Motility

For the Steve Kuhn album, see Motility (album).

"Motile" redirects here. For the independent British record label, see Motile (record label).

Cell division. All cells can be considered motile for having the ability to divide into two new daughter cells.

Our muscles give us the ability to move voluntarily (e.g. to throw a ball) and involuntarily (e.g. muscle spasms and reflexes). At the level of the muscular system, motility is a synonym for locomotion.

Eukaryotic cytoskeletons induce cells to move through liquid and over surfaces, divide into new cells, and the cytoskeleton guides the transport of organelles within the cell. This video captures stained cytoskeletons from the cross section of a leaf of Arabidopsis thaliana.

In biology, motility is the ability to move spontaneously and actively, consuming energy in the process. Motility is genetically determined (see genetic determinism) but may be affected by environmental factors. For instance, muscles give animals motility but the consumption of hydrogen cyanide (the environmental factor in this case) would adversely affect muscle physiology causing them to stiffen leading to rigor mortis. Most animals are motile but the term applies to unicellular and simple multicellular organisms, as well as to some mechanisms of fluid flow in multicellular organs, in addition to animal locomotion. Motile marine animals are commonly called free-swimming.

Motility may also refer to an organism's ability to move food through its digestive tract, i.e., peristaltics (gut motility, intestinal motility, etc.).

Cellular-level motility

At the cellular level, different modes of motility exist:

• flagellar motility, a swimming-like motion (observed for example in spermatozoa, propelled by the regular beat of their flagellum, or E. coli, which swims by rotating a helical prokaryotic flagellum)
• amoeboid movement, a crawling-like movement, which also makes swimming possible
• gliding motility
• Swarming motility

Many cells are not motile, for example Klebsiella pneumoniae and Shigella, or under specific circumstances such as Yersinia pestis at 37 °C.

Movements

See also: Taxis

The events that are perceived as movements can be directed:

• along a chemical gradient (see chemotaxis)
• along a temperature gradient (see thermotaxis)
• along a light gradient (see phototaxis)
• along a magnetic field line (see magnetotaxis)
• along an electric field (see galvanotaxis)
• along the direction of the gravitational force (see gravitaxis)
• along a rigidity gradient (see durotaxis)
• along a gradient of cell adhesion sites (see haptotaxis)
• along other cells or biopolymers

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  Most sperm have a single flagellum to help them swim. The cervical, uterine, and fallopian linings of the female reproductive system play a more important role in transporting sperm to ova.

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  The record speeds Cheetahs hold are owed in large to their muscle motility.

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  The shoots of plants move by growing towards light. This is known as positive phototropism. The roots grow away from light. This is known as positive geotropism.

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  Natural killer cells, monocytes, and macrophages of the immune system engulf Bacteria by extending their pseudopodia. Note that this cartoon is not an accurate representation of phagocytosis.

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  Motility becomes very complicated at the sub-cellular level. Shown here is a simplified video animation of translation - a highly motile molecular process.

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  Usain Bolt's success relies on motility.

See also

• Cell migration