Where is smooth muscle found?
Smooth muscle is a type of tissue found in the walls of hollow organs, such as the intestines, uterus and stomach . You can also find smooth muscle in the walls of passageways, including arteries and veins of de cardiovascular system. This type of involuntary non-striated muscle is also found in the tracts of the urinary, respiratory and reproductive systems. In addition to that, you can find smooth muscle in the eyes, where it acts to change the size of the iris and the shape of the lens. The skin is also contains smooth muscle which allows hair to raise in response to cold temporatures or fear.
How thick is a smooth muscle cell?
The smooth muscle cell is 3-10 µm thick and 20-200 µm long. The cytoplasm is homogeneously eosinophilic and consists mainly of myofilaments. The nucleus is located in the center and takes a cigar-like shape during contraction. The cell membrane forms small pouch-like invaginations into the cytoplasm (caveolae) which are functionally equivalent to the T-tubules of the skeletal musculature. The smooth muscle cells are anchored to the surrounding connective tissue by a basal lamina.
What is the function of myofibroblasts in smooth muscle?
They produce connective tissue proteins such as collagen and elastin for which reason they are also referred to as fixed (or stationary) connective tissue cells.
What type of tissue does myofibroblasts produce?
Myofibroblasts produce connective tissue proteins such as collagen and elastin.
Which muscle group allows for cells to contract much stronger than those of striated musculature?
Fibers of smooth muscle group in branching bundles, which allows for cells to contract much stronger than those of striated musculature.
What is the cell membrane of skeletal muscle?
The cell membrane forms small pouch-like invaginations into the cytoplasm (caveolae) which are functionally equivalent to the T-tubules of the skeletal musculature. The smooth muscle cells are anchored to the surrounding connective tissue by a basal lamina. The smooth muscle fibers group in branching bundles.
Which muscle fibers are branching bundles?
The smooth muscle fibers group in branching bundles. As opposed to skeletal muscle fibers these bundles do not run strictly parallel and ordered but consist in a complex system. Thus the cells can contract much stronger than striated musculature.
Where is smooth muscle found?
Smooth muscle is found throughout the body where it serves a variety of functions. It is in the stomach and intestines where it helps with digestion and nutrient collection. It is found throughout the urinary system where it functions to help rid the body of toxins and works in electrolyte balance. It is found throughout arteries and veins where it plays a vital role in the regulation of blood pressure and tissue oxygenation. Without these vital functions, the body would not be able to maintain the most basic functions.
What is the function of smooth muscle?
Similar to the blood supply, the innervation of smooth muscle varies widely by location and function. Vascular smooth muscle is primarily innervated by the sympathetic nervous system. Alpha-1 and alpha-2 receptors function to cause vasoconstriction by contracting vascular smooth muscle cells leading to systemic hypertension. Beta-2 receptors also respond to sympathetic stimulation but produce a vasodilatory effect and which will lead to systemic hypotension. However, parasympathetic stimulation also plays an important role in the contraction of smooth muscle cells. Studies performed as early as 1925 demonstrated the effect of parasympathetic innervation on the gastrointestinal tract.[8] More recently researchers have been able to show how the sympathetic, parasympathetic, and enteric nervous systems all work uniformly to effect and contract smooth muscle.[9] Sympathetic stimulation of smooth muscle is received by contributions from spinal levels T1 to L2 of the spine. Each of these contributions finds its way into the sympathetic trunk which functions to route autonomic nervous supply to organs and tissue throughout the body. The parasympathetic nervous system functions in three parts, the cranial nerves, vagus nerve, and pelvic splanchnic nerves. Each nerve in the parasympathetic system regulates a specific portion of the body, the vagus, for instance, innervates the gastrointestinal tract from the esophagus to the proximal portion of the large intestines, while also sending out branches to the heart, larynx, trachea, bronchi, liver, and pancreas. The sympathetic and parasympathetic nervous systems are collectively referred to as the autonomic nervous system. The complex nature of the autonomic nervous system allows for tight unconscious control of digestions, respiratory rate, urination, heart rate, blood pressure, and many other critical body functions.
How does calcium release in smooth muscle tissue?
