Skeletal Muscle Flashcards
What is the basic anatomy of the muscle?
Muscle-> myofiber-> myofibril
What are the components inside a Myofribil?
Myofilaments
What are the myofilaments in a myofibril?
- Actin (“thin filament”)
- Myosin (“thick filament”)
Where is the Z line?
Anchors actin
What and where is the Sarcoplasmic reticulum (SR)?
Ca2+ storage and it is in between the Z lines
What is the Sarcolemma?
- myofiber membrane
- has Na+ and K+ channels
- carries MAP from NMJ to end of the myofiber
What is the transverse tubule (T-tubule)?
- extension of sarcolemma
- carries MAP to the SR of each sarcomere
What is the “Excitation-Contraction Coupling” ?
Ca2+ release:
DHPR= dihydropyridine receptor (LTCC) conformational change-> accessory proteins stimulate RYR-1 (ryanodine receptor) on SR -> Ca2+ release into cytoplasm-> Ca2+ go through SERCA-1 (smooth endoplasmic reticulum Ca2+ pump) into SR
What does the SKM look like at Rest?
troponin/tropomyosin complex covers actin –> block myosin binding sites
When does a crossbridge/powerstroke occur?
when myosin binds actin
What are the 6 steps for Contraction?
- Aalpha motorneuron -AP-> terminal-> increase Pca (P/Q type) -> Ca2+ influx–> ACh release
- Diffuse across cleft–> nmAChR activation-> EPP-> MAP (if EPP>V(T))
- MAP spread-> sarcolemma-> T-tubules
- MAP–> DHPR (LTCC)-> RyR-1 –> increase Pca [Ca2+]SR->[Ca2+]cytosol
- Ca2+ -> troponin/tropomyosin uncovers binding sites-> crossbridges/powerstrokes
- Muscle contracts -> increase tension and/or shortens
What occurs during Relaxation?
- [Ca2+]cytosol–SERCA-1–> [Ca2+]SR
- Myosin unbinds from action
- Troponin/tropomyosin cover myosin binding sites
What are the types of contraction?
- Isometric
- Isotonic
- Mixed contraction
What is Isometric contraction?
- constant length (no shortening during contraction), increases tension
What is Isotonic contraction?
- shortens during contraction; constant tension
