • Extensor pollicis longus: This thumb muscle originates at the back and middle of the ulna and interosseous membrane. It inserts to the back of the base of the distal phalanx of the thumb and extends that phalanx at the interphalangeal joint. It also extends the metacarpophalangeal and carpometacarpal joints of the thumb.

  • Extensor pollicis brevis: Another thumb muscle, this one originates at the back of the distal radius and interosseous membrane and inserts onto the back of the base of the proximal phalanx of the thumb. It extends the proximal phalanx of the thumb at the metacarpophalangeal joint and extends the carpometacarpal joint.

  • Extensor indicis: This muscle originates at the back and distal part of the ulna and interosseus membrane and inserts onto the extensor expansion of the index finger. It extends the index finger and extends the hand at the wrist.

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