Chapter 10 Highlights Flashcards
Myocyte
Muscle cell
Sarcoplasm
Myocyte cytoplasm
Sarcolemma
Myocyte plasma membrane
Sarcoplasmic Reticulum (SR)
- Modified endoplasmic reticulum
- Forms web-like network surrounding myofibrils
- Varies in structure in three types of muscle tissue
- Stores and released calcium ions
Myofibrils
- Bundles of specialized proteins
- Allow for contraction
Composition of skeletal muscle tissue
Fibers and endomysium
Skeletal muscle (organization)
- Surrounded by epimysium
- Contains muscle fascicles
Muscle fascicles (organization)
- Surrounded by perimysium
- Contains muscle fibers
Muscle fibers (organization)
- Surrounded by endomysium
- Contains myofibrils
Myofibrils (organization)
- Surrounded by sarcoplasmic reticulum
- Contains sarcomeres (Z line to Z line)
Sarcomere
- Contains thick and thin filaments
Transverse tubules
- Deep inward extensions of sarcolemma
- Surrounds each myofibril
- Continuous with exterior of cell
- Filled with extracellular fluid
Terminal cisternae
- Enlarged sections of SR
- Flank each t-tubule
Triad
Two terminal cisternae plus corresponding t-tubule
Thick filaments
- Myosin
- Binds to actin
Thin filaments
Actin, tropomyosin, and troponin
Elastic filaments
- Single massive, spring-like structural protein (titin)
- Stabilizes myofibril structure
- Resists excessive stretching
Tropomyosin
- Long, rope-like regulatory protein
- Twists around actin, covering up active sites
Troponin
- Small globular regulatory protein
- Holds tropomyosin in place
- Assists with turning contractions on and off
I band
Only thin filaments
Z disc
- In middle of I band
- Structural proteins that anchor thin filaments in place and to one another
A band
- Zone of overlap
- Both thick and thin filaments
- Generate tension during contraction
H zone
Middle of A band where only thick filaments exist
M line
- Dark line in the middle of A band
- Structural proteins hold thick filaments in place
- Serve as anchoring point for elastic filaments
Steps of sliding filament cycle
- Action potential reaches the SR and calcium is released
- Calcium binds to troponin
- Troponin moves, moving tropomyosin and exposing actin active site
- Myosin hinges, myosin head forms cross bridge with actin and moves actin towards the M line, eliminating H zone and I band
- ATP allows release of cross bridge and leaves myosin reenergized
- Calcium (80%) is pumped back to the SR
What happens to I band during contraction?
Narrows
What happens to H zone during contraction?
Narrows
What happens to A band during contraction?
Unchanged
What does myosin attach to?
Actin
What does myosin do to the myofilaments?
Myosin pulls thin filaments toward M line
What is rigor mortis?
Progressive stiffening of skeletal muscles
When does rigor mortis occur?
3-4 hours after death
Why does rigor mortis occur?
- Pumps that drive Ca back into SR have no more ATP to fuel activity
- Ca remains in cytosol, binds to troponin and initiates contraction
Why does the stiffness of rigor mortis remain?
Muscles cannot relax without ATP, so myosin heads cannot detach from actin
How long does rigor mortis last?
- Contraction remains until myofilament proteins degenerate
- About 48-72 hours after death
