On histology, the 'Z line' in a skeletal muscle sarcomere represents attachment of which protein, and its absence in a neonate with nemaline myopathy would be associated with defects in which structural component?

• A Titin (connectin); thick filament (myosin) attachment
• B Myosin-binding protein C; thick filament regulation
• C Desmin; connecting Z discs of adjacent myofibrils
• D Alpha-actinin; thin filament (actin) anchoring to the Z disc ✓

Explanation

The Z line (Zwischenscheibe = 'between disc') is an electron-dense band at either end of the sarcomere where thin filaments (actin) are anchored via alpha-actinin. Nemaline rods in nemaline myopathy are abnormal accumulations of Z-disc material (primarily alpha-actinin, actin, and related proteins) within the sarcoplasm — they appear as rod-shaped structures on modified Gomori trichrome stain. Titin spans from Z disc to M band; desmin is an intermediate filament connecting Z discs between adjacent myofibrils (not within the Z disc itself).

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.