Structural features of connections between corticospinal fibers and neurons of the cervical and lumbar segments of the cat spinal cord were studied by the experimental degeneration method. It was shown by the Fink-Heimer method that the preterminals of these fibers are mainly located in the lateral part of Rexed's laminae V and VI (the lateral basilar region — LBR) and also, to some extent, in the medial basilar region (MBR). The diameters of the myelinated part of these fibers in LBR vary from 0.8 to 11µ. They form chiefly terminals of the F-type (with flattened synaptic vesicles), which undergo degeneration of the “light” type (lysis of the internal structures) or, less frequently, the “dark” type (increase in electron density), followed by phagocytosis by glial cells. No degenerating terminals are found in the glomerulus-like synaptic complexes, in axo-axonal synapses, or on dendrites with a “dark” matrix. Only a few degenerating axon terminals still remained 20 days or more after extirpation of the cortex. The relative number of terminals of different types was counted at this period. The number of axon terminals of F-type on the dendrites was reduced by 1.5 times, while the number on the soma remained relatively unchanged. The results confirm the earlier hypothesis that corticospinal fibers terminate on dendrites and their appendages in LBR as endings of the F-type. These neurons also receive many terminals from other intracerebral systems.
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Kostyuk, P.G., Pogorelaya, N.K. & D'yachkova, L.N. Structural features of corticospinal connections in the cat. Neurophysiology 4, 367–376 (1972). https://doi.org/10.1007/BF01063007
- Spinal Cord
- Structural Feature
- Glial Cell
- