Which nerve root is primarily responsible for finger abduction?

The nerve root primarily responsible for finger abduction is T1. This is because the T1 nerve root contributes to the function of the ulnar nerve, which innervates the intrinsic muscles of the hand, particularly the interossei muscles. These muscles are critical for the abduction and adduction of the fingers.

When the interossei muscles contract, they facilitate movements such as spreading the fingers apart (abduction) and bringing them together (adduction). Since finger abduction specifically relies on the proper functioning of these muscles, the T1 nerve root is crucial for this action.

Other nerve roots mentioned do have motor functions in the arm and hand but do not specifically govern finger abduction. For instance, C8 primarily innervates the muscles involved in finger flexion and is more involved in grasping movements, while C7 has a role in wrist and finger extension. S1 is associated with functions in the lower extremities, having no direct impact on finger movement. Thus, T1's direct association with the intrinsic muscles of the hand highlights its importance in finger abduction.