Abstract
The spinal gray matter is a complex structure with the following components: 1st., numerous nerve cells of long axon; 2nd., very few cells of short axon; 3rd., free ramifications of collaterals from white matter; 4th., free terminal arborizations of white matter fibers; 5th., initial collaterals, i.e. those emerging from axons of neurons during their course through the gray matter; 6th., neuroglial cells; 7th., ependymal cells; and 8th., capillaries.
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Footnotes
Our repeated attempts to stain these cells in the adult cat, rabbit and pigeon with the Ehrlich method (intravascular injection of methylene blue), or that of Dogiel (direct immersion in the methylene blue solution), have resulted in good staining of only the axons.
We do not know whether this author has published this finding; but in any event we wish to record that in 1887 he showed us several preparations stained with hematoxylin which exhibited the spiral masses very clearly.
Also Valenza (1897a) has described recently a spiroidal arrangement in many myelinated fibers of the human embryo stained with the Weigert-Pal method. We believe with Valenza that these spiroidal courses are due to mechanical factors (excessive growth of the axon within the surrounding sheath), which disappear at maturity.
The ideas of Schaffer (1897a), as published in his article, do not consider any of the findings of pericellular or peridendritic connections discovered in the last years. It is not worth it therefore to belabor in refuting such a capricious opinion. (See also Cajal, 1897c, p 38)
The letter addressed to Lenhossek included some preparations, in one of which appeared with absolute clarity a large dorsal root fiber that crossed entirely the immediate spinal ganglion without bifurcating in the dorsal funiculus or connecting to any sensory element.
Annotations
Textura reads never instead of rarely as in the Histologie. b Fig. 127.—E, ventral horn of the opposite side
It is currently accepted that most fibers of the pyramidal tract do not contact directly motoneurons. Instead, they enter into networks made by other nerve cells of the ventral horn, and only the output of these networks carried by short axons influence motoneurons [Szentagothai-Schimert (1941) Ztschr Anat Entwickl Gesch 111: 322-330].
Fig. 129.—A, Textura reads in error lateral motor nucleus instead of ventral root.
Although the emergence of collaterals within 30 çm of the axon origin may be the case for motoneurons, it is not a general rule for the entire nervous system. For example the axon of spiny neurons of the monkey neostriastum emits collaterals up to 200 çm from the soma [DiFiglia, Pasik, Pasik (1976) Brain Res 114: 245-256]
It is worth noting that the Renshaw cell recurrent inhibition concept, by which recurrent collaterals of motor axons participate in controlling the output of the parent cell through the activation of inhibitory interneurons which in turn inhibit the motoneuron, has been substantiated morphologically [Szenta-gothai (1958) Acta Morph Acad Sci Hung 8: 287-309].
The existence of an occasional sensory cell embedded in a ventral root is now an accepted fact. For review see: Willis, Coggeshall (1978) Sensory mechanisms of the spinal cord. Plenum, New York London, pp 47-48.
Fig. 130.—D, E, F, commissural cells of the dorsal horn; G, growth cones of ventral funiculus collaterals.
Cajal attributes an endothelial nature to the sheath of Henle, which is in fact made of reticulin fibers. See annotationd in Chapter IX.
Textura and Histologie omit mentioning the equivalents of Fig. 131 in the texts.
That the motor fiber terminates within a muscle cell is indeed a strange statement coming from Cajal. In any event, the morphology of the neuromuscular junction is clearly that of a synapse with the presynaptic and postsynaptic membranes belonging to the axon terminal and muscle cell, respectively [Robertson (1956) J Biophys Biochem Cytol 2: 381-395].
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y Cajal, S.R. (1999). Structure of the Gray Matter. In: Texture of the Nervous System of Man and the Vertebrates. Springer, Vienna. https://doi.org/10.1007/978-3-7091-6435-8_12
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DOI: https://doi.org/10.1007/978-3-7091-6435-8_12
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