Why isn't smooth muscle striated?

Answer 1

It's so we can tell the difference!

The reason for the striations in skeletal (and cardiac) muscle is that the proteins are all lined up in rows with the actin and myosin lined up so the Z-lines and all are visible to microscopy. Hence it gives a stripy appearance (striated).

The smooth muscle proteins are all higglety-pigglety and loosely aligned to pull the ends of the muscle cell but not lined up neatly like the striated muscle. Hence the bits are all homogenous looking under the microscopy (ie smooth).

WHY it's like that - well I don't rightly know. It seems to work best so maybe we evolved that way or you can re-ask this question in a religious section.

Answer 2

The source below gives this good explanation of why non-striation is advantageous: "To accommodate substantial stretch and still retain contractility."