Smooth muscle

Layers of Esophageal Wall:
1. Mucosa
2. The mucous membranes (or mucosae; singular mucosa) are linings of mostly endodermal origin covered in Epithelium, which are involved in Submucosa
3. In the Gastrointestinal tract, the submucosa is the layer of Loose connective tissue that supports the Mucosa, as well as joins the mucosa to the bulk Muscularis
4. Adventitia
5. Adventitia is the outermost Connective tissue covering of any organ, vessel, or other structure Striated muscle
6. Striated muscle is a form of fibres that are combined into parallel fibres Striated and smooth
7. Smooth muscle
8. Lamina muscularis mucosae
9. The lamina muscularis mucosae (or "muscularis mucosa" is the thin layer of Smooth muscle found in most parts of the Gastrointestinal tract, located Esophageal glands

Smooth muscle is a type of non-striated muscle, found within the tunica media layer of arteries and veins, the bladder, uterus, male and female reproductive tracts, gastrointestinal tract, respiratory tract, the ciliary muscle, and iris of the eye. The esophageal glands are small compound Racemose Exocrine glands of the Mucous type Striated muscle is a form of fibres that are combined into parallel fibres The tunica media (or just media) ( middle coat) is the middle layer of an Artery or Vein. Arteries are Blood vessels that carry blood away from the Heart. In the Circulatory system, a vein is a Blood vessel that carries Blood back toward the Heart (as opposed to Artery, a blood vessel In Anatomy, the urinary bladder is a hollow muscular, and distensible (or elastic organ that sits on the Pelvic floor in Mammals It is the The uterus (from the Latin word for womb) is the major Female reproductive organ of most Mammals including Humans One end the In humans the respiratory tract is the part of the Anatomy that has to do with the process of respiration. The glomeruli of the kidneys contain a smooth muscle-like cell called the mesangial cell. A glomerulus is a Capillary tuft surrounded by Bowman's capsule in Nephrons of the vertebrate Kidney. Smooth muscle is fundamentally different from skeletal muscle and cardiac muscle in terms of structure, function, excitation-contraction coupling, and mechanism of contraction. Skeletal muscle is a type of Striated muscle, which usually attaches to tendons The cardiac muscle is a type of involuntary striated Muscle found in the walls of the Heart.

Structure

Smooth muscle fibers are spindle-shaped, and, like all muscle, can contract and relax. A muscles contraction (also known as a muscle twitch or simply twitch) occurs when a Muscle fibre generates tension through the action of Actin In the relaxed state, each cell is spindle-shaped, 20-500 micrometers long, and 5 micrometers wide. ^[1] There are two types of smooth muscle arrangements in the body: multi-unit and single-unit. The single-unit type, also called unitary smooth muscle, is far more common. Whereas the former presents itself as distinct muscle fibers that are usually activated by their own nerve fibers, the latter operate as a single unit and are arranged in sheets or bundles. An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell Unitary smooth muscle is also commonly referred to as visceral smooth muscle because it is found in the walls of the viscera, or internal organs, of the body, including the intestines, ducts such as the bile ducts, ureters and oviducts, and most blood vessels. In Anatomy, a viscus (ˈvɪskəs ( Plural: viscera /ˈvɪsərə/ is an internal organ of an animal (including humans in particular an internal In Anatomy, the intestine is the segment of the alimentary canal extending from the Stomach to the Anus and in humans and other mammals consists A bile duct is any of a number of long tube-like structures that carry Bile. In human Anatomy, the ureters are muscular ducts that propel Urine from the Kidneys to the Urinary bladder. Oviduct is also another name for Fallopian tube In Oviparous Animals (those that lay eggs, the passage from the ovaries The blood vessels are part of the Circulatory system and function to transport Blood throughout the body ^[2] Unitary smooth muscle can be further divided into phasic and tonic.

