Overview
This lecture covers the anatomy of the extensor carpi ulnaris muscle, including its location, origins, insertion, nerve supply, neighboring muscles, and main actions at the wrist.
Location & Views
- The extensor carpi ulnaris runs along the posterior and medial side of the forearm toward the pinky.
- It crosses both the elbow and wrist joints, but primarily acts at the wrist.
- The muscle passes under the extensor retinaculum at the wrist.
Origin & Insertion
- The muscle has two origins: the humeral head from the lateral epicondyle of the humerus, and the ulnar head from the posterior border of the ulna via a broad aponeurosis.
- The insertion is at the base of the fifth metacarpal (pinky side, under the palm).
Neighboring Muscles & Relations
- Medial to it is the flexor carpi ulnaris.
- Lateral are the extensor digitorum and extensor digiti minimi.
- Superior is the anconeus muscle.
- All these extensor muscles pass under the extensor retinaculum.
Nerve Supply
- The extensor carpi ulnaris is innervated by the posterior interosseous nerve (a deep branch of the radial nerve), with nerve roots from C7 and C8.
- The posterior interosseous nerve emerges from the supinator muscle.
Main Actions
- Adduction (moving the wrist toward the midline of the body; ulnar deviation).
- Extension of the wrist (bending the wrist backward).
Key Terms & Definitions
- Origin — the point where a muscle attaches to a stationary bone.
- Insertion — the point where a muscle attaches to a bone it moves.
- Extensor retinaculum — a fibrous band at the wrist holding extensor tendons in place.
- Aponeurosis — a broad, flat sheet of connective tissue attaching muscle to bone or other muscles.
- Adduction — movement toward the midline of the body.
- Extension — straightening movement increasing the angle between body parts.
- Posterior interosseous nerve — a deep branch of the radial nerve supplying extensor muscles.
- Lateral epicondyle — bony prominence on the outer side of the humerus.
Action Items / Next Steps
- Review diagrams of the extensor carpi ulnaris and its neighboring muscles.
- Memorize the muscle’s origin, insertion, actions, and innervation for exams.