Fiber spectrum of the trigeminal sensory root of the baboon determined by electron microscopy

✓ Using random sampling methods and the electron microscope we have verified the impression gained from light microscopy that unmyelinated fibers compose only about 40% of the total fiber count of the trigeminal root. By contrast, recent electron microscopic studies of segmental dorsal roots indicate that, at least in lower vertebrates, unmyelinated fibers compose up to 80% or more of the total. This observation is considered to be of descriptive rather than physiological or pathological significance. The morphological alterations that occur in the spinal trigeminal tract appear to restore the balance in favor of unmyelinated fibers at the functional termination of the trigeminal sensory root.