Contraction of the terminal web causes which apical modification to contract?

• A. Microvilli
• B. Cilia
• C. Stereocilia
• D. Flagella

Answer: (A)

The terminal web is a network of actin filaments just beneath the apical membrane of absorptive epithelial cells. Microvilli are the tiny, fingerlike extensions that form the brush border and are anchored to the terminal web. When the terminal web contracts through actin–myosin interactions, it pulls on the bases of the microvilli, causing the apical projections to shorten or tighten slightly. This makes microvilli the apical modification that contracts with terminal web activity.

Cilia and flagella are driven by different structures (dynein motors on microtubules in the axoneme) and are not controlled by the terminal web. Stereocilia are similar to microvilli but are specialized and their movement isn’t dictated by terminal web contraction in typical epithelial tissues.