Filopodia (singular filopodium) are action-rich bulbous-shaped protrusions that function like antennae for a cell to probe the surrounding extracellular environment. They are 60-200 nm in diameter made of parallel bundles of 10-20 actin filaments. Filopodia are classified as pseudopodia (temporary protrusions and retractions of the cytoplasm of eukaryote cells). As such, they have a simpler molecular structure than cilia and flagella, and unlike them have an amoeboid movement. The initiation and elongation of filopodia are dependent on the regulation of polymerizartion, and the convergence of cross-connections among these filaments. Typically, they are embedded within or protruding from the lamilliopodia situated at the front of migratory cells, thus serving a crucial role in cell locomotion and migration. They are also evident in neurite growth cones and cells such as fibroblasts. During development, but before the emergence of dendritic spines, cortical dendrites exhibit very long, thin processes often without a filapodium. As the cortex develops, the dendritic filapodia, distinct from other filapodia, disappear and spines emerge.
See Actin, Cell locomotion, Cell migration, Cilia, Dendrite, Extracellular matrix, Fibroblasts, Flagella, Growth cone, Lamillipodia, Neurite, Polymerization, Quantitative and qualitative regressions