Muscle Histology
The technique of muscle biopsy is not difficult. Under local anesthesia, a small incision made over the muscle allows, with careful dissection, removal of a small strip of muscle. Needle biopsies are useful in some situations. Histochemical studies of frozen sections are essential for proper interpretation. A transverse section of normal muscle shows fibers that are roughly of equal size and average approximately 60 mm in transverse diameter ( Fig. 110.1 ). The muscle fibers of infants and young children are proportionately smaller. Each fiber consists of hundreds of myofibrils separated by an intermyofibrillar network containing aqueous sarcoplasm, mitochondria, and the sarcoplasmic reticulum with the associated transverse tubular system. Surrounding each muscle fiber is a thin layer of connective tissue (the endomysium). Strands of connective tissue group fibers into a fascicle, separated from each other by the perimysium. Groups of fascicles are collected into muscle bellies surrounded by epimysium.