Neurons with Somata Outside the Spinal Cord Sending Axons to the Cord

  • Santiago Ramón y Cajal


The dorsal or sensory roots of the spinal cord represent the central processes of unipolar cells in the spinal ganglia; therefore, every sensory root, being spinal or cranial, depends on a ganglion where it has its trophic center, and from which it will receive the nerve impulse. These ganglia are intercalated in the bulk of the dorsal root before its junction with the ventral root.


Methylene Blue Ganglion Cell Satellite Cell Trigeminal Ganglion Spinal Ganglion 
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  1. 1.
    It is also possible that the bundle of initial fibers described by Hans Daae (1888) in the spinal ganglia of mammals, was wrongly observed and interpreted as fusing in a single fiber. It represents, in fact, the initial glomerulus.Google Scholar
  2. 2.
    Apparently, also Huber (1896) stained these arborizations in the frog.Google Scholar
  3. 3.
    In this article, Flemming advocates for his gradual staining method with weak solutions of Delafield hematoxylin. Rawitz (1895) also advises the use of slow staining procedures using his formula of glycerinated hematein.Google Scholar
  4. 4.
    We have seen recently in ganglia of the frog and toad, stained with hematoxylin, some bipolar cells with the two appendages originating on the same side of the cell. Morphologically, such cells represent a transition between the bipolar and unipolar types.Google Scholar
  5. 5.
    We have observed first the spiral figures in an excellent preparation of Levi, belonging to ganglia of Bufo (sacrificed after hibernation), which we owe to the exquisite kindness of Lugaro. But later, we confirmed their presence also in frogs, which had been in the laboratory for a long time, as well as in the toad and sand lizard.Google Scholar


  1. a.
    Cajal uses the term neurilemma instead of epineurium. See annotation f in Chapter IX.Google Scholar
  2. b.
    Fig. 151.—A, B, the two neurons; a, glomerular indentation; b, increased number of nuclei; c, pericellular capsule; d, nuclei of capsule.Google Scholar
  3. c.
    Fig. 153.—c, axon with simple loop.Google Scholar
  4. d.
    Fig. 154.—G, small cell with rudimentary glomerulus; a, diffuse glomerulus; b, first myelin segment starting close to the exit from the capsule; e, long unmyelinated segment after exiting from the capsule.Google Scholar
  5. e.
    Fig. 155.—a, glomerular indentation; b, start of myelin sheath.Google Scholar
  6. f.
    Fig. 160.—b, axon; a, terminal knob.Google Scholar
  7. g.
    Fig. 162.—d, filiform dendritic process terminating in a knob.Google Scholar
  8. h.
    Fig. 164.—a, e, filiform processes joining a dendrite and the soma; b, axon with club-shaped ending process; c, filiform process joining the axon with the soma; d, axon; f, filiform process joining two sites of the axon.Google Scholar
  9. i.
    Fig. 166.—R, endothelial cells surrounding the ganglion; a, central process of unipolar neuron; b, d, peripheral processes of unipolar neurons; e, f, postganglionic sympathetic axons joining the spinal nerve; g, preganglionic sympathetic axon; j, same as p, i, h, i.e. sympathetic fibers entering the ganglion.Google Scholar
  10. j.
    Fig. 168.—b, varicose free ending of the pericellular arborization; d, turns of the pericellular arborization.Google Scholar
  11. k.
    It is well known today that initial portions of some axons receive synaptic contacts of boutons derived from other axons in an axoaxonic pattern of Connectivity. A clear example are the synapses made by axon terminals of chandelier cells and initial segments of pyramidal cells axons in the cerebral cortex [Szentágothai (1975) Brain Res 95: 475-496]. Following the law of dynamic polarization, Cajal was forced to consider that the initial unmyeli-nated portion of the sensory cell process was of dendritic nature, and became axonic only after the last contact with other axon terminals.Google Scholar
  12. l.
    Fig. 170.—b, glomerulus; d, afferent fibers; e, capsule.Google Scholar
  13. m.
    See annotation d in Chapter IV regarding pericellular arborizations in sensory ganglia.Google Scholar
  14. n.
    Cajal uses here the term adventitious cells instead of satellite cells.Google Scholar

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© Springer-Verlag Wien 1999

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  • Santiago Ramón y Cajal

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