A myoneme (or spasmoneme) is a contractile structure found in some
eukaryotic
The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
single-celled organisms, particularly ''
Vorticella
''Vorticella'' is a genus of bell-shaped ciliates that have stalks to attach themselves to substrates. The stalks have contractile myonemes, allowing them to pull the cell body against substrates. The formation of the stalk happens after the fr ...
''.
It consists of a series of
protein filament
In biology, a protein filament is a long chain of protein monomers, such as those found in hair, muscle, or in flagella. Protein filaments form together to make the cytoskeleton of the cell. They are often bundled together to provide support, st ...
s that shorten rapidly upon exposure to
calcium
Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
. Although the shortening can be up to 100 lengths per second, faster than any muscle, the
relaxation time Relaxation stands quite generally for a release of tension, a return to equilibrium.
In the sciences, the term is used in the following ways:
* Relaxation (physics), and more in particular:
** Relaxation (NMR), processes by which nuclear magneti ...
is several seconds (compared to approximately one tenth of a second for muscle). The myonemes of
Acantharea
The Acantharia are a group of radiolarian protozoa, distinguished mainly by their strontium sulfate skeletons. Acantharians are heterotrophic marine Plankton, microplankton that range in size from about 200 microns in diameter up to several milli ...
also display slow contraction and undulation movements.
[{{cite journal, last=Febvre, first=Jean, title=The Myomene of the Acantharia (Protozoa): a new model of cellular motility, journal=BioSystems, year=1981, volume=14, issue=3–4, pages=327–336, doi=10.1016/0303-2647(81)90039-3, pmid=7199949 ]
References
Cell biology