Ultrastructural analysis of pale tremor ( plt ) skeletal muscle. Representative photomicrographs from transmission electron microscopic analysis of wild-type/littermate (WT) quadriceps (A) and plt quadriceps (B) and (C). Muscle ultrastructure was generally normal in plt muscle (B) with evidence of normal triads (arrow). There were infrequently observed areas of abnormalities that particularly included swollen and/or dilated mitochondria (M in (C)). Scale bars = 500 nm.