It looks to me like your nerve tissue lanes have a lot more bands compared to the heart tissue ones, with fewer majority bands. Even though you've loaded theoretically the same amount, if there are many more protein types in the nerve tissue then the staining intensity per band will differ as the dye will have to bind to more proteins (plus even "total" stain dyes will preferentially bind more to some proteins compared with others). As they are different tissue types, they will look different anyway, so it is difficult to really make comparisons.

You need to do some sort of quantification by either total protein normalisation (using ImageJ/Fiji or similar on your Ponceau stained membranes) or by immunoblotting for a housekeeping protein like GAPDH, actin etc and quantifying the band density. Doing a rough total protein normalisation on the top membrane image that you have attached and normalising against the heart tissue in lane 2 suggests that you have loaded similar amounts of total protein for the nerve and heart tissues (at least for the first few lanes, afterwards it breaks down a bit, likely because the lighting in the photo you attached isn't completely even).

It is unlikely that there are many free lipids in your sample by the time you reached the stage of the BCA assay, as the detergents in the RIPA buffer will have formed micelles with the lipids.