Components of the Nervous Tissue
As discussed previously, all neural organs, whatever their complexity, result from the interweaving of three elements: the nerve cell, the axon or conducting fiber which is just a continuation of the cell, and the neuroglial cell.
KeywordsNerve Cell Sensory Cell Amacrine Cell Spiral Ganglion Spinal Ganglion
Unable to display preview. Download preview PDF.
- 1.Of all the designations given to the nerve cell and its processes, we will use preferentially the word neuron (Waldeyer) to name the whole cell, axon (Kölliker) for the functional process, dendritic or protoplasmic appendages for the non-axonal processes, and soma for the cell body.Google Scholar
- 2.The idea of grouping all types of sensory cells into a single special group of neurons characterized by the duality of processes and their perfect polarization, was offered originally by us (Cajal, 1889b). In order to fit the unipolar cell of the spinal ganglia, which is the ontogenetic and phylogenetic homologue of the bipolar olfactory and acoustic elements, into the same category, we assumed that its peripheral expansion was of dendritic nature. This generalization was not only accepted but amplified by Retzius (1890a; 1892i, k; 1895a) who extended it to the invertebrates, and demonstrated that the differences between the various sensory cells are entirely topographical. Lenhossék, with his elegant discovery of sensory cells in worms, and Van Gehuchten’s ideas on the dynamics of dendrites, strengthened the foundations of what appeared at first glance to be a very daring doctrine. We should recall in this historical note, the valuable contribution of His (1889) who, with his important investigations on the histogenesis of ganglia, confirmed later by us, Lachi, Lenhossék, Van Gehuchten, Retzius, and others, prepared the ground for such a theory. He demonstrated, among other issues, the original bipolarity of unipolar cells in spinal ganglia, teaching us that every sensory root represents the central process of extramedullary ganglion cells entering the spinal cord or the medulla.Google Scholar
- 3.To designate these cells, we shall use indistinctly the terms Golgi cells (in honor of their discoverer) or short axon cells which has the advantage of translating faithfully the axonal pattern with no physiologic biases.Google Scholar
- a.Textura reads in error dorsal instead of cervical.Google Scholar
- b.Cajal uses here the old designation of spongioblasts for what he later named as amacrine cells.Google Scholar
- c.It is now well known that processes of amacrine retinal cells may be presynaptic as well as postsynaptic and therefore exhibit characteristics of both axons and dendrites [Dowling, Boycott (1996) Proc Roy Soc London B, 166: 80-111]. This is one example of an apparent challenge to the law of dynamic polarization discussed in our preface.Google Scholar
- d.Cajal eventually changed his view on the amacrine nature of the special cells in the molecular layer of the cerebral cortex. In Volume III, Chapter XXXII, on describing the horizontal cells of this layer, he recognizes the axonal character of just one of the processes.Google Scholar
- e.Fig. 6.—A, B, unipolar cell bodies; a, b, emergence of collateral or more probably bifurcation of the single stem.Google Scholar
- f.Cajal uses the term descending motor root for the mesencephalic root of the trigeminal nerve. The cells providing these fibers are known to be first order sensory neurons similar to those residing in dorsal root and cranial nerve sensory ganglia, and represent the afferent limb of the mandibular or jaw-closure reflex [Szentágothai (1948) J Neurophysiol 11: 445-454].Google Scholar
- g.Cajal reversed the Golgi types, naming the long and short axon cells as the second and first type respectively. It has been corrected in the present text.Google Scholar
- h.Fig. 10.—C, axon; r, part of axon terminal arborization.Google Scholar
- i.It is now known that the prevailing neuronal type in the striatum, to which Cajal refers here as the corpus striatum, is a Golgi type I or long axon cell [Pasik, Pasik, DiFiglia (1979) in: Divac, Oberg (eds) The Neostriatum. Pergamon, Oxford, pp 5-36]. See full discussion in corresponding annotation in Volume III.Google Scholar