A sacromere is a segment between two adjacent Z discs and are essential for the striated structure of the cardiac and skeletal muscles.
Step-by-step explanation:
The Z disc is surrounded by the I band made of thin filament called actin. The I band is followed by the A band made up of thick filament called myosin. When the muscles contract the actin and the myosin become superimposed/overlapped.
The sliding filament model explains the contraction of the sacromere in which the Z discs move closer due to the overlapping of the thin and thick filaments. Thus the I band moves close to the A band which remain the same length as shown in figure.