What organelles do muscle cells contain?
To meet this energy demand, muscle cells contain mitochondria. These organelles, commonly referred to as the cell's “power plants,” convert nutrients into the molecule ATP, which stores energy.
What do smooth muscle cells contain?
Smooth muscle contains thick and thin filaments that do not arrange into sarcomeres, resulting in a non-striated pattern. On microscopic examination, it appears homogenous. Smooth muscle cytoplasm contains large amounts of actin and myosin. Actin and myosin act as the main proteins involved in muscle contraction.
What cells are in smooth muscle tissue?
Smooth muscle in the gastrointestinal tract is activated by a composite of three types of cells – smooth muscle cells (SMCs), interstitial cells of Cajal (ICCs), and platelet-derived growth factor receptor alpha (PDGFRα) that are electrically coupled and work together as an SIP functional syncytium.
Do smooth muscle cells have mitochondria?
Although far less well studied, the mitochondria within smooth muscle are thought to play a role in maintaining vascular tone, facilitating cellular transport, and producing energy for vascular cell secretion (42, 46). These mitochondria typically comprise 3∼5% of the smooth muscle cell volume (3).
What is the structure and function of smooth muscle cell?
Smooth muscle is a type of muscle tissue which is used by various systems to apply pressure to vessels and organs. Smooth muscle is composed of sheets or strands of smooth muscle cells. These cells have fibers of actin and myosin which run through the cell and are supported by a framework of other proteins.
What is the structure and function of smooth muscle?
Summary. Smooth muscle is found in the wall of hollow organs, passageways, tracts, eye and skin. Fibers of smooth muscle group in branching bundles, which allows for cells to contract much stronger than those of striated musculature.
What cells are in muscles?
Muscle cells, commonly known as myocytes, are the cells that make up muscle tissue. There are 3 types of muscle cells in the human body; cardiac, skeletal, and smooth. Cardiac and skeletal myocytes are sometimes referred to as muscle fibers due to their long and fibrous shape.
What features are not present in smooth muscle quizlet?
Smooth muscle cells lack myofibrils and sarcomeres. Smooth muscle cells possess striations. Smooth muscle cells contain many nuclei. Smooth muscle cells contain a network of T tubules.
What are muscles made up of?
An individual muscle fibre is made up of blocks of proteins called myofibrils, which contain a specialised protein (myoglobin) and molecules to provide the oxygen and energy required for muscle contraction. Each myofibril contains filaments that fold together when given the signal to contract.
Which of the following organelles are found within a muscle fiber?
The sarcoplasmic reticulum of a skeletal muscle fiber stores calcium ions, which are released to initiate muscle contraction. Now, we know the structure within skeletal muscles that stores and releases calcium ions needed to initiate muscle contractions. This organelle is called the sarcoplasmic reticulum.
Do muscle cells have ribosomes?
In fact, the concentration of ribosomes in skeletal muscle, based on total RNA per milligram of tissue, was found to be the greatest at early stages of postnatal development; however, although the concentration of ribosomes progressively decreases during skeletal muscle growth and maturation, the total translation ...
Does smooth muscle have multiple mitochondria?
In contrast with other tissues, such as liver and heart, where the mitochondria are particularly abundant, the bulk of smooth muscle tissue consists of myofibrils and connective tissue with relatively few mitochondria.
What are smooth muscle cells?
Sanders, in Clinical and Basic Neurogastroenterology and Motility, 2020. Smooth muscle cells (SMCs) are the power house that generates the forces responsible for gastrointestinal motility.
What color is smooth muscle?
Smooth muscle cells may take on an epithelioid quality, as shown here, with very well-defined cell borders to the polygonal cells. The trichome stain can be used to highlight smooth muscle cells (red) and background collagen (blue) in cases of spindled cell tumors.
What is a quiescent SMC?
