4.6K views · 72 reactions | This is how your muscles look from the inside: This is a 3D video of muscle cells' nuclei and the mitochondrial matrix in a human muscle fiber. In order to see these structures, a DAPI staining is needed. DAPI is a fluorescent stain that binds strongly to A-T rich regions in DNA. As DAPI can pass through an intact cell membrane, it can be used to stain both live and fixed cells. | EM-SportScience | Facebook

1. A muscle's contractile units lie within individual muscle cells, which are also called muscle fibers. Each muscle fiber contains numerous bundles of protein filaments. These bundles, called myofibrils, are organized into repeating contractile units called sarcomeres. 2. A sarcomere contains two types of protein filaments: actin filaments and myosin filaments. Each actin filament is attached to a Z line, which is found at either end of a sarcomere. The thick myosin filaments lie between the Z