Information about Sarcomere
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Image of sarcomere
- The thick filament system is composed of myosin protein which is connected from the M-line to the Z-disc by Titin
- The thin filaments are assembled by actin monomers bound to Nebulin.
- Nebulin and Titin gives stability and structure to the sarcomere.
Bands
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Sliding filament model of muscle contraction
- A sarcomere is defined as the segment between two neighbouring Z-lines (or Z-discs, or Z bodies). In electron micrographs of cross striated muscle the Z-line (from the German "Zwischen", between the I bands) appears as a series of dark lines.
- Surrounding the Z-line is the region of the I-band (for isotropic).
- Following the I-band is the A-band (for anisotropic). Named for their properties under a polarizing microscope.
- Within the A-band is a paler region called the H-band (from the German "Heller", bright). Named for their properties under a polarization microscope.
- Finally, inside the H-band is a thin M-line (from the German "Mittel", middle of the sarcomere).
- Actin filaments are the major component of the I-band and extend into the A-band.
- Myosin filaments extend throughout the A-band and are thought to overlap in the M-band.
- The giant protein titin (connectin) extends from the Z-line of the sarcomere, where it binds to the thin filament system, to the M-band, where it is thought to interact with the thick filaments. Titin (and its splice isoforms) is the biggest single protein found in nature. It provides binding sites for numerous proteins and is thought to play an important role as sarcomeric ruler and as blueprint for the assembly of the sarcomere.
- Several proteins important for the stability of the sarcomeric structure are found in the Z-line as well as in the M-band of the sarcomere.
- Actin filaments and Titin molecules are cross-linked in the Z-disc via the Z-line protein alpha-Actinin.
- The M-band proteins myomesin as well as M-protein crosslink the thick filament system (myosins) and the M-band part of titin (the elastic filaments).
- The interaction between actin and myosin filaments in the A-band of the sarcomere is responsible for the muscle contraction (sliding filament model).
Contraction
Upon muscle contraction, the A-bands maintain their length (1.6 micrometer in mammalian skeletal muscle) whereas the I-bands shorten.
The A-band, I-band and Z-line are the only components visible at the light-microscope level.
The protein tropomyosin covers the myosin binding sites of the actin molecules in the muscle cell. To allow the muscle cell to contract, tropomyosin must be moved to uncover the binding sites on the actin. Calcium ions bind with troponin molecules (which are dispersed throughout the tropomyosin protein) and alter the structure of the tropomyosin, forcing it to reveal the cross bridge binding site on the actin. The concentration of calcium within muscle cells is controlled by the sarcoplasmic reticulum, a unique form of endoplasmic reticulum. Muscle contraction ends when calcium ions are pumped back out of the sarcomere.
Skeletal muscle only contracts when an impulse is received from a motor neuron. During stimulation of the muscle cell, the motor neuron releases the neurotransmitter acetylcholine which travels across the neuromuscular junction (the synapse between the terminal bouton of the neuron and the muscle cell). The action potential then travels along T (transverse) tubules until it reaches the sarcoplasmic reticulum; the action potential from the motor neuron changes the permeability of the sarcoplasmic reticulum, allowing the flow of calcium ions into the sarcomere. The outflow of calcium allows the myosin heads access to the actin cross bridge binding sites, permitting muscle contraction.
Rest
At rest, the myosin head is bound to an ATP molecule in a low-energy configuration and is unable to access the cross bridge binding sites on the actin. However, the myosin head can hydrolyze ATP into ADP and an inorganic phosphate ion. A portion of the energy released in this reaction changes the shape of the myosin head and promotes it to a high-energy configuration. Through the process of binding to the actin, the myosin head releases ADP and inorganic phosphate ion, changing its configuration back to one of low energy. The myosin remains attached to actin in a state known as Rigor, until an new ATP binds the myosin head. This binding of ATP to myosin releases the actin by cross-bridge dissociation. The ATP associated myosin is ready for another cycle, beginning with hydrolysis of the ATP.Storage
Most muscle cells only store enough ATP for a small number of muscle contractions. While muscle cells also store glycogen, most of the energy required for contraction is derived from phosphagens. One such phosphagen is creatine phosphate, which is used to provide ADP with a phosphate group for ATP synthesis in vertebrates.External links
- UIUC Histology Subject 524
- Histology at BU 21601ooa - "Ultrastructure of the Cell: sarcoplasm of skeletal muscle"
- Mnemonic at medicalmnemonics.com 50 379 107|
- Images created by antibody to striations
- model of a sarcomere
Histology: muscle tissue | |
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| skeletal muscle/general | epimysium, fascicle, perimysium, endomysium, muscle fiber (intrafusal, extrafusal), myofibril sarcomere (a, i, and h bands; z and m lines), myofilaments (thin filament/actin, thick filament/myosin, elastic filament/titin, nebulin), tropomyosin, troponin (T, C, I) costamere (dystrophin, α,β-dystrobrevin, syncoilin, synemin/desmuslin, dysbindin, sarcoglycan, dystroglycan, sarcospan), desmin neuromuscular junction, motor unit, muscle spindle, excitation-contraction coupling, sliding filament mechanism myoblast, satellite cell, sarcoplasm, sarcolemma, sarcoplasmic reticulum, T-tubule |
| cardiac muscle | myocardium, intercalated disc, nebulette |
| smooth muscle | calmodulin, vascular smooth muscle |
MUSCLE (multiple sequence comparison by log-expectation) is public domain, multiple sequence alignment software for protein and nucleotide sequences.
