Difference between Primary and Secondary Myofilaments – Comparison Table

primary vs secondary myofilaments

Primary Myofilaments vs Secondary Myofilaments
(Difference between the Primary Myofilaments and Secondary Myofilaments of Myofibrils)

Myofilaments are the filaments of myofibrils (myofibrils are the basic structural unit of muscle cells). The myofilaments are composed of proteins particularly actin and myosin. The detailed structural analysis shows that the muscle sarcomere composed of bundles of two types of myofilaments called primary myofilaments and secondary myofilaments. The present post discusses the difference between the Primary Myofilaments and Secondary Myofilaments with a comparison table.

Learn more: Difference between A-Band and I-Band

Difference between Primary and Secondary Myofilaments

Sl. No.Primary MyofilamentsSecondary Myofilaments
1Primary myofilaments are confined only to the A-band of a sarcomere.Secondary myofilaments occur in the I-band of the two adjacent sarcomeres.
2Primary myofilaments do not extend to the I-band.Secondary myofilaments are extended to some distance to the A-band
3Primary myofilaments are thicker and shorter than secondary myofilaments.Secondary myofilaments are thinner and loner than primary myofilaments.
4Primary myofilaments are free at both the ends.Secondary myofilaments are free at one end and the other end is joined to the Z line.
5Primary myofilaments consist of two proteins called Myosin and Meromyosin.Secondary myofilaments composed of three proteins called actin, tropomyosin and troponin.
6The occurrence of primary myofilaments is fewer than the secondary myofilaments.Secondary myofilaments are more numerous than primary myofilaments.
7Primary myofilaments do not slide during muscle contraction.Secondary myofilaments slide into the H-zone during muscle contraction.

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