A myoneme (or spasmoneme) is a contractile structure found in some
eukaryotic
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
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 with the 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 ...
. Although the shortening can be up to 100 lengths per second, faster than any muscle, the
relaxation time
In the physical sciences, relaxation usually means the return of a perturbed system into equilibrium.
Each relaxation process can be categorized by a relaxation time τ. The simplest theoretical description of relaxation as function of time ' ...
is several seconds (compared to approximately one tenth of a second for muscle). The myonemes of
Acantharea
The Acantharea (Acantharia) are a group of radiolarian protozoa, distinguished mainly by their strontium sulfate skeletons. Acantharians are heterotrophic marine microplankton that range in size from about 200 microns in diameter up to several ...
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]
References
Cell biology