MUSCLE TISSUE

• Muscle cells are of mesodermal origin and differentiate by a gradual process of cell lengthening with abundant synthesis of the myofibrillar proteins actin and myosin
• What is the cytoplasm of muscle cells?

  sarcoplasm
• What is the smooth er of muscle?

  Sarcoplasmic reticulum
• What is the cell membrane and external lamina?

  Sarcolemma
• Cardiac muscles

  • Contains cross striations elongated branched cells bound to one another at structure transverse line called intercalated discs which is unique to cardiac muscle
  • Contraction is involuntary, vigorous and rhytmic
• Smooth muscle

  • Fusiform cells with lack of striations
  • Slow, involuntary contractions
• Development of the skeletal muscle

  1. During embryonic muscle development, mesenchymal myoblast fuse, forming myotubes with many nuclei
  2. Myotubes then further differentiate to form striated muscle
  3. Sattelite cells proliferate and produce new muscle fibers following muscle injury. It is from myoblast that does not undergone differentiation and fuse.
• It is an external sheath of dense irregular connective tissue?

  Epimysium
• It surrounds the entire muscle?

  Epimysium
• Thin connective tissue layer that surrounds each bundle of muscle fibers termed a fascicle?

  Perimysium
• delicate layer of reticular fiber tissue surrounding the external lamina of individual muscle fibers?

  Endomysium
• Dense irregular connective tissue overlying epimysium?

  Deep Fascia
• Join the muscle to bone, skin or another muscle?

  Myotendinous junctions
• Dark Bands are A bands (Anisotropic Band)

  Light Bands are I bands (Isotropic Band)
• Sarcoplasm is highly organized, containing primarily long cylindrical filament bundles called myofibrils
• I bands are bisected by a dark transverse line, the Z disc
• Z disc to Z disc = 1 sarcomere
• The repetitive functional subunit of the contractile apparatus, the sarcomere, extends from Z disc to Z disc
• The A and I banding pattern in sarcomeres is due to to regular arrangement of thick and thin myofilaments, composed of myosin and F-actin.
• Thick myofilament- consist of Myosin; occupy the A bands
• Thin filament- consist of actin, tropomyosin, F-actin, and troponin; occupy the I bands
• Contains the binding site of the thick filament (myosin)?

  G-actin
• Troponin has 3 subunits:

  • TnT- attaches to the tropomyosin
  • TnI- regulated actin-myosin interaction
  • TnC- bind calcium
• Myosin heads bind both actin, forming transient cross-bridges between thick and thin filaments, and ATP catalyzing energy release (actomyosin ATPase activity)
• I bands consist of the portion of the thin filaments which do not overlap the thick filaments in the A band
• connects Z discs to the thin filaments?

  Alpha actinin
• connect Z discs to the thick filaments and consider largest protein in our body?

  Titin
• A bands contain both the thick filaments and the overlapping portions of thin filaments
• H zone

  • Ligther zone
  • Has rod-like portions
  • no thin filaments
• M Line

  Consist myomesin (myosin binding protein that hold thick filaments in place); contain creatine kinase (catalyzes the formation of phosphocreatine- storage for high energy phosphate)
• soul for muscle contraction?

  ATP
• membranous smooth ER in skeletal muscle fiber?

  Sarcoplasmic reticulum
• For calcium-ion-sequestration?

  Sarcoplasmic reticulum
• Long fingerlike invaginations of the cell membrane encircling each myobril near the aligned A and I band boundaries of sarcomeres?

  Transverse or T-tubules
• Expanded structures adjacent to each T-tubule?

  Terminal cisternae
• Contraction occurs on the overlapping of the thin filaments
• Muscle Contraction

  1. Nerve impulse triggers release of Acetyl Choline from synaptic knob to synaptic cleft

  2. AcH bind to AcH receptor in motor end plate, initiating muscle impulse in sarcolemma

  3. Muscle impulse spreads along T tubules, calcium ions released from terminal cisternae into sarcoplasm

  4. Calcium ions bind to troponin

  5. Troponin changes shape, moving tropomyosin to expose actin active sites

  6. Myosin heads attach to exposed actin active sites, forming cross-bridges

  7. Myosin heads pivot, moving thin filaments toward sarcomere center

  8. ATP binds myosin heads and is broken down into ADP and P

  9. Myosin heads detach from thin filaments, sarcomere shortens, muscle contracts

  10. When impulse stops, calcium ions transported into sarcoplasmic reticulum

  11. Tropomyosin re-covers actin active sites, filaments slide back to relaxed state
• Different type of fibers can be identified on the basis of

  1. Their maximal rate of contraction (fast or slow fibers)
  2. Their major pathway for ATP synthesis (oxidative phosphorylation or glycolysis)
• Type I is also known as?

  Slow oxidative fibers
• Type II A is also known?

  Fast oxidative glycolytic fibers