Quiescent SMC within the normal media of arteries are in close contact with an external lamina that contains basement membrane components, including type IV collagen, laminin, and perlecan. During intimal hyperplasia in response to arterial injury, medial SMCs are induced to migrate and proliferate in response to the release of growth factors both from injured cells and/or from platelets that bind to the lumenal surface of the vessel at sites of endothelial damage or denudation. The activation of medial SMCs is accompanied by changes in cellular structure, which has been termed phenotypic modulation, in which cellular contractile function and structure is decreased, and synthetic machinery in the cell is increased ( 80, 81 ). Such proliferative cells have a distinctive profile of ECM protein synthesis, including the synthesis of hyaluronan and versican, fibronectin and interstitial collagens, while decreasing the synthesis of basement membrane components, such as perlecan and laminins ( 82–84 ). It has been proposed that after arterial injury SMC transiently express a growth autonomic phenotype that has been associated with rapidly proliferating embryonic vessel wall SMCs ( 85 ). This phenotype is associated with the constitutive activation of distinctive signaling pathways, including those involving Akt, mTOR, and p70S6K ( 69 ), that are downstream from potential inhibitory signals engendered by cellular interaction with perlecan ( 68, 74 ).
Does IL-6 affect smooth muscle?
The importance of this action for human disease is unknown. Cytokines elaborated by smooth muscle cells during inflammation, particularly IL-6, can decrease the contractility of smooth muscle and can alter neurotransmission ( 225 ).
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.
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.
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 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.
Where can I find smooth muscle?
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.
Where are the actin filaments?
The actin filaments are stretched between dense bodies in the cytoplasm and attachment plaques at the cell membrane. The myosin filaments lie between the actin filaments. Furthermore intermediate filaments such as desmin and vimentin support the cell structure.
How do smooth muscle cells work?
Smooth muscle cells can undergo hyperplasia, mitotically dividing to produce new cells. The smooth cells are nonstriated, but their sarcoplasm is filled with actin and myosin, along with dense bodies in the sarcolemma to anchor the thin filaments and a network of intermediate filaments involved in pulling the sarcolemma toward the fiber’s middle, shortening it in the process. Ca ++ ions trigger contraction when they are released from SR and enter through opened voltage-gated calcium channels. Smooth muscle contraction is initiated when the Ca ++ binds to intracellular calmodulin, which then activates an enzyme called myosin kinase that phosphorylates myosin heads so they can form the cross-bridges with actin and then pull on the thin filaments. Smooth muscle can be stimulated by pacesetter cells , by the autonomic nervous system, by hormones, spontaneously, or by stretching. The fibers in some smooth muscle have latch-bridges, cross-bridges that cycle slowly without the need for ATP; these muscles can maintain low-level contractions for long periods. Single-unit smooth muscle tissue contains gap junctions to synchronize membrane depolarization and contractions so that the muscle contracts as a single unit. Single-unit smooth muscle in the walls of the viscera, called visceral muscle, has a stress-relaxation response that permits muscle to stretch, contract, and relax as the organ expands. Multiunit smooth muscle cells do not possess gap junctions, and contraction does not spread from one cell to the next.
How is smooth muscle organized?
Smooth muscle is organized in two ways: as single-unit smooth muscle, which is much more common; and as multiunit smooth muscle. The two types have different locations in the body and have different characteristics. Single-unit muscle has its muscle fibers joined by gap junctions so that the muscle contracts as a single unit.
Why do smooth muscles contract over a wider range of resting lengths?
Smooth muscles can contract over a wider range of resting lengths because the actin and myosin filaments in smooth muscle are not as rigidly organized as those in skeletal and cardiac muscle. Describe the differences between single-unit smooth muscle and multiunit smooth muscle. Single-unit smooth muscle is found in the walls of hollow organs;
What is the size of a smooth muscle fiber?
Smooth muscle fibers are spindle-shaped (wide in the middle and tapered at both ends, somewhat like a football) and have a single nucleus; they range from about 30 to 200 μ m (thousands of times shorter than skeletal muscle fibers), and they produce their own connective tissue, endomysium.
What triggers smooth muscle contraction?
The triggers for smooth muscle contraction include hormones, neural stimulation by the ANS, and local factors. In certain locations, such as the walls of visceral organs, stretching the muscle can trigger its contraction (the stress-relaxation response). Axons of neurons in the ANS do not form the highly organized NMJs with smooth muscle, ...
What is dense body?
A dense body is analogous to the Z-discs of skeletal and cardiac muscle fibers and is fastened to the sarcolemma. Calcium ions are supplied by the SR in the fibers and by sequestration from the extracellular fluid through membrane indentations called calveoli. Because smooth muscle cells do not contain troponin, ...
Why do smooth muscles have low power output?
Because most smooth muscles must function for long periods without rest, their power output is relatively low, but contractions can continue without using large amounts of energy. Some smooth muscle can also maintain contractions even as Ca ++ is removed and myosin kinase is inactivated/dephosphorylated.
