What is the action of the extensor carpi ulnaris?

• A. Flex carpal joints and abduct manus
• B. Extend carpal joints and adduct manus
• C. Flex elbow joint
• D. Extend elbow joint

Answer: (B)

The action of the extensor carpi ulnaris is to extend the carpal joints and adduct the manus. This muscle is located on the posterior aspect of the forearm, specifically arising from the lateral epicondyle of the humerus and inserting into the base of the fifth metacarpal. Its primary function is to extend the wrist (carpal joints) and contribute to ulnar deviation, which is the adduction of the hand towards the ulnar side (the side of the little finger). This action is particularly important for movements that require stabilization and control of the wrist during activities such as gripping or throwing.

The other choices pertain to different actions that are not related to the extensor carpi ulnaris. Flexing the carpal joints and abducting the manus is attributed to other muscles, such as the flexor carpi radialis. Flexing the elbow joint involves different muscles entirely, primarily those located in the anterior compartment of the arm. Similarly, extending the elbow joint primarily involves the triceps brachii, which is also not related to the function of the extensor carpi ulnaris.