The cells that compose smooth muscle have, in general, single nuclei. In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed The cells are arranged in sheets or bundles and connected by gap junctions. A gap junction or nexus is a specialized Intercellular connection between certain animal cell -types In order to contract, the cells contain actin filaments and a contractous protein called myosin. Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of Myosins are a large family of Motor proteins found in Eukaryotic tissues. Whereas the filaments are essentially the same in smooth muscle as they are in skeletal and cardiac muscle, the way they are arranged is different. Some regulatory proteins also differ, and there are specific smooth muscle isoforms of actin and myosin. The smooth muscle cell contains less protein than a typical striated muscle cell and much less myosin. The actin content is similar, so the ratio of actin to myosin is ~6:1 in striated muscle and ~15:1 in smooth muscle. Smooth muscle does not contain the protein troponin, (calmodulin takes on the regulatory role in smooth muscle) and caldesmon and calponin are significant proteins expressed within smooth muscle. Troponin is a complex of three regulatory proteins that is integral to Muscle contraction in skeletal and Cardiac muscle, but not Smooth muscle Calmodulin ( CaM) (an abbreviation for CAL cium MODUL ated prote' IN') is a calcium-binding protein expressed in all Eukaryotic cells Caldesmon 1, also known as CALD1, is a human Gene. Caldesmon is a Calmodulin binding protein. As non-striated muscle, the actin and myosin are not arranged into distinct sarcomeres that form orderly bands throughout the muscle cell. "A-band" redirects here For other uses of the term see A band. However, there is an organized cytoskeleton consisting of the intermediate filament proteins vimentin and desmin, along with actin filaments. Actin filaments attach to the sarcolemma by focal adhesions or attachment plaques and attach to other actin filaments via dense bodies (acting much like Z-lines in striated muscle). Evidence indicates that smooth muscle myosin is not bipolar with a central bare zone as in striated muscle, but is either side-polar or row-polar, and has no bare zone. Some smooth muscle preparations can be visualized contracting in a spiral corkscrew fashion, and contractile proteins can organize into zones of actin and myosin along the axis of the cell.

The sarcolemma possess microdomains specialized to cell-signaling events and ion channels called caveolae. These invaginations in the sarcoplasma contain a host of receptors (prostacyclin, endothelin, serotonin, muscarinic receptors, adrenergic receptors), second messenger generators (adenylate cyclase, Phospholipase C), G proteins (RhoA, G alpha), kinases (rho kinase-ROCK, Protein kinase C, Protein Kinase A), ion channels (L type Calcium channels, ATP sensitive Potassium channels, Calcium sensitive Potassium channels) in close proximity. In Biochemistry, a receptor is a Protein molecule embedded in either the Plasma membrane or Cytoplasm of a cell to which a mobile signaling Prostacyclin (or PGI2) is a member of the family of Lipid Molecules known as Eicosanoids. Endothelins are proteins that constrict blood vessels and raise blood pressure Serotonin (ˌsɛrəˈtoʊnən ( 5-hydroxytryptamine, or 5-HT) is a Monoamine Neurotransmitter synthesized in serotonergic Neurons In Cell physiology, a secondary messenger system (also known as a second messenger system) is a method of cellular signaling whereby a diffusable signaling molecule Ion channels are pore-forming Proteins that help establish and control the small Voltage Gradient across the Plasma membrane of all living The caveolae are often in close proximity to sarcoplasmic reticulum or mitochondria, and have been proposed to organize signaling molecules in the membrane.

Function

To maintain organ dimensions against forces, cells are fastened to one another adherens junctions. Adherens junctions (or zonula adherens) are protein complexes that occur at cell-cell junctions in epithelial tissues usually more basal than Tight junctions. As a consequence, cells are mechanically coupled to one another such that contraction of one cell invokes some degree of contraction in an adjoining cell. Gap junctions couple adjacent cells chemically and electrically, facilitating the spread of chemicals (e. g. , calcium) or action potentials between smooth muscle cells. Smooth muscle may contract spontaneously (via ionic channel dynamic or Cajal pacemaker cells) or be induced by a number of physiochemical agents (e. g. , hormones, drugs, neurotransmitters - particularly from the autonomic nervous system), and also mechanical stimulation (such as stretch). &trade The autonomic nervous system ( ANS) (or visceral nervous system) is the part of the Peripheral nervous system that acts as a Control

