Page 382 - Atlas of Histology with Functional Correlations

FIGURE 9.27 ■ Peripheral nerve: nodes of Ranvier and axons. Stain: Masson
trichrome. ×100.

FIGURE 9.28 | Ultrastructure of Peripheral Nerve

Fascicle in PNS Cut in Transverse Plane

A transmission electron micrograph of a nerve fascicle sectioned in a transverse
plane shows two large myelinated axons (3) on the left side and small

unmyelinated axons (7) on the right side. In contrast to the CNS, the Schwann
cells only form myelin sheaths (2) around a section of one axon. A thin rim of
Schwann cell cytoplasm (5) surrounds the myelinated axon, which is invested
by an outer thin layer of basal lamina (6). Within the axons are oval-shaped,

dense-staining mitochondria (4). On the right side are Schwann cells that
surround numerous unmyelinated axons (7) that are embedded in the Schwann
cell cytoplasm (8). A thin basal lamina (10) also surrounds the Schwann cell
cytoplasm (8) that encloses the unmyelinated axons (7). Similar oval-shaped

mitochondria (9) and neurofilaments are found in the unmyelinated axons (7).
Enclosing the nerve fascicle is a thin layer of connective tissue perineurium
(12). On the peripheries of the fascicle are cells with developed rough
endoplasmic reticulum that are most likely the fibroblasts (1, 11).

A transmission electron micrograph of Figure 9.19 illustrates the node of
Ranvier from the CNS. Except for a few ultrastructural differences, the
structures of the nodes of Ranvier in the PNS and the CNS are similar. The
nodes in the PNS are covered by the basal lamina, whereas the nodes in the
CNS lack an overlying basal lamina.

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