Z linen.

1916 Jordan & Ferguson Text-bk. Histol. iv. 105 This stripe or accessory disk..bisects the portion of the J disk between the Z line and the succeeding Q disk.

1954 Nature 22 May 976/1 The series elastic component is provided either by the actin filaments themselves, or, more probably, by their mode of attachment to the Z-line.

1979 Sci. Amer. May 94/2 In muscle fibers the actin filaments are anchored to flat protein structures called Z lines, which are emplaced between every two contractile units.

1950 A. W. Ham Histol. xix. 283/1 When a substantial degree of contraction has occurred, an appearance, often referred to as a ‘reversal of striations’, becomes apparent. This is due to the substance of the myofibril on each side of the Z band, which was formerly light, becoming dark, and the dark material of the Q band becoming light.

1964 G. H. Haggis et al. Introd. Molecular Biol. iv. 101 The segment from one Z-band to the next, along a fibril, is termed a sarcomere.

1970 Fallis & Ashworth Textbk. Human Histol. viii. 58 The major cross bands of the myofibrils are the A and I bands... In the center of the I band is a thin dark line known as the Z (Zwischenscheibe) band, or intermediate line of Krause; the Z band attaches to the sarcolemma at the periphery of the cell.