Fibre Ultrastructure.

Mammalian hair fibres can be structurally divided into three main components: a cuticle, cortex and sometimes a medulla. The cuticle consists of a thin layer of overlapping cells on the surface of the fibre, constituting around 10% of the total fibre weight. The cortex makes up the remaining 86-90% and is made up of axially aligned spindle-shaped cells of which three major types have been recognised in wool: ortho, meso and para. Cortical cells are packed full of macrofibril bundles, which are a composite of aligned intermediate filaments embedded in an amorphous matrix. The spacing and three-dimensional arrangement of the intermediate filaments vary with cell type. The medulla consists of a continuous or discontinuous column of horizontal spaces in the centre of the cortex that becomes more prevalent as the fibre diameter increases.