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A Handbook of Biology

STRÜÇTÜRË ØF STRÏÅTËD MÜSÇLË

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Skeletal muscle is made of muscle bundles (fascicles) held together by

collagenous connective tissue layer (fascia).

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Each fascicle contains many muscle fibres (muscle cells).

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Muscle fibres are lined by plasma membrane (sarcolemma) enclosing

the sarcoplasm.

Sarcomere

Lighter I band

Lighter I band

Darker A band

Z line

Z line

H Zone

M line

Each muscle fibre contains myofilaments (myofibrils).

Each myofibril has alternate dark (Anisotropic or A- band) and light

striations (Isotropic or I-band). This is due to the presence of 2 fibrous

contractile proteins, thin actin filament and thick myosin filament.

I-bands contain actin. A-bands contain myosin. They are arranged

parallel to each other.

A-band bears a lighter middle region (H-band) formed of only

myosin. A thin dark line (M-line) runs through the centre of H-zone.

(NEET 2013)

I- band is bisected by a dense dark band called Z-line. Region

between two Z- line is called sarcomere, a structural and functional

unit of muscle.

(AIPMT 2001)

STRÜÇTÜRË ØF ÇØÑTRÅÇTÏLË PRØTËÏÑS

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An actin filament is made of 2 filamentous (F) actins which form

double helix.

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F-actin is a polymer of monomeric globular (G) actins.