Muscle-fiber architecture, innervation, and histochemistry in the diaphragm of the cat.

Previous anatomical descriptions of the diaphragm have contained several contradictory findings. To validate and extend the previous work, diaphragmatic architecture, histochemistry, and end-plate distribution were examined by use of a combination of anatomical methods, including fiber microdissections, cholinesterase staining, and enzyme histochemistry. Microdissections showed that muscle-fiber fascicles throughout the diaphragm contain both long fibers that run from origin to insertion and shorter fibers with intrafascicular terminations. Fibers with intrafascicular terminations were particularly common in the costal diaphragm, where they accounted for the majority of sampled fibers. The heterogeneity of fiber length was reflected in the pattern of end-plate banding. Cholinesterase studies showed that fiber fascicles in cat and kitten diaphragms were crossed by two to four end-plate bands distributed in discontinuous arrays across the width of the muscle. A similar pattern of multiple banding was also demonstrated in the adult and neonatal dog. However, rat and rabbit diaphragms had only a single, continuous end-plate band. Histochemical studies of fiber types in different parts of the feline diaphragm showed that costal, crural, and sternal subregions had similar overall proportions of fiber types. However, type SO (slow oxidative) fibers were distributed more densely on the thoracic than the abdominal surface of costal and crural, but not sternal subregions. Type SO fibers were also concentrated in fiber fascicles bordering the esophageal hiatus.