The cytoskeleton is shown in face (left) and edge views (right). The marginal band of microtubules (blue) is composed of tubulin plus associated proteins. The membrane skeleton (meshwork), which underlies the plasma membrane throughout the cell, contains actin and spectrin-family proteins and intermediate filaments (green), best documented for chicken erythrocytes, are thought to maintain the position of the nucleus (brown) and to provide mechanical strength.