Primary injury to the cell body (neuronopathy) can result in destruction of the neuron cell body and irreparable secondary loss of its axon and associated degeneration of the entire myelin sheath. Primary damage to the axon (axonopathy) leads to loss of the distal axon and secondary disintegration of its myelin sheath sometimes with swelling and chromatolysis of the neuronal cell body (i.e., the “axonal reaction”) to support axon regrowth. Compared to the normal condition (left), injury (shown by arrows) leads to different patterns of toxicant-induced injury to myelinated peripheral nerve fibers depending on the target. An example of a normal ganglion, in this case a dorsal root (or spinal) ganglion, is provided in Figure 4.įigure 5. Multiple unmyelinated fibers are enfolded by the cytoplasm of a single Schwann cell ( Figure 2). In myelinated fibers, individual Schwann cells form the internodal segments of myelin, with each cell separated from its neighbors at the nodes of Ranvier ( Figures 1 and 2).
Somatic nervous system drawing series#
Within this protected endoneurial space lie fascicles of myelinated and unmyelinated nerve fibers each encompassed by a sheath formed by a linear series of Schwann cells. The latter is a multilayered structure with tight junctions between cells, forming a diffusion barrier isolating the interior (endoneurium) of the fascicles. The organization of a prototypical peripheral nerve as seen in cross section is demonstrated in Figure 2 (as a diagram) and Figure 3 (as a photomicrograph), which show its components including the connective tissue sheaths, the outer epineurium, and the specialized perineurial barrier. As noted above, this review article is focused on the somatic myelinated components of the PNS, including peripheral motor and sensory fibers, along with neuronal cell bodies that reside in ganglia. This diagram demonstrates both the somatic and autonomic elements ( Schaumburg, Berger, and Thomas 1983).
Organization and Components of the PNSĪ summary of the components and organization of the PNS is demonstrated in Figure 1. Some aspects of the present article are drawn from a previously published work ( Jortner 2011).
To reflect contemporary practice of peripheral nerve pathology ( Schröder 2001), most of the light microscopic material presented in this review is from toluidine blue–stained, semithin sections of aldehyde-fixed, osmium tetroxide postfixed, epoxy resin–embedded nerve samples. Next, are examples of classic experimentally induced lesions of peripheral nerve myelinated fibers representing three classic categories of toxic neuropathy: neuronopathy, axonopathy, and demyelination. First is a brief review of the organization and histologic features of the PNS. There are several components to this article. This review article is derived from a talk on common toxicant-induced structural lesions of peripheral nerves that was given at a ½-day continuing education course on toxicologic pathology of the peripheral nervous system (PNS) that was presented at the 37th annual meeting of the Society of Toxicologic Pathologists, June 2018 ( Pardo et al. All subjects Allied Health Cardiology & Cardiovascular Medicine Dentistry Emergency Medicine & Critical Care Endocrinology & Metabolism Environmental Science General Medicine Geriatrics Infectious Diseases Medico-legal Neurology Nursing Nutrition Obstetrics & Gynecology Oncology Orthopaedics & Sports Medicine Otolaryngology Palliative Medicine & Chronic Care Pediatrics Pharmacology & Toxicology Psychiatry & Psychology Public Health Pulmonary & Respiratory Medicine Radiology Research Methods & Evaluation Rheumatology Surgery Tropical Medicine Veterinary Medicine Cell Biology Clinical Biochemistry Environmental Science Life Sciences Neuroscience Pharmacology & Toxicology Biomedical Engineering Engineering & Computing Environmental Engineering Materials Science Anthropology & Archaeology Communication & Media Studies Criminology & Criminal Justice Cultural Studies Economics & Development Education Environmental Studies Ethnic Studies Family Studies Gender Studies Geography Gerontology & Aging Group Studies History Information Science Interpersonal Violence Language & Linguistics Law Management & Organization Studies Marketing & Hospitality Music Peace Studies & Conflict Resolution Philosophy Politics & International Relations Psychoanalysis Psychology & Counseling Public Administration Regional Studies Religion Research Methods & Evaluation Science & Society Studies Social Work & Social Policy Sociology Special Education Urban Studies & Planning BROWSE JOURNALS
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