Normal Skeletal Muscle

Epidemiology and Etiology:

Common sites:

Gross features:

Histologic features:

· 1 nucleus in 3-5% of muscle fibres may be interior rather than peripheral

· muscle fibres are polygonal in adults

o round in kids, and in extrinsic eye muscles and some facial muscles of adults

o

Immunophenotype:

Marker:

Sensitivity:

Specificity:

· normally a checkerboard pattern of Type 1 and Type 2 fibres

o different muscle groups may have different proportions

· Type 1

o dark staining for ATPase at pH 4.2, light staining at pH 9.4

o NADH dark staining

· Type 2

o light staining for ATPase at pH 4.2, dark staining at pH 9.4

o NADH light staining

Molecular features:

Other features:

· Type 1 fibres:

o “One slow fat red ox”

§ Type 1 fibres

§ Slow twitch

§ Lipid-rich

§ Red appearance

§ Oxidative

o Sustained force

o Weight-bearing

o Scant glycogen (high lipid)

o EM:

§ many mitochondria

§ Wide Z-band

· Type 2 fibres:

o

o EM:

§ few mitochondria

§ Wide Z-band

o

References: