Unit 8: Muscle Physiology Flashcards
During embryonic development, huge skeletal fibres are formed by fusion of what component?
Myoblasts
What are the contractile elements of skeletal muscle?
Myofibrils
*Consist of thick and thin filaments
What protein make up thick filaments?
Myosin
What proteins make up thin filaments?
Actin
What are the 2 man components of connective tissue that covers muscle?
Collagen & Elastin
What are the 3 layers of connective tissue?
- Epimysin
- Perimysin
- Endomysin
What is a dark (A band) ?
- Arranged of stacks of thick filaments along thin filaments that overlap the ends of the thick filaments.
- Contains an M line, a series of proteins that holds the thick filaments in place.
What is the H zone of an (A band)?
-Contain an H zone (middle ear of the A band- that has no thin filaments)
What is a light I Band?
-Consists of thin filaments that do not project into the A band.
What is a Z line?
–>The middle of each I band has a vertical Z line, and the area between the 2 Z lines is called a sacromere, the functional unit of skeletal muscle.
What are the 2 crucial sites needed for myosin-actin interaction?
1) Actin-myosin binding site
2) Myson ATPase site (ATP splitting)
What are the 3 thin filament proteins?
1) Actin
2) Tropomyosin
3) Troponin
Why can’t muscle contraction occur in a relaxed muscle?
-Tropomyosin and troponin block the binding site.
Basic muscle contraction process.
The binding of Troponin to Ca2+ which allows for the movement of tropomyosin, no longer blocking the binding site. This allows actin and myosin to bind, and the muscle can contract.
What is the sliding filament mechanism?
-The THIN FILAMENTS SLIDE INWARD, over the thick filaments, towards the A bands center during contraction.
Z lines are pulled closer together, and sacromeres shorten.
*All sacromere’s shorten at once, and the muscle fibre simultaneously shortens.
->Known as concentric contraction
*Thick filaments remain unchanged.
What are the mechanisms of a Power Stroke?
When actin and myosin make contact at a cross bridge, the bridge changes shape- bending inward towards the sacromere like the stroking of an oar.
- The power stroke pulls thin filaments inward.
- repeated cycles complete the shortening process.
How is an actin-myosin interaction stopped?
-At the end of the cross bridge, the myosin-actin link breaks. The cross bridge returns to its original shape, ready for another actin to bind the myosin head.
What is the term “excitation-contraction” for muscles?
excitation- generation of action potentials in the muscle fibre
contraction- actin-myosin binding that causes sacromeres to shorten
What are Transverse Tubules (T Tubules) ?
Carry action potentials generated throughout the muscle fiber
What is the Sarcoplasmic Reticulum?
-Segments are wrapped around each A/I band, and have sac like regions called LATERAL SACS.
What are Lateral Sacs?
-Store calcium, and a spread of an action potential down a T tubule leads to the release of calcium from the sarcoplasmic reticulum into the cytosol.
What is the role of Calcium in the contraction of muscles?
Ca2+ is what moves tropomyosin during cross bridge activity, allowing actin and myosin to bind.
How is the myosin ATPase site involvement in the myosin-actin cross bridge?
- The breakdown of ATP occurs before actin and myosin meet.
- Pi and ADP are released (ATP is used) when the myosin and actin interaction occurs, after calcium has been released.
- ->When Pi and ADP are released, the myosin ATPase site is free for attachment of another ATP molecule.
- This allows for the bending back of the cross bridge and the cycle can continue.
How does the cycle continue ?
The new bound ATP is split by ATPase, energizing the myosin cross bridge once again, and on binding with another actin, the cross bridge bend to make a power stroke, and so on.