Movements of Cilia and Flagella

1. Regulation of ciliary movement. Ciliary movement is independent of the nervous system. This is evidenced by the fact that if ciliated epithelium is removed from the organism, the cilia continue to move rhythmically. Cystoplasmic continuity is, however, essential for coordinated movement of cilia. If a piece of ciliated epithelium is cut into two, three is no coordination of ciliary movement in the two pieces. It has been proposed that rhythmic movement of cilia takes place in two steps, intraciliary excitation and interciliary conduction.

2. Contractile units of the flagellum are distributed throughout its lengths. Flagella were broken into pieces by irradiation with a laser microbeam. It was found that the pieces were able to initiate and propagate contraction for up to ten cycles. This demonstrates that the contractile units of the flagellum are distributed throughout the length of the flagellum. This fact is borne out by the observation that the amplitude of the wave of contraction does not decrease as it approaches the tip of the flagellum.

3. Plane of ciliary movement. In Opalina the bending movements of the cilia occur perpendicularly to the central tubule plane.

4. Types of movements. Movements of cilia and flagella are of four types: pendulous, unciform, infundibuliform and undulant.

(i) Pendulous movement. The cilium moves in one plane. It is flexed at its base and remains rigid during motion. This type of movements is found in the ciliate Protozoa, e.g. Paramecium.



(ii) Unciform movement also takes place in one plane. The cilium bends into the shape of a hook during contraction.

(iii) Infundibuliform movement. The cilium or flagellum rotates at its base and moves in different planes, describing a funnel, shaped figure.

(iv) Undulant movement. The waves of contraction start from the base and move to the tip.

5. Molecular mechanism. There are two main theories regarding movement of cilia and flagella. These are called the localized contraction and the sliding filament models. These are called the localized contraction and the sliding filament models.

1. The localized contraction model. Bending takes place by means of contractile units arranged at regular intervals along the length of the axoneme. The theory supposes that there is a change in the length of the subfibres of the doublets during ciliary movements.

2. The sliding filament model. According to this theory, bending of the cilium is initiated by sliding of the tubules of the peripheral fibrils relative to one another. This theory is analogous to the mechanism of muscle contraction.

6. Role of the central tubules.  It has been shown that the 9 peripheral fibrils are involved in ciliary movement. In Chlamydomonas the central tubules are absent in some mutants. Such mutatnts are non-motile. The suppressed mutants have both functional and non-functional flagella. This suggests that the central tubules are essential for flagellar contraction. It has, however, been suggested that the role of the central tubules could be the initiation and regulation of flagellar beat rather than contraction itself.