<Ul> <Li> Muscle contraction </Li> <Li> Cell movement </Li> <Li> Intracellular transport / trafficking </Li> <Li> Maintenance of eukaryotic cell shape </Li> <Li> Cytokinesis </Li> <Li> Cytoplasmic streaming </Li> </Ul> <Li> Intracellular transport / trafficking </Li> <Li> Maintenance of eukaryotic cell shape </Li> <P> Intermediate filaments are a part of the cytoskeleton of many eukaryotic cells . These filaments, averaging 10 nanometers in diameter, are more stable (strongly bound) than actin filaments, and heterogeneous constituents of the cytoskeleton . Like actin filaments, they function in the maintenance of cell - shape by bearing tension (microtubules, by contrast, resist compression but can also bear tension during mitosis and during the positioning of the centrosome). Intermediate filaments organize the internal tridimensional structure of the cell, anchoring organelles and serving as structural components of the nuclear lamina . They also participate in some cell - cell and cell - matrix junctions . Nuclear lamina exist in all animals and all tissues . Some animals like the fruit fly do not have any cytoplasmic intermediate filaments . In those animals that express cytoplasmic intermediate filaments, these are tissue specific . Keratin intermediate filaments in epithelial cells provide protection for different mechanical stresses the skin may endure . They also provide protection for organs against metabolic, oxidative, and chemical stresses . Strengthening of epithelial cells with these intermediate filaments may prevent onset of apoptosis, or cell death, by reducing the probability of stress . </P>

What is the purpose of the er in a cell