Tonofibrils

Strings of several different filament networks span the cytoplasmic matrix of cells to form the cytoskeleton. These networks are a dynamic system. There are three distinct networks with morphologically different structures:  microfilaments, intermediary filaments and microtubules. Among others, there are desmin, vimentin and spectrin filaments, also neurofilament in neurons, glial filaments in glial cells and keratin filaments in epidermal epithelium. Each of these network s is built from specific proteins. As a group, they are sometimes still referred to as “ metaplasmic” structures—a name that was coined in the era of light microscopy. The tonofibrils (resistance fibrils) of ten serve as a well-known demonstration example of a fiber network . Tonofibrils are particularly impressive in cells from multilayered squamous epithelium

in mechanically resilient tissue. These tonofibrils are dense bundles of intermediary protein filaments (cytokeratin filaments ) of undefined lengths  and can be seen using a light microscope. Intermediary filaments have diameters of 8–10 nm. This figure shows tonofibrils in flat squamous epithelial cells from bovine hoof.

References

Kuehnel, W.(2003). Color Atlas of Cytology, Histology, and Microscopic Anatomy. 4^th edition . Institute of Anatomy Universitätzu Luebeck Luebeck, Germany . Thieme Stuttgar t · New York .