Which function do the lumbricals serve in finger movement?

The lumbricals play a critical role in the intricate movements of the fingers, particularly in facilitating the flexion and extension of the digits at the metacarpophalangeal (MCP) joints and the interphalangeal (IP) joints. Specifically, the primary function of the lumbrical muscles is to enable flexion at the MCP joints while simultaneously allowing for extension at the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints. This is crucial for precision grip and manipulating objects, as it allows the fingers to flex at their base while maintaining extension of the middle and distal segments, providing both stability and dexterity.

In contrast, the other options do not accurately describe this coordinated movement. For example, while some options suggest flexion and extension at various joints, they either misplace the flexion or extension or suggest actions that the lumbricals do not perform with respect to specific joints. Thus, option B accurately encapsulates the functional role of the lumbrical muscles in the coordination of finger movements during grasping and manipulation tasks.