What is the core of microvilli composed of?

• A. Microtubules
• B. Actin filaments
• C. Intermediate filaments
• D. Keratin

Answer: (B)

Actin filaments form the internal scaffold of each microvillus. A tight bundle of actin runs the length of the projection, cross-linked by actin-binding proteins and anchored at the base to the terminal web beneath the apical membrane. This arrangement gives microvilli their rigidity and ability to extend surface area. Microtubules are the structural elements of cilia and flagella, while intermediate filaments (like keratin) provide general cell filament support but don’t form the microvillar core. So the backbone of microvilli is an actin filament bundle.