Ultimately innervation from the autonomic nervous system leads to a calcium release in smooth muscle tissue. Smooth muscle contraction is dependent on calcium influx. Calcium is increased within the smooth muscle cell through two different processes. First depolarization, hormones, or neurotransmitters cause calcium to enter the cell through L-type channels located in the caveolae of the membrane. Intracellular calcium then stimulates the release of calcium from the sarcoplasmic reticulum (SR) by way of ryanodine receptors and IP3, this process is referred to as calcium-induced calcium release.[10] Unlike skeletal muscle, smooth muscle calcium release from the sarcoplasmic reticulum is not physically coupled to the ryanodine receptor. Once calcium has entered the cell it is free to bind calmodulin, which transforms into activated calmodulin. Calmodulin then activates the enzyme myosin light chain kinase (MLCK), MLCK then phosphorylates a regulatory light chain on myosin. Once phosphorylation has occurred a conformational change takes place in the myosin head, this increases myosin ATPase activity which promotes interaction between the myosin head and actin. Cross-bridge cycling then occurs, and tension is generated. The tension generated is relative to the amount of calcium concentration within the cell. ATPase activity is much lower in smooth muscle than it is in skeletal muscle. This factor leads to the much slower cycling speed of smooth muscle. However, the longer period of contraction leads to a potentially greater force of contraction in smooth muscle. Smooth muscle contraction is enhanced even further through the use of connexins. Connexins allow for intercellular communication by allowing calcium and other molecules to flow to neighboring smooth muscle cells. This action allows for rapid communication between cells and a smooth contraction pattern.
How does smooth muscle differ from skeletal muscle?
Smooth muscle differs from skeletal muscle in function. Unlike skeletal muscle, smooth muscle is capable of maintaining tone for extended periods and often contracts involuntarily. At a cellular level, smooth muscle can be described as an involuntary, non-striated muscle. Smooth muscle consists of thick and thin filaments that are not arranged into sarcomeres giving it a non-striated pattern. On microscopic examination, it will appear homogenous. Smooth muscle cytoplasm contains a large amount of actin and myosin. Actin and myosin act as the main proteins involved in muscle contraction. Actin filaments attach to dense bodies that are spread throughout the cell. Dense bodies can be observed under an electron microscope and appear dark. Another important structure is the calcium-containing sarcoplasmic reticulum which aids in sustaining contraction. The shape of the smooth muscle is described as fusiform, which is described as being round in the center and tapering at each end. Smooth muscle can tense and relax but has greater elastic properties than striated muscle. This is important in organ systems like the urinary bladder where contractile tone must be preserved.
What is the function of actin and myosin?
Actin and myosin form continuous chains within the smooth muscle cell which are anchored at the dense bodies. The intermediate and thin filaments formed by the actin and myosin chains can then stretch to dense bodies located on adjacent smooth muscle cells forming a mesh-like network encircling a large number of smooth muscle cells. By implementing adherens junctions or connexins, the smooth muscle cells contract uniformly in what has been described as a spiral corkscrew fashion.
How does smooth muscle work?
A person does not need to think about their blood pressure for it to adapt to increasing oxygen demands from exercise. The nervous system instead uses hormones, neurotransmitters, and other receptors to control smooth muscle spontaneously.
How does smooth muscle affect blood flow?
It becomes more important to recognize how smooth muscles impact blood supply themselves. For example, within the cardiovascular system, smooth muscle helps to regulate blood flow by controlling the diameter of the vessel. As previously discussed vascular pathologies of smooth muscle can have devasting effects on the body and lead to significant pathology. Atherosclerosis once thought to be only a function of hemodynamics and vessel structure has more recently been shown to be linked as well to smooth muscle development.[4] Research has even shown that continuous vascular smooth muscle activation can lead to the formation of pulmonary hypertension.[6] Within the lungs, pathologic activation of smooth muscle can lead to the development of asthma. Asthma occurs when smooth muscle constriction leads to obstruction of the airway. Recent studies have shown that the smooth muscle layer may be increased in thickness before the onset of asthma even occurs, from which a genetic link may be derived. [7]
What are the types of smooth muscles in the human body?
Single-unit smooth muscle – a type of smooth muscle found in many organs, such as the stomach and intestines. It can be found both inside and outside these organ tissues.
Where is smooth muscle found?
Smooth muscle is a type of non-striated muscle that is found in the walls of hollow organs and blood vessels. Smooth muscle can be found throughout the body but is most common around the digestive tract, in the walls of blood vessels, arteries, and around other organs such as the eyes.
