Lesson 3 Flashcards
What is muscle comprised of?
75% water
20% protein
Where is 50-75% of protein stored? What is that fact important when we are sick?
skeletal muscle
-amino acids in muscle become a big reserve for WBC production when sick
Describe skeletal muscle organization briefly.
myofilament (actin and myosin) -> sarcomere (contractile unit) -> myofibrils (sarcomeres in series) -> muscle fiber cells -> muscle fascicle -> whole muscle
What are costameres?
- proteins that coordinately transduce contractile F from Z-line to basement membrane laterally, where it can then transmit F parallel to muscle cells’ long axis (become tensioned during contraction of sarcomere and transmit F to basement membrane)
- 3 different cytoskeletal networks form costameres: integrin, spectrin, and dystroglycan
What happens in muscular dystrophy?
dystrophin impaired (another costamere) which destroys the muscle fibers
Where are intermediate filaments and what do mutations cause?
- between myofibrils and form network around Z disks to keep sarcomeres in line
- fragility with muscle contraction
Where does Titin run? What is PEVK’s role in Titin?
- Titin runs from Z-line past myosin and has passive tension that can contribute to F production w/ sarcomere sliding/stretching
- PEVK allows Titin to stretch b/c wound up and can unravel to provide passive tension to Titin
- Titin helps guid/control sarcomere sliding
In the troponin-tropomyosin-actin complex, where is the tropomyosin and what does each troponin bind?
tropomyosin: “tail of myosin” spans 7 G-actin molecules
troponin:
T binds tropomyosin
I binds G-actin
C binds 4 calcium ions
Describe myosin structure and function.
- thick filament with tail and globular head
- globular head has 3 functions: 1) light chain responsible for speed of ATP hydrolysis on MHC 2) actin-binding 3) ATP-binding at ATP pocket; if pocket has no ATP, there is no binding to ATP
How does the myosin head play a role in Rigor Mortis?
ATP isn’t being hydrolyzed and is stuck in ATP pocket, so myosin bound to actin
What does the M line do? In which muscle fiber is it thickest?
- stabilizes thick-filament lattice
- thicker in Type 1 (decreased F producing) > Type II fast twitch
Describe the overview of muscle contraction.
1) AP to motor neuron
2) AP propagates to pre-synapse, causing Calcium channels to open
3) Calcium flux causes vesicle emptying of ACh into synaptic drift
4) ACh diffuses to post-synapse and binds to ACh R’
5) Causes an increase in sodium/K permeability to depolarize muscle cell and create AP
6) AP travels in all directions through T-tubules, but diminishes as AP travels further into muscle cell (which is why Type II fibers are on the surface)
7) AP activates dihydropyridine R’ in T-tubule
8) DHP R’ physically connected to Ryanodine R’ in sarcoplasmic reticulum and causes SR to release calcium into cytosol
9) Calcium binds to C-subunit of troponin, which moves Tropomyosin away from F-actin binding site
10) myosin binds to actin, creating a cross bridge and muscle contraction follow in presence of ATP to ADP
11) APT then binds to myosin to release cross-bridge
Does the Type I or Type II fibers has higher threshold for stimulation.
Type I takes less depolarization as AP travels down T-tubule
How does chemo-mechanical coupling work in the SR? What is the Triad?
- voltage-sensitive DHP receptors on the T-tubule are activated, which causes conformational change on Ryanodine R’ on the SR to release calcium
- calcium binds to troponin and actin-myosin crossbridge forms (mechanical E)
How much does 1 myosin head produce in force?
4-6 pN w/ no gender difference
