Cell: Structure and Function - Cytoskeleton, Cilia, Flagella, and Centrioles

The Cytoskeleton is an elaborate network of proteinaceous filaments present in the cytoplasm, consisting of microfilaments (actin), microtubules (tubulin), and intermediate filaments.

Functions of the Cytoskeleton include providing mechanical support, motility, and maintenance of the shape of the cell.

Cilia and Flagella are hair-like outgrowths of the cell membrane. Cilia are small structures that work like oars, causing movement of either the cell or the surrounding fluid, while Flagella are comparatively longer and responsible for cell movement.

The Axoneme is the core of the cilium or flagellum, possessing a $9 + 2$ array of microtubules: nine pairs (doublets) of radially arranged peripheral microtubules and one pair of centrally located microtubules.

The Central tubules in an axoneme are connected by bridges and enclosed by a central sheath, which is connected to one of the tubules of each peripheral doublet by a radial spoke, resulting in $9$ radial spokes.

Centrosome is an organelle containing two cylindrical structures called centrioles, which lie perpendicular to each other and are surrounded by amorphous pericentriolar materials.

Centrioles have an organization like a cartwheel, consisting of nine evenly spaced peripheral triplets of tubulin protein, following a $9 + 0$ arrangement with no central microtubules.

Centrioles form the basal body of cilia or flagella and the spindle fibers that give rise to the spindle apparatus during cell division in animal cells.