CONTRACTILE CELLS
In addition to above mentioned three types of muscular tissue, there are contractile cells.
These are as follows.
1. Myoepithelial Cells (= Myoepitheliocytes). These cells are present in salivary glands, mammary glands and sweat glands. They form a sort of epithelium called myoepithelium. Myoepithelial cells contract to expel saliva, milk and sweat from the respective glands. Myopithelial cells are innervated by autonomic nerves. They resemble smooth muscle cells and are involuntary. These cells arise from the ectoderm instead of mesoderm.
2. Myofibroblasts. These cells resemble fibroblasts but contain actin and myosin arranged as in smooth muscle and are contractile. In fact myofibroblasts are specialised contractile fibroblasts. The contraction of wounds is caused by the shortening of myofibroblasts.
3. Pericytes. These cells are found around capillaries and venules. They contain actin and myosin. Pericytes can give rise to myofibroblasts and to mesenchymal tissue which can differentiate into fibroblasts and can form new blood vessels.