characteristic of cardiac muscle

[MudPhud20XX]

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Alright so probably a low yield question for the board, but I'll ask anyway.

Here is a Kaplan question:

Which of the following is a distinctive characteristic of cardiac muscle?
A. Contains actin and myosin that lack a distinct banding pattern.
B. Cells are linked by gap junctions.
C. Has T tubules situated at the A-I band junction.
D. Has intercalated disks that contain tight junctions.
E. Utilizes the intermediate filament vimentin for structural support.

The answer is B, but isn't gap junctions also a characteristic of smooth muscle too? At least that's what it says in the Kaplan anatomy book. So is it the word "linked" that makes B the answer?

Many thanks in advance.

 

[notbobtrustme]

ugh. This is just an ugly question all around.

Typically, you would associate gap junctions with cardiac muscle because that allows for coordinated contraction of many cardiac muscle fibers, since the electrical single would be free to travel to all muscle cells nearly simultaneously.

 

[Fatalis]

With smooth muscle its not gap junctions, it's dense bodies.

 

[MudPhud20XX]

thanks guys. dense bodies for smooth muscle! Dense bodies act act like Z-line of sarcomere and provide an attachment site for actin microfilaments in smooth muscle.

 

[Fatalis]

you got it man
I knew it bc it was asked on a midterm and it was the tinest blurb on the power point slide lol

 

[scoKraz4]

That is 100% wrong. There is single-unit SM and multi-unit SM. The bladder/uterus consists of single-unit smooth muscle and the fibers are connected via gap junctions. This exist so the muscle can contract in a coordinated fashion... like during parturition. Intercalated discs are a distinct histological feature of cardiac myocytes which would make D the correct answer.

 

[Missorleans]

That is 100% wrong. There is single-unit SM and multi-unit SM. The bladder/uterus consists of single-unit smooth muscle and the fibers are connected via gap junctions. This exist so the muscle can contract in a coordinated fashion... like during parturition. Intercalated discs are a distinct histological feature of cardiac myocytes which would make D the correct answer.

I went for D at first too, but intercalated discs have gap junctions, fascia adherens, and macula adherens, not tight junctions.

 

[CherryRedDracul]

Because both B and D are half-correct, I decided to average the two and go with C.