Smooth muscles have been divided into "multi-unit" and "visceral" types or into "phasic" and "tonic" types based on the characteristics of the contractile patterns. It may contract phasically with rapid contraction and relaxation, or tonically with slow and sustained contraction. The reproductive, digestive, respiratory, and urinary tracts, skin, eye, and vasculature all contain this tonic muscle type. For example, contractile function of vascular smooth muscle is critical to regulating the lumenal diameter of the small arteries-arterioles called resistance vessels. The resistance arteries contribute significantly to setting the level of blood pressure. Smooth muscle contracts slowly and may maintain the contraction (tonically) for prolonged periods in blood vessels, bronchioles, and some sphincters. In the digestive tract, smooth muscle contracts in a rhythmic peristaltic fashion, rhythmically forcing foodstuffs through the digestive tract as the result of phasic contraction. In the Esophagus After food is chewed into a bolus it is swallowed to move it into the esophagus

Smooth muscle in various regions of the vascular tree, the airway and lungs, kidneys, etc. is different in their expression of ionic channels, hormone receptors, cell-signaling pathways, and other proteins that determine function. Smooth muscle-containing tissue often must be stretched, so elasticity is an important attribute of smooth muscle. Smooth muscle cells may secrete a complex extracellular matrix containing collagen (predominantly types I and III), elastin, glycoproteins, and proteoglycans. Collagen is the main Protein of Connective tissue in Animals and the most abundant protein in Mammals making up about 50% of the whole-body protein Elastin is a Protein in Connective tissue that is elastic and allows many tissues in the body to resume their shape after stretching or contracting Not to be confused with Peptidoglycan. Glycoproteins are proteins that contain Oligosaccharide chains ( Glycans) covalently attached Proteoglycans represent a special class of Glycoproteins that are heavily glycosylated. These fibers with their extracellular matrices contribute to the viscoelasticity of these tissues. Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Smooth muscle also has specific elastin and collagen receptors to interact with these proteins.

Contraction and relaxation basics

Smooth muscle contraction is caused by the sliding of myosin and actin filaments (a sliding filament mechanism) over each other. Myosins are a large family of Motor proteins found in Eukaryotic tissues. Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of The energy for this to happen is provided by the hydrolysis of ATP. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy Myosin functions as an ATPase utilizing ATP to produce a molecular conformational change of part of the myosin and produces movement. Movement of the filaments over each other happens when the globular heads protruding from myosin filaments attach and interact with actin filaments to form crossbridges. The myosin heads tilt and drag along the actin filament a small distance (10-12 nm). The heads then release the actin filament and adopt their original conformation. They can then re-bind to another part of the actin molecule and drag it along further. This process is called crossbridge cycling and is the same for all muscles (see muscle contraction). A muscles contraction (also known as a muscle twitch or simply twitch) occurs when a Muscle fibre generates tension through the action of Actin Unlike cardiac and skeletal muscle, smooth muscle does not contain the calcium-binding protein troponin. Contraction is initiated by a calcium-regulated phosphorylation of myosin, rather than a calcium-activated troponin system.

Crossbridge cycling cannot occur until the myosin heads have been activated to allow crossbridges to form. The myosin heads are made up of heavy chains and light protein chains. When the light chains are phosphorylated, they become active and will allow contraction to occur. The enzyme that phosphorylates the light chains is called myosin light-chain kinase (MLCK). Myosin-light-chain kinase (MLCK is a serine/threonine-specific protein kinase that Phosphorylates the regulatory light chain of Myosin II. In order to control contraction, MLCK will work only when the muscle is stimulated to contract. Stimulation will increase the intracellular concentration of calcium ions. These bind to a molecule called calmodulin, and form a calcium-calmodulin complex. Calmodulin ( CaM) (an abbreviation for CAL cium MODUL ated prote' IN') is a calcium-binding protein expressed in all Eukaryotic cells It is this complex that will bind to MLCK to activate it, allowing the chain of reactions for contraction to occur. The phosphorylation of the light chains by MLCK is countered by a myosin light-chain phosphatase, which dephosphorylates the myosin light chains and inhibits the contraction. Other signaling pathways have also been implicated in the regulation actin and myosin dynamics. In general, the relaxation of smooth muscle is by cell-signaling pathways that increase the myosin phosphatase activity, decrease the intracellular calcium levels, hyperpolarize the smooth muscle, and/or regulate actin and myosin dynamics.

