Forearm Muscles: Anatomy, Support & Movement

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  • 0:05 Muscles That Move the…
  • 1:06 Muscles That Flex the Hand
  • 2:17 Muscles That Extend the Hand
  • 3:30 Muscles That Move the…
  • 5:48 Lesson Summary
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Lesson Transcript
Instructor: John Simmons

John has taught college science courses face-to-face and online since 1994 and has a doctorate in physiology.

Did you know the muscles that move the hand, fingers and thumb are located in the forearm? This lesson identifies and describes the major muscles that flex and extend the wrist, fingers and thumb.

Muscles that Move the Hand and Fingers

Whether you are playing a video game or catch in the back yard, you need to coordinate the movement of your wrist, hands and fingers. Most muscles that move the hand and fingers are located in the forearm and are innervated by the median nerve. The median nerve, along with forearm muscle tendons, travels through the wrist under the carpal ligament, a.k.a. flexor retinaculum, which stabilizes the tendons of these muscles. We become painfully aware of this anatomical relationship with injuries such as carpal tunnel syndrome, in which inflammation of the tendons compresses the median nerve.

This lesson will describe the muscles that move the hand, fingers and thumb. We will organize our discussion based on common functions as we examine muscles that flex the hand at the wrist, muscles that extend the hand at the wrist, and muscles that move the fingers and thumb.

Muscles that Flex the Hand

Let's start by examining the muscles that flex the hand at the wrist. These are long muscles that run along the anterior part of the forearm from the elbow to the hand. At the elbow, they originate from the medial side of the humerus. The distal tendons are held in place at the wrist by the flexor retinaculum (as discussed previously in the context of carpal tunnel syndrome). You can actually feel these tendons. Make a ball with your hand and you can actually see the tendons.

One of many muscles that flex the wrist.
Flexor Carpi Ulnaris

The flexor carpi radialis is so named because it courses over the radius and inserts on the wrist bones. Likewise, the flexor capri ulnaris courses over the ulna (in the forearm) and inserts on the wrist bones. The palmaris longus runs between the flexor carpi ulnaris and radius and inserts on the flexor retinaculum, not the bones. Pitchers can have problems with these muscles as they forcibly flex the wrist just as they release the baseball.

Muscles that Extend the Hand

The three muscles that work to extend the hand.
Extensor Hand Muscles

The muscles that extend the hand at the wrist are located on the posterior portion of the forearm. The tendons of the hand extensor muscles pass under the extensor retinaculum and attach to the hand (similar to the flexor retinaculum on the anterior side of the wrist). These muscles have names similar to the flexors as they course over the radius and ulna in the forearm. Let's take a look at them.

The extensor carpi radialis longus and extensor carpi radialis brevis originate from the humerus, course over the radius, and insert on the hand. As the name suggests, the longus is longer than the brevis (like 'brief'). The extensor carpi ulnaris originates from the humerus and ulna, courses over the ulna, and inserts on the hand. While both of these muscles cause extension of the hand, the radialis muscles cause abduction, while the ulnaris causes adduction of the hand. If you consider the relative attachments of these muscles, it makes sense.

Muscles that Move the Finger and Thumb

Most muscles that move the fingers are located in the forearm. They are attached to the phalanges, or finger (or digit) bones, via long tendons, and they operate much like a puppet on strings.

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