muscle type

[sdnstud]

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I thought this question was kinda strange, can someone explain this:

All of the following are true concerning smooth muscle except:
A. the main contributor to depolarization during action potential is Ca2+ channels
B. does not contain sarcomeres
C. Contains actin and myosin
D. is straited.

The answer is obviously D. However, I thought C could be correct also. Does smooth muscle contain actin and myosin? if smooth muscle does not contain sarcosmeres...then it shouldn't have actin and myosin right?

I think this question is a typo...it's probably asking about cardiac muscle...in that case...the answer is B...and it makes lotsa sense

 

[willthatsall]

Nah, I think it is alright. The sarcomeres give striated muscle it's patterned appearance. The smooth muscle lacks the organization of sarcomeres, but it still contains actin and myosin. I think it's safe to say that ALL muscle has actin and myosin.

 

[MDtoBe777]

No, I think it is right. Smooth muscle has actin and myosin. However, they are not arranged in a sarcomere structure. So this is why C is true.

 

[MDtoBe777]

Question about this: Smooth muscle does not require the T-tubules right? since it is so thin and depolarization at the membrane is sufficient to depolarize the cell.

 

[ASDIC]

remember smooth muscle cells look smooth because they have striations.

 

[Dr. N]

I thought this question was kinda strange, can someone explain this:

All of the following are true concerning smooth muscle except:
A. the main contributor to depolarization during action potential is Ca2+ channels
B. does not contain sarcomeres
C. Contains actin and myosin
D. is straited.

The answer is obviously D. However, I thought C could be correct also. Does smooth muscle contain actin and myosin? if smooth muscle does not contain sarcosmeres...then it shouldn't have actin and myosin right?

I think this question is a typo...it's probably asking about cardiac muscle...in that case...the answer is B...and it makes lotsa sense

I don't agree that it is a typo. any cell contains actin and myosin, so smooth muscle cell as well. I did not read other people answers, maybe somebody already said that

 

[Dr. N]

Nah, I think it is alright. The sarcomeres give striated muscle it's patterned appearance. The smooth muscle lacks the organization of sarcomeres, but it still contains actin and myosin. I think it's safe to say that ALL muscle has actin and myosin.

I think it is safe to say that ALL CELLS have actin and myosin as a part of cytoskeleton

 

[VPDcurt]

Actin is part of the cytoskeleton but myosin is not. Myosin is has intrinsic ATPase activity and is found in all muscle cells. However, it does not form thick filaments in smooth muscle (only cardiac and skeletal). Smooth muscles lacks troponin and tropomysosin and uses MLCKs activated by calmodulin in the presence of calcium. Moreover, smooth muscle is not striated so the answer is D.

 

[safrat]

The reason there CARDIAC and SKELETAL muscles have straition is that they have their actin and mysin in units called sarcomeres. Thus, the sarcomeres themselves are what give muscles the appearance of being straited.

Now, smooth muscles do have T-tubules, however, they don't rely on Ca2+ concentration, as opposing to cardiac and skeletal, b/c they are so thin that the Na+ causing the depolarization is enough to cause an action potention in the ENTIRE cell not just the outer membrane.

If the OP is using the TPR books, then refer to chapter 8. It specifies all the characteristics of muscles.

 

[VPDcurt]

Smooth Muscles do NOT have T - Tubules. The cell is so small they they are not required.

 

[safrat]

oh sorry, yeah, you're right, but the straition part is right.

 

[Fusion]

Smooth muscle has both actin and myosin, just a whole hell of a lot more actin than myosin. This may seem weird, given what we know about striated muscle. But the way the smooth muscle cell is structured is the reason why its proportion of actin to myosin is so high.

Also, remember that smooth muscle cells have dense bodies, no T-tubules, and Ca2+ binds to calmodulin which, as a complex, stimulates MLCK, which phosphorylizes the filaments and causes contraction. Smooth muscle cells exist primarily in arteries/arterioles and the GI tract. Contraction is much slower in comparison to skeletal or cardiac myocytes.