What disorders affect smooth muscles?
Certain disorders can also affect the functioning of smooth muscles. For instance, a genetic condition called Multisystemic smooth muscle dysfunction syndrome (MSMDS) results in an embryo to not develop enough smooth muscles for the digestive system. Some autoimmune disorders such as hepatitis, lupus or cirrhosis can also cause Anti-smooth muscle antibodies (ASMA).
What type of muscle is not striated?
As stated above, smooth muscle cells are not striated. This means they have no visible bands of contractile proteins like those found in skeletal muscles. These muscles are also involuntary, which means the contraction of these muscles is not dependent on conscious thought. They can contract in response to chemical or electrical signals, which they receive from autonomic nerves and hormones like epinephrine and vasopressin. Smooth muscle tissues are usually arranged as circular layers and tubes around the gut or as sheets between layers of connective tissue. Furthermore, this type of muscle has no more than one nucleus per cell.
What are the three types of muscular tissue?
The human body contains three main types of muscular tissue: skeletal, cardiac, and smooth. Smooth muscle is a type of non-striated muscle that is common in the walls of hollow organs and blood vessels. However, smooth muscle can be found throughout the body but is most common around the digestive tract, in the walls of blood vessels, arteries, and around other organs such as the eyes.
Which muscle is responsible for transporting blood throughout the body?
The vasculature system that transports blood throughout the body is controlled by smooth muscle. Smooth muscles contract to regulate blood pressure and other cardiovascular processes. They also aid in food digestion through peristalsis, which is the rhythmic wave-like contraction of muscles around the digestive tract.
What is a smooth muscle?
Smooth muscle, also called involuntary muscle, muscle that shows no cross stripes under microscopic magnification. It consists of narrow spindle-shaped cells with a single, centrally located nucleus.
Where is smooth muscle located?
Because vertebrate smooth muscle is located in the walls of many hollow organs, the normal functioning of the cardiovascular, respiratory,... This article was most recently revised and updated by Richard Pallardy, Research Editor.
What is the involuntary muscle?
See Article History. Alternative Title: involuntary muscle. Smooth muscle, also called involuntary muscle, muscle that shows no cross stripes ...
What is the stomach composed of?
It constitutes much of the musculature of internal organs and the digestive system. Smooth muscle cells. The stomach is composed of smooth muscle cells. Because vertebrate smooth muscle is located in the walls of many hollow organs, the normal functioning of the cardiovascular, respiratory,...
Where is smooth muscle located?
Whereas cardiac muscle is only located in the heart, and skeletal muscles mostly attach to bones, smooth muscle tissue is found throughout the body. To remember the main locations, I created a simple mnemonic to help you.
How does smooth muscle work?
For example, in most of the digestive tract, smooth muscle cells are formed in two layers with different orientations, which work together to propel food down the digestive tract, a process known as peristalsis.
Why does smooth muscle not have striations?
Because smooth muscle lacks myofibrils and sarcomeres, it does not contain the striations (or striped pattern) that characterizes both skeletal and cardiac muscle tissue. And that’s an important point to remember for exams: smooth muscle is the only muscle tissue type that does not contain striations, and that’s why it’s called “smooth.”
What is the structure of skeletal muscle?
Skeletal Muscle Structure. Each skeletal muscle is considered an organ, and it’s made up of connective tissue layers, muscle fibers, blood vessels, and nerves. Skeletal muscles attach to the bones through tendons or through a direct attachment. As you look at this muscle diagram, you’ll notice an outer layer of connective tissue called epimysium.
What type of muscle tissue is most commonly attached to bones?
Skeletal Muscle Tissue. Skeletal muscles most commonly attach to bones, and they help you move your body. Unlike the other two types of muscle tissue, skeletal muscles contract on a voluntary basis via the somatic nervous system, allowing you to move your body at will. Skeletal muscles also serve important functions, ...
How many nuclei are in skeletal muscle?
Another difference is that skeletal muscle contains multiple nuclei that are scattered around the peripheral portion of the muscle cells, whereas cardiac muscle contains only 1-2 nuclei, which are located near the center of the cell.
Which muscle tissue has the same filaments as the muscle fiber?
However, smooth muscle tissue does consist of the same thin (actin) filaments and thick (myosin) filaments found in both skeletal and cardiac muscle tissue, which work to contract the muscle fiber via a sliding filament mechanism.