Muscle Tissue

• Characteristic of Muscle Tissue:

  • ability to contract (body movement)
  • cells that optimize the universal cell property of contractility
  • They are mesodermal origin with abundant synthesis of the myofibrillar proteins actin and myosin
• What do you call the cytoplasm of muscle cells?

  sarcoplasm
• What is the smooth endoplasmic reticulum of muscle?

  sarcoplasmic reticulum
• What is the cell membrane and external lamina of muscle tissue?

  sarcolemma
• Three types of muscle tissue:

  1. Skeletal muscle
  2. Cardiac muscle
  3. Smooth muscle
• Why there are alternating light and dark bands?

  thick and thin filament arrangement
• General characteristic of skeletal muscle:

  • Single multinucleated cells with cross striations
  • Quick, forceful, voluntary contractions
  • Cylindrical with diameter of 10-100 micrometer
  • Striations: present
  • Major locations: skeletal muscle, tongue, diaphragm, eyes and upper esophagus
  • Efferent innervation: motor
  • Involves satellite mainly
• How skeletal muscle is developed?

  1. During embryonic muscle development, mesencyhmal myoblasts fuse forming myotubes
  2. Myotubes then further differentiate to form striated muscle fibers
  3. Sattelite cells proliferate and produce new muscle fibers with injury
• Layers of Connective tissue in all types of muscle; seen well in skeletal muscle:

  1. Epimysium
  2. Perimysium
  3. Endomysium
  4. Deep fascia
• What is epimysium?

  External sheath of dense irregular connective tissue surrounds the entire muscle.
• What is perimysium?

  thin connective tissue layer that surrounds each bundle of muscle fibers termed a fasicle
• What is endomysium?

  Delicate layer of reticular fibers tissue surrounding external lamina of individual muscle fibers.
• What is deep fascia?

  dense irregular connective tissue overlying epimysium
• It joins the muscle to bone, skin or another?

  Myotendinous junctions
• Dark bands are called?

  A bands (Anisotropic Band)
• Light Bands are called?

  I bands (Isotropic Bands)
• Organization within muscle fibers:

  • Sarcoplasm is highly organized, containing primarily long cylindrical filament bundles called myofibrils.
  • I bands are bisected by a dark transverse line, the Z disc.
  • The repetitive functional subunit of the contractile apparatus, the sarcomere, extends from z disc to z disc
• long cylindrical filaments are called?

  myofibrils
• A and I banding pattern in sarcomeres is due to?

  regular arrangement of thick and thin myofilaments composed of F-actin and myosin
• Thick myofilament are composed of?

  myosin; occupy the A bands
• Thin filaments are composed of?

  actin, tropomyosin, F-actin and troponin; occupy the I band
• It contains the binding site for the thick filaments

  G-actin
• Troponin has 3 subunits:

  1. Tnt: attaches tropomyosin
  2. TnI: regulates actin myosin
  3. TnC: binds calcium
• Myosin heads bind both actin, forming transient cross-bridges between the thick and thin filaments and ATP, catalyzing energy release.

  
  

  I bands consist of the portions of the thin filaments which do not overlap the thick filaments in the A bands.
• It support and connect Z discs to the thin filaments

  Alpha actinin
• It binds to z discs to the thick filaments and the largest.

  titin
• 1. A bands contain the both thick filament and overlapping portion of thin filament.
  2. H zone: the lighter zone, it has rodlike protions of the myosin molecule with no thin filaments
  3. M line: contains myomesin and creatine kinase
  4. ATP: soul for muscle contraction
• Myosin binding protein that holds the thick filament in place

  myomesin
• Catalyze the formation of phosphocreatine

  creatine kinase
• Sarcoplasmic Reticulum

  • membranous smooth ER in skeletal and muscle tissue
  • Calcium-ion-sequestration
• Transverse or T-tubules

  • long fingerlike invaginations of the cell
  • aligned A and I band boundaries of sarcomere
• It is expanded structures adjacent to each T-tubule

  Terminal cisternae
• Mechanism of Contraction

  1. Nerve impulse triggers release of Acetyl choline from the synaptic knob into synaptic cleft

  2. Ach binds to Ach receptors initiating muscle impulse in the sarcolemma

  3. Muscle impulse spreads quickly from the sarcolemma along T tubules

  4. Calcium ions released from terminal cisternae into the sarcoplasm

  5. Calcium ions bind to troponin, troponin changes shape and myosin heads of thick filaments attached to exposed active sites

  6. Myosin heads pivot, moving thin filaments toward the sarcomere

  7. ATP binds myosin heads and broken down ADP and P

  8. Myosin heads detach from thin filament, sarcomere shortens and the muscle contracts

  9. When the impulse stops, calcium ions are actively transported into the sarcoplasmic reticulum

  10. Tropomyosin re-covers active sites
• What is the other term of Type I skeletal muscle fibers?

  Slow oxidative fiber
• Type 1 (Slow oxidative fiber)

  • small fibers
  • appear red
  • contains many mitochondria and large amounts of myoglobin and cytochrome
  • Slow-twitch fatigue-resistant motor units
  • Seen in postural muscles for example neck and spine
• Type II A (Fast oxidative Glycolytic Fibers)

  • Intermediate fibers
  • Medium size
  • Many mitochondria and high myoglobin
  • Fast-twitch fatigue-resistant motor
  • Generate high-peak muscle tension
  • intermediate between fast and slow fibers
  • Uses both aerobic and anaerobic metabolism
  • For movements example walking and sprinting
  • Requires more energy than postural control but less energy
• What is the other term for Type II A?

  Fast Oxidative Glycolytic Fibers
• What is the other term for Type II B?

  Fast Glycolytic Fibers
• Fast-twitch fatigue-resistant motor?

  Type II A
• Fast-twitch fatigue-prone motor units?

  Type II B