Cilia and flagella
The flagella have the function of allowing the movement of the cell, and the cilia, creating turbulence near the cell to bring food closer together.
- The cilia are short and very numerous, covering the cell surface. Its movement is coordinated from back to front.
- The flagella are long and few, generally only 1 or 2. Their movement is wave-like.
Cilia and flagella are made up of:
- The stem or axoneme. Surrounded by the plasma membrane and has inside:
- Two central microtubules surrounded by a thin nexin sheath .
- 9 pairs (doublets) of peripheral microtubules surrounding the central pair. In each pair, it is distinguished:
- Microtubule A: complete, with 13 protofilaments. From this microtubule, two arms of the protein dynein emerge towards the microtubule B of the neighboring pair.
- Microtubule B: with 10 protofilaments, it shares 3 with A.
This arrangement is called 9 + 2. The microtubule pairs are linked by nexin. Other nexin fibers link each A microtubule to the central sheath.
- Transition zone. It is the area where the change occurs between the structure (9 + 2) of the stem or axoneme with the structure (9 + 0) of the basal body or centriole. The two central microtubules disappear, and the peripheral doublets become triplets.
- The basal corpuscle is a cylinder located at the base of the cilium or flagellum, below the plasma membrane. It has the same structure as the centrioles (9 + 0), since it lacks the central microtubule pair, and has 9 peripheral microtubule triplets.
- Ciliary roots (not always present). They are microfilaments that emerge from the lower end of the basal corpuscle, with a contractile function, which coordinates the movement of the cilia.