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Anatomy Atlases: Atlas of Microscopic Anatomy: Section 1 - Cells Atlas of Microscopic Anatomy: Section 6 - Nervous Tissue

Plate 6.114 Spinal Root Nerve Fibers

Ronald A. Bergman, Ph.D., Adel K. Afifi, M.D., Paul M. Heidger, Jr., Ph.D.
Peer Review Status: Externally Peer Reviewed

A. Dorsal root B. Ventral root

Plate 6.114 Spinal Root Nerve Fibers

Rhesus monkey, 10% formalin, H. & E., 612 x.


The method used here demonstrates axons but not myelin, hence the clear areas around the centrally placed axons represent unstained myelin. The partitions in the clear areas are artifacts of fixation.

Note that nerve fibers in the ventral root (B) are, on the whole, larger than those in the dorsal root (A). Note also the variation in fiber size within both the dorsal and ventral roots. Very small fibers seen in B are unmyelinated. The capillary seen in B shows a crescent-shaped dark endothelial cell nucleus and clear lumen (perfusion fixation). A large, dark, crescent-like Schwann cell nucleus is also seen in B. Schwann cells elaborate the myelin sheath. The dorsal roots are composed of the central processes of unipolar neurons in the dorsal root ganglion (see Plates 100, 101, 102 and 103). The ventral roots are composed mainly of axons of the large somatic motoneurons, the smaller gamma motoneurons, and visceromotor axons from the autonomic intermediolateral cell column.

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