Myofibrils are parallelly organised within each muscle fibre.
The functional units, known as sarcomere, are serially arranged within each myofibril.
Each sarcomere consists of a core "A" band made of thick myosin filaments and two half "I" bands on either side of it that are made of thin actin filaments and identified by "Z" lines.
At rest, the thick filaments' free ends partially overlap the edges of the thin filaments on each side of them, leaving the thick filaments' centre intact.
The "H" zone refers to the centre of the thick filament that is not covered by any thin filaments.