Two EK Bio Questions

[golgiapparatus88]

#169 from EK Bio:
During a muscular contraction:
b. The thin filament contracts but the thick filament does not
d. Neither thin or think contract.

Answer is D. I said b because the think filaments grab on to the actin and pull them closer towards the H zone. I see that the A-band would not change size because the myosin isn't moving but to me, we are able to move our body because myosin moves actin, thereby causing the thin filament to move.

#182 EK Bio:
Cardiac muscle is excited by
C. increased cytosolic sodium concentration
D. increased cytosolic calcium concentration

Answer is D again. I chose C because sodium is needed for the initial depolariation followed by slow-Ca2+ channels allowing a slow flux of Ca2+ into the cell causing the plateau period. Why am I wrong?

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[Salient]

169

The filaments are moving past each other, but neither is changing in length.

182

I'd guess just because Calcium causes muscle contraction. Sodium has to do with action potentials, so I think you're just overthinking it.

 

[PiBond]

#169 from EK Bio:
During a muscular contraction:
b. The thin filament contracts but the thick filament does not
d. Neither thin or think contract.

Answer is D. I said b because the think filaments grab on to the actin and pull them closer towards the H zone. I see that the A-band would not change size because the myosin isn't moving but to me, we are able to move our body because myosin moves actin, thereby causing the thin filament to move.

#182 EK Bio:
Cardiac muscle is excited by
C. increased cytosolic sodium concentration
D. increased cytosolic calcium concentration

Answer is D again. I chose C because sodium is needed for the initial depolariation followed by slow-Ca2+ channels allowing a slow flux of Ca2+ into the cell causing the plateau period. Why am I wrong?

169: the muscle is contracting but the thick and thin filaments aren't changing lengths--they are just changing their degree of overlapping.

182: the cardiac muscle is excited by increasing cytoplasmic Ca2+ via our voltage gated calcium channels in the sarcoplasmic reticulum in addition to extracellular Ca2+. this is necessary to bind troponin and move tropomyosin out of the way so we can expose our myosin binding sites. i can see where this is confusing because our depolarization of our membrane is initiated by an influx of Na+, but keep in mind that it is the Ca2+ that ultimately causes muscle contraction.

 

[golgiapparatus88]

169

The filaments are moving past each other, but neither is changing in length.

182

I'd guess just because Calcium causes muscle contraction. Sodium has to do with action potentials, so I think you're just overthinking it.

Thanks, so even though the H-zone and I-bands are reduced, the actual actin and myosin filaments don't change lengths..they are just moved around.

 

[Salient]

Thanks, so even though the H-zone and I-bands are reduced, the actual actin and myosin filaments don't change lengths..they are just moved around.

Correct. If I recall correctly the H and I bands are just the overlapping and non-overlapping regions. So their lengths simply reflect the positions of actin and myosin relative to each other.

 

[phospho]

Correct. If I recall correctly the H and I bands are just the overlapping and non-overlapping regions. So their lengths simply reflect the positions of actin and myosin relative to each other.