The CRANIAL and spinal nerve roots as they emerge from the central nervous system (CNS) do not immediately assume the architecture of a peripheral nerve. Their morphological structure first resembles that of a fiber bundle within the brain or spinal chord with abundant neuroglial supporting elements: astrocytes, oligodendrocytes, and microglia.1 This proximal neuroglial portion of the nerve root ends with the penetration of the nerve through the pia. Upon penetrating the pia the neuroglia is abandoned. The individual nerve fibers pass through a lamina cribrosa composed of reticulin, beyond which each fiber is contained within its ensheathing tube of reticulin and Schwann cell elements. Schwann cells sheath the axons from here to their ends.The distance from the neuraxis at which the nerve penetrates the pia varies from root to root. A sensory-nerve root generally has a longer neuroglial portion than a motor-nerve root. In the facial
Nager GT. Acoustic Neurinomas: Pathology and Differential Diagnosis. Arch Otolaryngol. 1969;89(2):252–279. doi:10.1001/archotol.1969.00770020254008
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