A cell cortex is made of actin microfilaments. It is attached to the inner face of the plasma membrane in cells where microfilaments form mesh-like structure much like a fishnet except that it can be broken and reformed. This breakage and reformation is referred to as "dynamic instability."
The cell cortex functions as a mechanical support of the plasma membrane. In animal cells, it is an actin-rich layer responsible for cell-surface movements.
In plant cells, the cell cortex is reinforced by cortical microtubules underlying the plasma membrane. The direction of these cortical microtubules determines which way the cell elongates when it grows.
