Final answer:
Bending action in cilia is accomplished by dynein arms causing microtubules to slide, with this movement constrained by flexible nexin and radial spokes, leading to cilium bending.
Step-by-step explanation:
The bending action in cilia involves microtubules, motor proteins, and specific structural constraints. Dynein arms, which are motor proteins attached to the A tubules of the microtubule doublets in cilia, walk along the B tubules of adjacent doublets. This action would normally cause microtubules to slide past each other, but the sliding is constrained by components like flexible nexin and radial spokes, resulting in the bending of the axoneme and the cilium.
Cilia have important roles in motility, feeding, and sensation, and their coordinated beating patterns facilitate the movement of fluids and trapped particles, such as in the mucociliary escalator of the airway. In specialized cells like hair cells of the inner ear, ciliary structures known as stereocilia are responsible for transducing sound vibrations into electrical signals.