CILIA AND FLAGELLA

     

Cilia and flagella are hair like projections on the surface of cell. The internal structure of both cilia and flagella is same but they differ in size,number and pattern of movement. Cilia are smaller in size,numerous in number and beat perpendicularly in metachronous(cilia of row beating one after the other) or in synchronous rythm(all cilia of a row beating simultaneously). Flagella are large in size,few in number and exhibit undulating motion and beat independently

STRUCTURE OF CILIA AND FLAGELLA:

Cilia and flagella share a common ultrastructure. Cilia and flagella consist of longitudenal AXONEMA. The axonema is enclosed by spiral sheath of cytoplasm and a plasma. The cell membrane of the axonema continuos with the cell membrane of the organism. Axonema is made up of 11 longitudenal microtubules or microfibrils. Nine are peripheral and arranged in a ring. In the centre of a ring two single microtubule found which are enclosed in CENTRAL SHEATH or INNER SHEATH. There is a bridge connecting two central microfibrils
                     Each peripheral microfibril composed of two subfibres forming doublet. The inner subfibre of the doublet is complete(A tubule) and the outer subfibre is C shaped(B tubule). Each inner subfibre has two arms outer dynein arm are inner dynein arm. The arms are composed of dynein protein. A radial spoke extend from A tubule to inner sheath. Each cilia and flagella originate from their basal bodies embedded in the cytoplasm:

MOVEMENT OF CILIA:

The movement of cilia is due to sliding of double fibrils in two group one after the other. Five out of nine double fibril contract simultaneously. As a result cilium bend. This is called EFFECTIVE STROKE. Four out of nine double fibril contract as a result cilium straight. This is called RECOVERY STROKE

MOVEMENT OF FLAGELLA:

A flagellum causes movement by the passage of rapid successive wave of bending from the attached to free end, as it can be seen in flagellar movement of human sperms, which propel them forward within the fluid medium of female reproductive tract