The cell cortex is a peripheral layer of cytoplasm beneath the cell membrane, containing the actomyosin ring during typical animal cytokinesis.
Its actin-rich network helps set surface mechanics and couples membrane motion to contractile forces. Local changes in attachment or assembly can produce a membrane bleb, while coordinated actomyosin activity can support constriction or migration. [ref]
Molecular Biology of the Cell, 4th edition by Bruce Alberts and others. Chapter 16, The Cytoskeleton: actin cortex
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