Development of Nerve Connections with Muscles and Peripheral Sense Organs

Abstract

We have considered the growth of knowledge about out growth of nerve fibers (Section 5.1) and note here only the historical origins and early evolution of ideas about peripheral nerve endings. The history of ideas about the modes of termination of peripheral nerve fibers parallels that of ideas about endings of nerve fibers in the central nervous system (CNS). Until the 1860s it was generally believed that the peripheral nerves end by anastomosing with one another to form plexuses in the skin and muscles. It was also thought that sensoI) nerve fibers branch and anastomose in the skin and mucous membranes and then recombine to form ijbers that return to the CNS (Beale, 1860, 1862). The concept of anastomosis between the processes of nerve cells in the CNS was supported by the evidence available at that time (see Sections 5.1 and 6.1). Both central and peripheral nervous systems were believed to be organized on the principle of nerve networks. Microscopes could not resolve individual fine unmyelinated nerve fibers in the peripheral nerves. They revealed fascicles which were mistaken for single nerve fibers. Interlacing of such fascicles was misconstrued as true anastomoses between fibers. As we shall see later , this misconception persisted until Ranson (1911) showed that peripheral nerves contain large numbers of unmyelinated fibers and proved that they are sensoI) (Ranson, 1913, 1914, 1915).

If anyone offers conjectures about the troth of things from the mere possibility of hypothesis, then I do not see how any certainty canbe determinedin any science;for it is always possible to contrive hypotheses, one after another, which arefound to lead to new difficulties.

Isaac Newton, “Letter to Pardies, 10 June 1672” (In The Correspondence of Isaac Newton, H. W. Turnbull, ed., Cambridge University Press, Cambridge, 1959)

John F. Fulton (1899–1960), Physiology of the Nervous System, 1st ed., p. 40, 1938

The quest of a single neuromuscular unit has in fact had many of the dramatic features associated with the quest for a single atom, and the success achieved by the physiologist is in most respects quite as remarkable as that of the physicist.

John F. Fulton (1899–1960), Physiology of the Nervous System, 1st ed., p. 40, 1938