Cardiac muscle Flashcards
How is the resting potential maintained? Which ion is sarcolemma more permeable to?
By Na-K pumps pumping 3 Na+ ions out for every 2 K+ pumped in. K+ as channels are open.
What happens when an action potential arrives?
Na+ voltage channels open so Na+ entry depolarises the cell, triggering more Na+ channels to open= positive feedback.
When potential is around +52mV, what happens?
Na+ channels close at same voltage gated K+ channels open- partially repolarises the cell.
What else happens during partial depolarisation? This enables what?
Ca2+ voltage gated channels open at T-tubules resulting in Ca2+ inflow into the cell= L-type Ca2+ channels.
This keeps the membrane depolarised at the plateau value of roughly 0mV.
The Ca2+ ions that influx bind to what? This leads to what?
Ryanodine receptors on SR- releases many Ca2+ ions into the cytoplasm– cross-bridge cycle.
Ca2+ binds to what which causes what?
Ca2+ binding sites on troponin protein inaction filament, troponin changes shape and displaces tropomyosin exposing myosin binding sites.
The myosin head binds to what? Known as what?
Actin filament via binding site- Pi is dropped and ADP remains attached to head.
Cross-bridge formation.
The myosin head drops what to contract? Known as what?
The ADP to pull the actin over the myosin, decreasing Z lines. Power stroke.
What binds to the head to detach it? What in the head hydrolyses the ATP into ADP and Pi ready for the next contraction?
ATP. ATPase.
When does contraction stop?
When cytosolic Ca2+ concentration is restored to its original extremely low resting value.
What appearance does cardiac muscle have? How are adjacent cells joined?
Striated- myosin= thick, actin alone with troponin and tropomyosin= thin filaments.
Via intercalated discs- contain desmosomes and gap junctions.
What is the structure of myosin? How many globular heads?
2 large heavy chains and 4 smaller light chains.
2 heads- long tail.
What is the structure of actin?
Single PPC polymerises with other actin monomers– two intertwined helical chains.
What is the A-band? I-band?
Thick and a few overlapping thin filaments.
Only thin filaments extend to centre from Z-lines- contains tropomyosin and troponin.
What is the H-zone? The M-line?
Contain only thick filaments (myosin.) Centre of H-zone= entirely myosin.
