Structure of a cilium - colour-enhanced

Cilia and flagella both have this structure - an axoneme surrounded by cell membrane. At their core is a circular arrangement of nine pairs of microtubules around a single pair in the centre, known as the axoneme. This is commonly called the 9 + 2 arrangement. Each peripheral pair has one complete microtubule and one nearly complete microtubule. Several other proteins are associated with the microtubules and either hold the axoneme together or control the sliding of the paired microtubules past each other. This sliding causes the bending movements of the cilla.