Muscle biopsy showing ringed fibres

Transmission electron micrograph of a muscle biopsy showing a ring fibre with myofibrils running around the periphery of the muscle, perpendicular to the majority of the myofibrils. This can cause muscle weakness and is typical of pathological changes seen in myotonic dystrophy. These ring fibres show the typical sarcomeric unit of thick and thin fibres, Z lines and M lines, A bands and I bands. Endomysium cells are visible between the muscle cells.