Definition of the Terms About the Peripheral Nervous System

The peripheral nerve connects the CNS with receptors on the periphery and executive organs and can contain myelinated or unmyelinated fibres along with the connective tissue in the form of the endoneurium, mesoneurium, perineurium, and epineurias for isolation of different nerve parts. Clinical symptoms of peripheral nerve damage include movement or sensitivity disorders and vascular or motor disorders of nerve functions. The injury itself should be complicated with adjacent structure damage and thus complicate the exact diagnosis along with the presence of various nervous interconnections. Causalgia is the manifestation of nerve irritation and occurs when a nerve is even partially damaged. It can be associated with irritation of its sympathetic fibres resulting in vasomotor, secretory, and trophic disorders. The variability of nerve injury clinical symptoms in different people is due to the different number of contents of myelinated and unmyelinated fibres within it. The largest number of autonomic fibres was observed in the median nerve and tibial nerves. Atypical symptoms can be also explained by the presence of anastomoses of the damaged nerve with surrounding ones. Many such variations are present in the formation of the cervical, brachial, and lumbosacral plexus and are sources of atypical clinical and electromyographic findings and diagnostic confusion. Our work aims to point out the anatomical variations of PNS and their participation in the clinic, as there are only rare sources devoted to this topic in the literature.