Which of these actions is associated with the function of the splenius capitis?

The splenius capitis is a muscle located in the back of the neck that plays a crucial role in head movement. Its primary function is to facilitate the extension of the head and neck. When the splenius capitis contracts, it pulls the head backward, allowing for extension at the atlantooccipital and cervical joints.

In addition to extension, the splenius capitis also assists in lateral flexion and rotation of the head to the same side. However, when considering the primary action associated with this muscle, extension is the most significant.

The other options presented are less relevant to the primary function of the splenius capitis. Flexion refers to bending movements that decrease the angle between body parts; adduction involves moving a limb toward the midline of the body; and abduction is the movement away from the midline. These actions do not accurately describe the primary role of the splenius capitis in neck and head movement.