LPT 321: Meat Science (1+1)

Z LINE ULTRA STRUCTURE

• In longitudinal section, an actin filament on one side of the Z line lies between two actin filaments on the opposite side of the Z line. This arrangement indicates that the actin filaments per se do not pass through the Z line.
• The actin filaments are believed to terminate at the Z line. Ultra-thin filaments, called Z filaments, constitute the material of the Z line and they connect with actin filaments on either side of it.
• Near the Z line, each actin filament connects to four Z filaments that pass obliquely through the Z line.
• Each of the four Z filaments then connects with an actin filament in the adjacent sarcomere. This structural arrangement of the Z line shows each actin filament of one sarcomere oriented in the centre of four actin filaments from the next sarcomere.
• In longitudinal sections, this offset (or oblique) arrangement of the Z filaments results in the characteristic zigzag pattern of the Z line and explains why an actin filament on one side of the Z line appears to lie between two actin filaments of the apposing sarcomere.