Quick Facts
Cilia are minute vibratile, hairlike processes that project from the free surface of a cell and are composed of nine pairs of microtubules arrayed around a central pair, anchored to the cellular cortex by the basal bodies. Dynein-powered sliding of the outer microtubules relative to one another causes the cilia to move in rhythmic beats (ciliary beats) that move the cell around in its environment or move fluid or mucous films over the cell surface (Dorland, 2011).
Related parts of the anatomy
Structure and/or Key Features
Cilia are hairlike projections of the apical surface of the plasmalemma of many cells. Each cilium contains a unique (9+2) arrangement of microtubules called an axoneme extending from a basal body and a microtubule-organizing center all located in the apical region of the ciliated cell.
There are three categories of cilia:
—primary (non-motile) cilia;
—motile cilia (and flagella);
—nodal cilia which are found only in the embryo.
Motile cilia are about 0.25 μm in diameter and 5–10 μm long and are present in various locations including the apical surface of ependymal cells. In ciliated epithelium, there may be several hundred protecting from the apical cell surface. Their internal structure permits their wave-like motion. Each cilium is firmly anchored to the apical region of the cell cytoplasm by a microtubule organizing center or centriole (Mescher, 2013).
Anatomical Relations
The majority of cilia are predominantly found in epithelial cells. Cilia are abundant on the apical surfaces of cuboidal or columnar cells lining the upper respiratory tract and uterine tubes (Mescher, 2013).
Function
Motile cilia primarily assist in fluid movement along the surfaces of epithelium, e.g., cerebrospinal fluid along the surfaces of ependymal cells in the ventricles of the brain. As a flagellum, it provides movement of the spermatozoa (Ross and Pawlina, 2006).
Primary cilia can detect physical and biochemical signals (Standring, 2016).
Primary cilia are particularly important for normal tissue morphogenesis (Ross and Pawlina, 2006).
Nodal cilia are important during early development of the embryo (Ross and Pawlina, 2006).
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Mescher, A. (2013) Junqueira's Basic Histology: Text and Atlas. 13th edn.: McGraw-Hill Education.
Ross, M. H. and Pawlina, W. (2006) Histology: A text and atlas. Lippincott Williams & Wilkins.
Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41 edn.: Elsevier Limited.
