Final answer:
The extensor carpi ulnaris muscle originates from the lateral epicondyle of the humerus, the posterior border of the ulna, and the intermuscular septa. It inserts into the base of the fifth metacarpal and its action is to extend and adduct the hand at the wrist.
Step-by-step explanation:
The extensor carpi ulnaris is a skeletal muscle located in the forearm. It has its origin at the lateral epicondyle of the humerus, posterior border of the ulna, and the intermuscular septa. It inserts into the base of the fifth metacarpal. The primary action of the extensor carpi ulnaris is to extend and adduct the hand at the wrist.
Other muscles that also participate in extending and manipulating the wrist and fingers include the extensor digitorum, which extends the hand at the wrist and the phalanges, and the extensor digiti minimi, which is responsible for extending the little finger, among others. Muscles like the extensor digitorum longus and extensor digitorum brevis are involved in extending the toes.