What type of filament does NOT form part of the cytoskeleton?

Myofibrils do not form part of the cytoskeleton. They are specialized structures found in muscle cells and are primarily responsible for muscle contraction. Myofibrils are composed of repeating units called sarcomeres, which contain the essential proteins actin and myosin that facilitate contraction.

In contrast, the cytoskeleton is comprised of three main types of filaments: microtubules, microfilaments, and intermediate filaments. Microtubules provide structural support and are involved in intracellular transport, the organization of the cell, and cell division. Microfilaments, also known as actin filaments, are involved in cell shape, motility, and muscle contraction. Intermediate filaments provide tensile strength and help maintain cell integrity. Thus, myofibrils, while crucial to muscle function, are separate from the cytoskeletal framework that supports cellular structure and dynamics.