Invertebrate smooth muscle

In invertebrate smooth muscle, contraction is initiated with the binding of calcium directly to myosin and then rapidly cycling cross-bridges, generating force. Similar to the mechanism of vertebrate smooth muscle, there is a low calcium and low energy utilization catch phase. This sustained phase or catch phase has been attributed to a catch protein that has similarities to myosin light-chain kinase and the elastic protein-titin called twitchin. Mollusk-like clams use this catch phase of smooth muscle to keep their shell closed for prolonged periods with little energy usage.

Control

Smooth muscle cells can be stimulated to contract or relax in many different ways. They may be directly stimulated by the autonomic nervous system ("involuntarily" control), but can also react on stimuli from neighbouring cells and on hormones (vasodilators or vasoconstrictor) within the medium that it carries. &trade The autonomic nervous system ( ANS) (or visceral nervous system) is the part of the Peripheral nervous system that acts as a Control A volunteer is someone who works for a community or for the benefit of environment primarily because they choose to do so Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels particularly the large Arteries, Arterioles

Growth and rearrangement

The mechanism in which external factors stimulate growth and rearrangement is not yet fully understood. A number of growth factors and neurohumoral agents influence smooth muscle growth and differentiation. The Notch receptor and cell-signaling pathway have been demonstrated to be essential to vasculogenesis and the formation of arteries and veins.

The embryological origin of smooth muscle is usually of mesodermal origin. However, the smooth muscle within the Aorta and Pulmonary arteries (the Great Arteries of the heart) is derived from ectomesenchyme of neural crest origin, although coronary artery smooth muscle is of mesodermal origin.

Related diseases

"Smooth muscle condition" is a condition in which the body of a developing embryo does not create enough smooth muscle for the gastrointestinal system. This condition is fatal.

Anti-smooth muscle antibodies (ASMA) can be a symptom of an auto-immune disorder, such as hepatitis, cirrhosis, or lupus. Autoimmunity is the failure of an organism to recognize its own constituent parts as self, which results in an immune response against its own cells and tissues Hepatitis (plural hepatitides) implies injury to the Liver characterized by the presence of Inflammatory cells in the tissue of Cirrhosis is a consequence of chronic Liver Disease characterized by replacement of liver tissue by fibrous Scar tissue as well as regenerative Systemic lupus erythematosus ( SLE or lupus,) is a chronic autoimmune disease that can be fatal though with recent medical advances fatalities are becoming

Vascular smooth muscle tumors are very rare. They can be malignant or benign, and morbidity can be significant with either type. Intravascular leiomyomatosis is a benign neoplasm that extends through the veins; angioleiomyoma is a benign neoplasm of the extremities; vascular leiomyosarcomas is a malign neoplasm that can be found in the inferior vena cava, pulmonary arteries and veins, and other peripheral vessels.

See Atherosclerosis. Atherosclerosis is a Disease affecting arterial Blood vessels It is a chronic inflammatory response in the walls of arteries in large part due to the accumulation

References

See also

• Skeletal muscle
• Cardiac muscle
• Vascular smooth muscle

External links

• BBC - baby born with smooth muscle condition has 8 organs transplanted
• Smooth muscle antibody
• Stomach smooth muscle identified using antibody
• UIUC Histology Subject 265
• Histology at KUMC muscular-muscle08 "Smooth Muscle"
• Histology at BU 21701ooa
• Physiology at MCG 2/2ch8/2ch8line