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. Author manuscript; available in PMC: 2018 Apr 9.
Published in final edited form as: Compr Physiol. 2017 Jun 18;7(3):891–944. doi: 10.1002/cphy.c160033

Figure 1.

Figure 1

(A) Schematic representation of a cardiac sarcomere (lacking nebulin) illustrating the three major filament systems: actin-based thin filaments (gray), myosin-based thick filaments (blue), and titin (pink). The lateral boundaries of the sarcomere are the Z-discs. The I-bands surrounds the Z-disc and is a region where thin filaments are not superimposed by thick filaments. The A-band region contains thin filaments and thick filaments. The M-band falls within the H-zone, where thick filaments do not interdigitate with thick filaments. (B) Electron micrograph of skeletal muscle sarcomere. (C) Enlarged view of the M-band region. The M-band is composed of a series of three to five electron-dense M-lines: M6′, M4′, M1, M4, and M6. [Part A modified, with permission, from (255); Parts B and C modified, with permission, from (9).]