Intermediate filaments

macromolecular protein polymers that are involved in determining the shape of cells.

They are of a size intermediate between microfilaments and microtubules.

There are several different types of intermediate filaments, such as keratin in epitherlial cells, desmin in muscle cells, neurofilaments in axons and vimentin in fibroblast cells, that are composed of different protein subunits

Intermediate filaments are involved in determining the shape of red blood cells

When RBCs are placed in a hyperosmotic solution water leaves the cell by osmosis. The RBCs form an angular shape because the plasma membrane collapses but the cytoskeleton retains its shape.

When RBCs are placed in a hypoosmotic solution was enters the cell and the plasma membrane eventually burts. Structures called "ghosts" remain. These structures are composed of the plasma membrane and associated cytoskeletal elements such as intermediate filaments.