Nerve fiber ( nerves (Herophilus, c335-280 BC) ) : An unmyelinated axon or a myelinated axon; literally accurate for the peripheral nervous system, but often applied (ambiguously) to the central nervous system as well. In the second century Galen (see translations by Duckworth, 1962, p. 254; Clarke, 1968, p. 124) recognized the fibrous nature of nerves (Herophilus, c335-280 BC). Leeuwenhoek (1718; see Van der Loos, 1967, pp. 10-16) identified the nerve fiber itself as the ultimate structure of nerves and called it a vessel, whereas Ehrenberg (1833, pp. 453-456) called it a nerve fiber.

Nerves ( n ; Herophilus, c335-280 BC ) : A nerve is a topographic division with macroscopically recognizable bundles of axons (Kölliker, 1896), or white matter tracts, in the peripheral nervous system (Meckel, 1817) of invertebrates and vertebrates. A nerve can have a number of structural differentiations like roots, trunk, and branches, and can have a peripheral ganglion associated with it. When a series of ganglia is associated with a white matter tract, it is referred to as a peripheral nerve cord in the peripheral nervous system (Meckel, 1817), a central nerve cord in the central nervous system (Meckel, 1817) of invertebrates, or a radial nerve cord in a nerve net of invertebrates. Herophilus (c335-c280 BC), the founder of human anatomy, is credited with discovering nerves, including most of the cranial nerves (Longet, 1842) and spinal nerves (Camper, 1760) by distinguishing them from arteries; see Solmsen (1961, p. 185), von Staden (1989, pp. 250-252), and Longrigg (1993, pp. 192, 211).