What are smooth muscle cells? What are their functions?
Smooth muscle cells are also implicated in atherosclerotic mechanisms. Their proliferation and migration from the media layer to the intima depends on cytokines and growth factors secreted by the endothelial cells, macrophages, lymphocytes and the smooth muscle cells themselves. The contractile genotype of this cell is transformed to a synthetic genotype in the intima and, in these conditions, smooth muscle cells secrete extracellular material, mainly mucopolysaccharides and collagen fibers. This activity, together with their proliferation and elevated vasoconstriction, produces an increase in the volume of the atheromatous plaque and, consequently, an increase in arterial stenosis.
What are the thin filaments in smooth muscle cells?
Smooth muscle cells contain thin (actin) and thick (myosin) contractile filaments as well as cytoskeletal filaments. The thin filaments are the most conspicuous feature of smooth muscle cells. They fill most of the cytoplasm, are easily demonstrable in electron microscopic preparations, are 4–8 nm thick, and insert into condensations ...
What is the function of SMCs?
SMCs are the major cell type of the tunica media and through dynamic cell contraction and relaxation regulate vascular tone and hence, blood flow . The contraction–relaxation state of SMCs is dictated by a spectrum of contractile and cytoskeletal proteins. During embryogenesis, α-smooth muscle actin (SMA) is considered the first SMC marker to be expressed and ultimately is the most abundant protein in SMCs. For instance, the developing pulmonary artery forms in a field of cells expressing the undifferentiated mesenchyme marker platelet-derived growth factor receptor (PDGFR)-β ( Greif et al., 2012 ). Shortly thereafter PDGFR-β + cells adjacent to the nascent EC tube downregulate PDGFR-β and upregulate SMA ( Greif et al., 2012 ). Early developing SMCs also express SM22α (also known as transgelin), which influences the actin cytoskeleton by stabilizing actin filaments. In addition to SMCs, SMA and SM22α are expressed in other cell types as well, whereas smooth muscle myosin heavy chain (SMMHC) and smoothelin are expressed later in SMC differentiation and are generally considered to be specific to the SMC lineage. Yet, our recent studies suggest that SMMHC is also expressed in alveolar myofibroblasts of adult mice exposed to hypoxia ( Sheikh et al., 2014 ).
What are the hollow organs of the body?
Although smooth muscle cells line all hollow organs in the body, including the arteries, gastrointestinal tract, bladder, and uterus, genetic mutations that disrupt SMC-specific isoforms of contractile proteins, along with the mutations in the kinase that controls SMC contraction, lead primarily to vascular diseases.
Where does SMC come from?
Fate-mapping studies have determined that SMCs in the root, arch, and descending regions of the adult aorta derive from the secondary heart field, neural crest, and presomitic mesoderm, respectively ( Majesky, 2007 ).
What type of cell has a spindle shaped nucleus?
Smooth Muscle Cells. Smooth muscle cells are spindle-shaped and have single elongated nuclei. As in cardiac muscle cells, the configuration of the nuclear membranes in smooth muscle cells changes during contraction and relaxation. Smooth muscle cells contain thin (actin) and thick (myosin) contractile filaments as well as cytoskeletal filaments.
Is smooth muscle tone regulation similar to GPCR?
While the basal mechanisms of GPCR-mediated smooth muscle tone regulation are very similar between different organs, the sensitivity of organ-specific smooth muscle cells to smooth muscle regulators can vary profoundly depending on the receptor subtypes expressed by a particular organ-specific smooth muscle cell.
What is the structure of a muscle cell?
Structure of a Muscle Cell. As seen in the image below, a muscle cell is a compact bundle of many myofibrils. Each myofibril is made of many sarcomeres bundled together and attached end-to-end. A specialized form of the endoplasmic reticulum, known as the sarcoplasmic reticulum, extends in and around these myofibril bundles.
What is muscle cell?
A muscle cell, known technically as a myocyte, is a specialized animal cell which can shorten its length using a series of motor proteins specially arranged within the cell. While several associated proteins help, actin and myosin form thick and thin filaments which slide past each other to contract small units of a muscle cell. These units are called sarcomeres, and many of them run end-to-end within a larger fiber called a myofibril. A single muscle cell contains many nuclei, which are pressed against the cell membrane. A muscle cell is a long cell compared to other forms of cells, and many muscle cells connect together to form the long fibers found in muscle tissue.
