Wednesday, June 13, 2012

Smooth Muscle

● What is smooth muscle?

Smooth muscle is muscle that is involuntary and that is not striated. There are two subgroups of smooth muscle: single unit, and multi unit. Single unit smooth muscle, which is also known as unitary smooth muscle, is innervated at the single cell level by the autonomic nervous system. The single cells are located within bundles or sheets of muscle tissue.

The action potential from the nervous system moves to accompanying cells through gap junctions in a way that leads to the contraction of the entire sheet or bundle. This whole sheet contraction is known as a syncytium, which is a cytoplasm mass with many nuclei that does not have separation into individual cells.

Smooth muscle tissues in the multi unit groupings also have nerve penetrations at the individual cell level. As a result, gradual responses can occur, including those responsible for fine motor control, similar to the way motor units control fine movements through skeletal muscles.

Smooth muscle is located in a variety of regions within the human body, including inside the blood vessel walls, where it is known as vascular smooth muscle. It is also found in the tunica media part of small and large arteries, veins, and arterioles.

Smooth muscle is also located in the urinary bladder, the lymphatic vessels, the uterus, where it is known as uterine smooth muscle, the respiratory and gastrointestinal tracts, the female and male reproductive tracts, the iris of the eye, and the ciliary muscle.

Smooth muscle cells are essentially structured and work the same way regardless of which organs they inhabit, but the stimuli required to trigger them vary considerably, which is why they can perform unique actions within the body at different times. The kidney glomeruli also host cells that resemble smooth muscle cells; these are known as mesangial cells.



(Image from: Actin myosin filaments)


● What is the molecular structure of smooth muscle tissue?

Much of what makes up smooth muscle cell cytoplasm is composed of actin and myosin molecules. Together, actin and myosin can contract. There are several tensile structures linked in a chain that allow the full smooth muscle tissue to contract with myosin and actin.


● An introduction to smooth muscle myosin

Myosin is predominantly composed of class ii when found in smooth muscle. Class ii myosin involves a pair of heavy chains that make up the head and tail areas. The heavy chains include N terminal head domains and C terminals are arranged in coiled coils that keep the two heavy chains linked. As a result, two heads are present in myosin ii.

There are also 4 light chains in myosin ii, with 2 chains in each head. These light chains keep the heavy chains together between the tail and the head. Hundreds of kinds of myosin structures can be made from different light and heavy chain combinations.


● An introduction to smooth muscle actin

The contractile machinery is made up of thin filaments that are primarily made from a and y actin. Alpha actin, or a actin in smooth muscle, is the isoform of smooth muscle that is most common. B actin is also quite prevalent, but it does not affect muscle contraction. B actin forms a polymer beneath the plasma membrane when a contracting stimulant is present, which means it might help in generating or sustaining mechanical tension.

Alpha actin also has unique isoforms at a genetic level, which means that there are specific isoforms in skeletal muscle, smooth muscle, and cardiac muscle with alpha actin. There is between 2 and 10 times as much myosin as actin in smooth muscle, while the ratio of myosin to actin is 6 to 1 in skeletal muscle and 4 to 1 in muscles within the heart.


● What is a smooth muscle actin antibody?

A smooth muscle actin antibody helps tag myoepithelial cells, myofibroblasts, and ordinary smooth muscle cells. The actin antibody can prove helpful for helping physicians identify a variety of muscular cancers and neoplasms, including pleomorphic adenomas, leiomyosarcomas, and leiomyomas.

The antibody is sensitive to the alpha actin form of smooth muscles. The antibody tends to specifically react with this actin when immunoblotting assays are performed. The antibody helps label the cells in smooth muscle in tissue sections that are embedded in paraffin, fixed in formalin, or frozen.


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