Page 74 - Headlines Histology2024_Neat

• From the epimysium, thin collagenous septa extend inward to divide the
muscle into a number of bundles or fascicles. These septa are called the
perimysium.

• The perimysium is continuous with the endomysium that is a delicate
connective tissue layer surrounds each individual myofibers.

• At least five cell types are found within the bundle of the skeletal muscle:
myofibers, endothelial cells, fibroblasts and myosatellite cells.

• The connective tissue in between the myofibers is needed for two reasons:
1) through which blood vessels, lymphatics and nerve enter or leave the
interior of the muscle. 2) At the ends of the muscle, the connective tissue
elements merge to form tendons that anchor the muscle to other structures
such as bone or cartilage.

Structure of skeletal myofiber

• At the LM level, the skeletal myofibers are extremely long, multinucleated
cylindrical cells. Their diameter range from 10-100 ?m and their length
about 1-4 mm.

• The nuclei are oval, elongated and are located just underneath the
sarcolemma.

• In longitudinal sections, the sarcoplasm is acidophilic and crosses striated
with alternating dark and light-staining transverse bands.

• Under the polarized light, the dark-staining bands are called anisotropic or
A-bands because polarized light is reflected unequally when passed through
it.

• The light-staining bands are called isotropic or I-band because polarized
light is reflected equally when passed through it. Dark lines termed Z-lines
or Z-disc bisects the I-bands. The center of each A-band contains a paler
region called H-zones or H-band.

• The distance between two successive Z lines is called sarcomere that is the
contractile unit of the skeletal muscles.

74