Microfilaments are thin, threadlike cytoplasmic structures. Three classes of microfilaments exist: thin microfilaments, which are equivalent to the thin actin filaments in muscle; intermediate filaments, which are a heterogeneous group of filaments with diameter sizes between the thick and thin filaments; and thick myosin filaments, which are present in muscle cells but may also exist temporarily in other cells.
Muscle contraction depends on the interaction between the thin actin filaments and thick myosin filaments. Microfilaments are present in the superficial zone of the cytoplasm in most cells. Contractile activities involving the microfilaments and associated thick myosin filaments contribute to movement of the cytoplasm and cell membrane during endocytosis and exocytosis. Microfilaments
are also present in the microvilli of the intestine. The intermediate filaments assist in supporting and maintaining the asymmetric shape of cells. Examples of intermediate filaments are the keratin filaments that are found anchored to the cell membrane of epidermal keratinocytes of the skin and the glial filaments that are found in astrocytes and other glial cells of the nervous system. The neurofibril-lary tangle found in the brain in Alzheimer's disease contains microtubule-associated proteins and neurofilaments, evidence of a disrupted neuronal cytoskeleton.
No comments:
Post a Comment