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Myofibrils (obsolete term: sarcostyles) are cylindrical organelles, found within muscle cells. They are bundles of actomyosin filaments that run from one end of the cell to the other and are attached to the cell surface membrane at each end.
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Myosins are a large family of motor proteins found in eukaryotic tissues. They are responsible for actin-based motility.
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Structure and Function
Domains
Most myosin molecules are composed of both a head and a tail domain...... Click the link for more information.
Not to be confused with Tintin.
Titin, also known as connectin[1] (UniProt name: Q10466_HUMAN; accession number: Q10466), is a protein that is important in the contraction of striated muscle tissues.
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Actin is a globular structural, 42-47 kDa protein found in many eukaryotic cells, with concentrations of over 100 μM. It is also one of the most highly conserved proteins, differing by no more than 5% in species as diverse as algae and humans.
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Nebulin is an actin-binding protein which is localized to the I-band the sarcomeres in skeletal muscle. It is a very large protein (600-900 kDa) and binds as many as 200 actin monomers.
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muscle fiber, also spelled muscle fibre (see spelling differences), also technically known as a myocyte, is a single cell of a muscle. Muscle fibers contain many myofibrils, the contractile unit of muscles.
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- For other uses, see biceps.
In human anatomy, the biceps brachii is a muscle located on the upper arm. The biceps has several functions, the most important simply being to flex the elbow and to rotate the forearm.
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Smooth muscle is a type of non-striated muscle, found within the "walls" of hollow organs and elsewhere like the bladder and abdominal cavity, the uterus, male and female reproductive tracts, the gastrointestinal tract, the respiratory tract, the vasculature, the skin and the
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German language (Deutsch, ] ) is a West Germanic language and one of the world's major languages.
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Isotropy (the opposite of anisotropy) is the property of being independent of direction. Isotropic radiation has the same intensity regardless of the direction of measurement, and an isotropic field exerts the same action regardless of how the test particle is oriented.
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Anisotropy (pronounced with stress on the third syllable, IPA: /ˌænaɪˈsɒtrəpi/) is the property of being directionally dependent, as opposed to isotropy, which means homogeneity in all directions.
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Not to be confused with Tintin.
Titin, also known as connectin[1] (UniProt name: Q10466_HUMAN; accession number: Q10466), is a protein that is important in the contraction of striated muscle tissues.
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A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten or remain the same.
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A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten or remain the same.
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The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. It is a chemical transmitter in both the peripheral nervous system (PNS) and central nervous system (CNS) in many organisms including humans.
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Adenosine 5'-triphosphate (ATP) is a multifunctional nucleotide that is most important as a "molecular currency" of intracellular energy transfer. In this role, ATP transports chemical energy within cells for metabolism.
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phosphagens are energy storage compounds, also known as high energy phosphate compounds, are chiefly found in muscular tissue in animals. They allow a high energy phosphate pool to be maintained in a concentration range which, if it all were ATP, would create problems due to the
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Phosphocreatine, also known as creatine phosphate or Pcr, is a phosphorylated creatine molecule that is an important energy store in skeletal muscle. It is used to anaerobically generate ATP from ADP, forming creatine for the 2 to 7 seconds following an intense
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The College of Medicine at Urbana-Champaign is a graduate school at the University of Illinois at Urbana-Champaign.The UIC College of Medicine at Urbana-Champaign is located at the original campus of the University (with 42,000 students, undergraduate and graduate) and offers a
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Boston University (BU) is a private research university located in Boston, Massachusetts, United States. Although chartered by the Massachusetts Legislature in 1869, Boston University traces its roots to the establishment of the Newbury Biblical Institute in Newbury,
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Not to be confused with pneumonic.
A mnemonic (pronounced IPA: /niːˈmɒnɪk/ in RP, /nɨˈmɑnɨk/
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Histology (from the Greek ἱστός) is the study of tissue sectioned as a thin slice, using a microtome. It can be described as microscopic anatomy.
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MUSCLE (multiple sequence comparison by log-expectation) is public domain, multiple sequence alignment software for protein and nucleotide sequences.
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Skeletal muscle is a type of striated muscle, usually attached to the skeleton. Skeletal muscles are used to create movement, by applying force to bones and joints; via contraction.
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Epimysium is a layer of connective tissue which ensheaths the entire muscle. It is composed of dense irregular connective tissue. It is continuous with fascia and other connective tissue wrappings of muscle including the endomysium, and perimysium.
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In anatomy, a fascicle is a bundle of skeletal muscle fibers surrounded by connective tissue.
Specialized muscle fibers in the heart which transmit electrical impulses from the Atrioventricular Node (AV Node) to the Purkinje Fibers are fascicles, also referred to as bundle
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Specialized muscle fibers in the heart which transmit electrical impulses from the Atrioventricular Node (AV Node) to the Purkinje Fibers are fascicles, also referred to as bundle
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