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Muscle Tissue (Skeletal Muscle (Organization: Long, muscle fibers, single…
Muscle Tissue
Skeletal Muscle
Organization: Long, muscle fibers, single fibers. Myoblast fusion= fibers form from the fusion of many separate myoblast. Multinucleated. Cells made up of myofibrils. Myofibrils are long chain of tiny contractile units called sacromeres. Sacromere gives skeletal muscle its striated appearance.
Sarcomere: Array of thick (myosin II) and thin (actin) filaments. Similar arrangement in cardiac muscle but not as regular. Smooth muscle not arranged in sarcomeres. Actin filament are coated by tropomyosin and troponin
Muscle histology/EM structure: H&E stain see the striations perpendicular to the long axis of the myofibers. Reveals sacromeric organization
Sarcomere contraction: shortening/contraction is generate by myosin filaments sliding along actin filaments without shortening of either filament. Rapid, synchronized shortening of the sarcomere.
Nueromuscular Junction: specialized chemical synapse between a motor neuron and a skeletal muscle cell. Nicotinic ACh receptors on the motor end plates. ACh binds to ligand gated Na ion channels, Na influx and depolarize the cell. activated Ca channels in the transverse tubules (invaginatoins of the plasma membrane; wrap around the each myofibril) and Ca ion channel open up in the sacroplasmic reticulum.
Troponin: Binds Tropomyosin and F-actin. TN pulls TM out of th actin binding grove and into posotion that Blocks myosin binding to F-actin.
Types of skeletal muscle: 1. Type 1 (Slow twitch)= contract slowly, repeatedly, 2. Type 2a (Fast twich) = contract fast, aerobic/anaerobic energy source, 3. Type 2b (Fast twitch) = Contract extremely fast, anaerobic energy source.
Smooth Muscle
Location: Stomatch, intestine, uterus, and atery walls.
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Lack striations, uninucleated, sheets of elongated spindled-shaped cell. Orientated along different axes. Smooth muscle cells can be physiically and electrically coupled.
Histological features of smooth muscle: Smallest muscle cell, tapered, fusiforme cell shape, uninucleated, non-striated.
Contraction: Intiated by external stimula. Induces influx of Ca. No TN is expresses, Ca binds CaM. Phosphorylation intiated contraction cycle.
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Cardiac Muscle
Cardiomyocytes DO NOT fuse during development. Linked end to end by a specialized adhesive structure called interclaated disc and forms a functional syncytium.
Intercalated Disc = Asherene junctions, demosomes, and gap junctions.
Histological features = Moderately elongated, uninucleated, branched, connected by intercalated disc
Intercalated Disc: AJs and desmosomes link actin and intermediate filameent cytoskeletons. Mutations in ICD= cardiomyopathies
Muscle contration-> Required for movement, transport of blood and nurtients, peristalsis, ATP driven sliding of actin against myosin filaments