One of the most likely explanations for why intermediate filaments have no known motor proteins is because they are nonpolar. What this means is that there are no distinct ends to the filament. Motor proteins have ways of detecting which direction they are moving along actin or microtubules because they have distinct ends (polarization). Size should not affect the ability of a motor protein to function, especially because actin is smaller than intermediate filaments and microtubules are larger (hence the name "intermediate").

Eukaryotic flagella are composed of nine pairs of microtubules. In contrast, prokaryotic flagella are composed of the protein flagellin.

G-actin subunits that polymerize form microfilaments, also known as actin filaments. The other cytoskeletal components listed are formed from different proteins, but only microfilaments are actin-based structures. 

Tubulin is a key protein found in microtubules. Microtubules are large cytoskeletal elements that have several functions inside a cell. One of the biggest use of microtubules arises during mitosis. Recall that chromosomes are pulled apart to opposite ends during the anaphase of mitosis. The rope-like substances that pull these chromosomes to opposite ends of cell are microtubule segments. In addition, microtubules are also involved in axonal transport in neurons. Some nerves (such as sciatic nerve) can have extremely long axons. To maintain the integrity of these distal ends of the axons, nutrients and other important molecules from the cell body of a neuron are carried, along microtubule segments, to axon terminals; therefore, microtubules are also essential for axonal transport.

Recall that tubulin is an essential component of microtubules. Administering Vincristine to cancer patients will halt the synthesis of microtubules in cancer cells, thereby inhibiting several essential cellular processes (such as mitosis). This will prevent proliferation of the cancer cells. There are three cytoskeletal elements; microtubules, microfilaments, and intermediate filaments. Of the three, microtubules are the biggest, followed by intermediate filaments. Recall that microtubules are also involved in axonal transport in neurons; therefore, halting microtubule synthesis in neurons could result in nerve problems and neuropathies.

Actin-myosin interactions involved in muscle contraction do not depend on the microtubules; therefore, Vincristine will not affect muscle contraction. Note that actin filaments make up microfilaments; therefore, any damage to actin (and microfilaments) will affect muscle contraction.

Microfilaments are the smallest of the three cytoskeletal elements and are made up of actin filaments (myosin is not found in microfilaments). The 9+2 arrangement is found in microtubules, the biggest cytoskeletal elements. The third cytoskeletal element is called the intermediate filament and is made up of related proteins unique to each intermediate filament.