What happens when myosin heads attach to the actin filament?
This allows the myosin heads to attach to the actin filament. Once this happens, myosin can used the energy gained from ATP to crawl along the actin filament. When many sarcomeres are doing this at the same time, the entire muscle contract.
What is the sarcomere made of?
Each sarcomere is made primarily from thick and thin filaments. Thick filaments are made from repeating units of a protein known as myosin. Myosin has small heads on it which can bind to an actin filament. Repeating units of the protein actin make up the thin filament.
What makes up the thin filament of a muscle?
Repeating units of the protein actin make up the thin filament. Actin is supported by a number of accessory proteins which give the strands stability and allow the muscle to be controlled by nerve impulses. The actin filaments are supported on each end by specialized proteins.
Which protein connects the Z plates together and prevents the sarcomere from being overstr
Another large protein, titin, connects the Z plates together and prevents the sarcomere from being overstretched when it is not contracting. These proteins cannot be seen in the image below. Actin is covered by two additional proteins, troponin and tropomyosin.
What is the mitochondrion?
Mitochondria are densely packed throughout muscle cells, to provide a constant flow of ATP. The entire cell is covered in a specialized cell membrane known as the sarcolemma. The sarcolemma has special opening which allow nerve impulses to be passed into transverse tubules. Below is a blown up view of each sarcomere.
How do smooth muscle cells contract?
As smooth muscle cells have an elongated shape, they can fit together in an arrangement in which the middle portion, which is the widest, tucks in next to the thin end of the neighboring cells. Some of the cells have ends that are split in two. Some smooth muscle cells contract individually, whereas others contract as a group. The cells typically form a sheet wrapping around a hollow center; when they contract, they make the hollow center constrict. For example, when smooth muscle sheets surround an artery, contraction makes the interior of the artery smaller, and relaxation helps the artery dilate.
What is smooth muscle?
Unlike other types of muscle, smooth muscle does not have a stripy appearance, or striations , when viewed under the microscope. This is why this type of muscle is called "smooth." All muscles need a skeleton of fibers that can contract and relax, and in all muscle types, proteins called actin and myosin form this skeleton. When you can see stripes under the microscope, it means the actin and myosin are arranged in a specific, regular pattern called myofibrils, which appear as stripes. According to "Wheater's Functional Histology," smooth muscle does not have myofibrils. Instead, the actin and myosin are arranged in a lattice shape throughout the cell. This lattice shape means that as the cells contract, they get smaller and less elongated in all directions. This allows the sheet of muscle that contains them to wrap tightly and evenly around a hollow center of an artery, for example.
What are some examples of smooth muscle?
Examples include the stomach, intestines, womb, bladder and blood vessels, and it also controls the opening and closing of the pupils of the eye. Generally, smooth muscle has to be able to contract continuously at a low level of intensity. The structure of smooth muscle enables it to function in this manner and differentiates it from other types ...
What are some examples of organelles in the center of a cell?
Examples of organelles found in the center of the cell include mitochondria -- the energy powerhouses of the cells -- and rough endoplasmic reticulum, where newly formed proteins are stored. Golgi apparatus, where proteins are modified, are also in this area, along with polyribosomes, which build proteins.
Where is the nucleus located in a muscle cell?
The nucleus of a smooth muscle cell, which contains the DNA, is located in the center of the cell, where the cell is widest. In the vicinity of the nucleus are various organelles, which are individual structures with specific cell functions. Examples of organelles found in the center of the cell include mitochondria -- the energy powerhouses of the cells -- and rough endoplasmic reticulum, where newly formed proteins are stored. Golgi apparatus, where proteins are modified, are also in this area, along with polyribosomes, which build proteins.
Does smooth muscle have myofibrils?
According to "Wheater's Functional Histology," smooth muscle does not have myofibrils. Instead, the actin and myosin are arranged in a lattice shape throughout the cell. This lattice shape means that as the cells contract, they get smaller and less elongated in all directions.
Do smooth muscle cells contract individually?
Some smooth muscle cells contract individually, whereas others contract as a group. The cells typically form a sheet wrapping around a hollow center; when they contract, they make the hollow center constrict. For example, when smooth muscle sheets surround an artery, contraction makes the interior of the artery smaller, ...
