Questions: b. What are the dark regions of the striations, and what are the light regions?

The dark and light regions of striations refer to the appearance of muscle fibers, particularly in skeletal and cardiac muscles, when viewed under a microscope.

1. Dark Regions (A Bands):

   • The dark regions are known as A bands (anisotropic bands).
   • They contain thick filaments made primarily of the protein myosin.
   • These regions appear darker because they overlap with thin filaments (actin), increasing the density.

2. Light Regions (I Bands):

   • The light regions are known as I bands (isotropic bands).
   • They contain thin filaments made primarily of the protein actin.
   • These regions appear lighter because they do not overlap with thick filaments, resulting in less density.

In summary, the dark regions are the A bands with overlapping thick and thin filaments, while the light regions are the I bands with only thin filaments.