Here's why:

* Z lines are the boundaries of a sarcomere, the functional unit of a muscle fiber.

* Actin filaments are thin filaments that extend from the Z line towards the center of the sarcomere.

* Myosin filaments, the thick filaments, are located in the center of the sarcomere and interact with the actin filaments during muscle contraction.

Therefore, the Z line serves as the anchor point for the actin filaments, which are essential for muscle contraction.