This contractile ring consists of actin filaments and myosin II present underneath the plasma membrane. I also have heads and tails. Their tails can bind to vesicles or organelles. The movement along actin filaments allows transport to occur. Cell crawling Movements of amoebas, migration of embryonic cells, invasion of tissues with white blood cells during infection, migration of cells during wound healing, the spread of cancer, as well as phagocytosis and extension of nerve processes involve cell movement.
Movements involved in cell crawling are extension, attachment and retraction .
Extension involves polymerization and crosslinking of actin filaments. Attachment in some cells involve formation of focal adhesion sites for actin bundles. Retraction is not well understood. All types of intermediate filament proteins have a central alfa helical rod which is flanked by amino- and carboxy terminal domains. The alfa-helical rod is crucial in filament assembly.