Which muscle is responsible for extension at the MCP joint of the fingers?

The muscle responsible for extension at the metacarpophalangeal (MCP) joints of the fingers is the extensor digitorum. This muscle plays a critical role in enabling hand function by facilitating the straightening of the fingers at the MCP joints. When the extensor digitorum contracts, it pulls on the tendons attached to the fingers, resulting in extension.

In contrast, other muscles listed serve different primary functions. The flexor digitorum is primarily involved in flexing the fingers at the MCP and interphalangeal joints. The extensor carpi radialis mainly contributes to wrist extension and not directly to the extension of the fingers at the MCP joints. Meanwhile, the flexor pollicis longus is dedicated to flexing the thumb, not the fingers. Thus, the extensor digitorum is uniquely positioned and specifically designed to execute extension at the MCP joints, making it the correct answer in this context.