====== Cytoskeleton ======

===== Related to neurosurgery =====

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The cytoskeleton is a [[network]] of [[fiber]]s composed of [[protein]]s contained within a cell's [[cytoplasm]]. Although the name implies the cytoskeleton is stable, it is a dynamic structure, parts of which are constantly destroyed, renewed, or newly constructed.
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[[Cytoskeletal protein]].

===== Cytoskeleton Classification =====

The cytoskeleton is divided into three main types of filaments based on their size, protein composition, and function. A fourth group, **septins**, is emerging as a potential cytoskeletal element.

===== ~~CLOSE~~ Microfilaments (Actin Filaments) =====
  * **Diameter**: ~7 nm
  * **Main protein**: Actin (G-actin polymerizes into F-actin)
  * **Polarity**: Yes (plus and minus ends)
  * **Functions**:
    * Maintains cell shape
    * Cell motility (lamellipodia, filopodia)
    * Cytokinesis (contractile ring)
    * Intracellular transport (with myosin)
    * Endocytosis and exocytosis
  * **Associated proteins**: Arp2/3 complex, cofilin, profilin, myosin

===== ~~CLOSE~~ Intermediate Filaments =====
  * **Diameter**: ~10 nm
  * **Main proteins** (tissue-specific):
    * Keratins (epithelial cells)
    * Vimentin (mesenchymal cells)
    * Desmin (muscle)
    * Neurofilaments (neurons)
    * Lamins (nuclear envelope)
  * **Polarity**: No
  * **Functions**:
    * Mechanical support and structural stability
    * Anchoring organelles
    * Nuclear integrity (nuclear lamina)

===== ~~CLOSE~~ Microtubules =====
  * **Diameter**: ~25 nm
  * **Main protein**: Tubulin (α/β dimers)
  * **Polarity**: Yes
  * **Functions**:
    * Organelle and vesicle transport (kinesin, dynein)
    * Mitotic spindle formation (cell division)
    * Cilia and flagella structure
    * Cell polarity and spatial organization
  * **Dynamic instability**: Rapid growth and shrinkage

===== ~~CLOSE~~ Septins (Emerging Group) =====
  * **Diameter**: ~10 nm (filament-like structures)
  * **Main proteins**: GTP-binding septins
  * **Polarity**: Yes (suggested)
  * **Functions**:
    * Cytokinesis (septin ring)
    * Membrane dynamics
    * Cell polarity
    * Potential scaffolding role
  * **Status**: Considered a "fourth cytoskeletal system" by some researchers

===== Summary Table =====

^ Component             ^ Diameter  ^ Protein(s)              ^ Polarity ^ Main Functions                                   ^
| Microfilaments        | ~7 nm     | Actin                   | Yes      | Shape, motility, endocytosis, cytokinesis        |
| Intermediate Filaments| ~10 nm    | Keratin, vimentin, etc. | No       | Mechanical support, nuclear structure            |
| Microtubules          | ~25 nm    | α/β-tubulin             | Yes      | Transport, division, cilia/flagella, polarity    |
| Septins (optional)    | ~10 nm    | Septins (GTP-binding)   | Suggested| Cytokinesis, polarity, scaffolding               |