The anterior interosseous nerve innervates how many muscles?

The anterior interosseous nerve innervates 2.5 muscles in the forearm. It is a branch of the median nerve and specifically innervates the flexor pollicis longus and the lateral half of the flexor digitorum profundus. The reference to "0.5" muscle indicates that it partially innervates the flexor digitorum profundus, as it only supplies the lateral part, which corresponds to the index finger.

It’s important to understand the anatomy: the flexor pollicis longus is fully innervated by the anterior interosseous nerve, while the flexor digitorum profundus is only partially innervated (the lateral half). The pronator quadratus is also innervated by the anterior interosseous nerve, but it is often considered separate due to its different functional role, which is likely where the term "2.5 muscles" arises from.

This nuanced understanding of the anterior interosseous nerve's innervation highlights the complexity of muscular innervation in the forearm and emphasizes the significance of the nerve's role in fine motor control.