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why are skeletal muscles striated

Why are skeletal muscles striated? it can't be because of the actin and myosin because my book says it's present in all muscle types. So what's the reason?
(edited 10 years ago)
Reply 1
Avatar for tammie94
tammie94
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15
anyone?
I think it is because of the layers of actin and myosin.
Reply 3
Avatar for robawalsh
robawalsh
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Original post by tammie94
Why are skeletal muscles striated? it can't be because of the actin and myosin because my book says it's present in all muscle types. So what's the reason?


It helps if you look at the structure in more detail:

sarcomere02.gif

As you can see, a muscle fibre is made up of a number of 'sections' called sarcomeres, defined as the region between two Z-lines. Within that, you have the A-bands and the I-bands.

Sarcomere.gif

The A-band contains both actin and myosin, whereas the I-band contains only actin. Therefore, the A-band will be darker in colour than the I-band, and so you get a "striated" appearance.
Reply 4
Avatar for tammie94
tammie94
OP
15
Original post by robawalsh
It helps if you look at the structure in more detail:

sarcomere02.gif

As you can see, a muscle fibre is made up of a number of 'sections' called sarcomeres, defined as the region between two Z-lines. Within that, you have the A-bands and the I-bands.

Sarcomere.gif

The A-band contains both actin and myosin, whereas the I-band contains only actin. Therefore, the A-band will be darker in colour than the I-band, and so you get a "striated" appearance.


Would involuntary muscles also have lines on the surface (,obviously not parallel and vertical), I'll upload a picture to show you what I mean.

smooth_muscle_contraction1336592998978.jpg

Would you be able to see these criss-cross lines under a light microscope? Or discontinuous lines or something?
(edited 10 years ago)
Reply 5
Avatar for Pride
Pride
21
Original post by tammie94
Would involuntary muscles also have lines on the surface (,obviously not parallel and vertical), I'll upload a picture to show you what I mean.

smooth_muscle_contraction1336592998978.jpg

Would you be able to see these criss-cross lines under a light microscope? Or discontinuous lines or something?


your textbook should simply say that smooth/involuntary muscle is unstriated on observation under a light microscope. Only skeletal and cardiac are striated.
I think it's the way in which the actin and myosin filaments are arranged differently in smooth muscle cells. In striated muscle, the striped pattern may be more visible because the myofibrils are parallel to each other whereas in smooth muscle they're positioned in more of a cross-cross pattern. Maybe read up on the wiki pagehttp://en.m.wikipedia.org/wiki/Smooth_muscle_tissue

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