It is quite easy to think of cytoplasm as a disorganised, jelly-like sub-store. The truth is that surrounding the classic membrane-bound structures and organelles, the cytoplasm contains the cytoskeleton.

The cytoskeleton is a cytoplasmic scaffolding system comprising both “muscle” and “skeletal” properties unique to eukaryotic cells. Its main responsibility is the mechanical and spatial interaction of cells within their environment. The cytoskeleton enables structural changes to take place within cells as they grow, divide and adapt to the environment. It gives the cell strength and rigidity and ultimately maintains cell shape by organising organelles within the cell. It also allows for movement (cytokinesis) of cells from one place to another as well as the movement of intracellular components and organelles.

The cytoskeleton is mainly composed of 3 kinds of protein filament systems – microfilaments (4-7nm in diameter – built up of the protein actin), intermediate filaments (approximately 10nm in diameter – built up of one or more rod-shaped protein subunits) and microtubules (approximately 24nm in diameter – polymers of the protein tubulin). All have specific associated proteins and interact with each other in a variety of ways as well as sharing common properties.

The cytoskeleton is responsible for all movement within cells and the detection of signals from the cell's surrounding environment. Other functions include:

	The separation of chromosomes during mitosis (cell division) and consequent splitting of the mitotic cell.
	The intracellular trafficking of materials and organelles from one part of the cell to another.
	Support of the plasma membrane, especially during environmental changes where the cell is able to tolerate stresses and strains without bearing any damage.
	It enables sperm to swim and cells such as fibroblasts and white blood cells to adhere and spread across surfaces.
	It allows muscle cells to contract and neurons to extend.
	It also directs the growth of the plant cell wall and cell shape diversification in eukaryotes.

The cytoskeleton is also involved in processes such as cell secretion, signal transduction, cell adhesion, oncogenesis (cancer development) and apoptosis (programmed cell death), lymphocyte activation, the inflammatory response, cell cycle control and growth control.

In short, the cytoskeleton is responsible for all of the functional properties of living cells. The way in which its functional components work is the same in all eukaryotic cells. As such, it is clearly a fundamental part of all living cells.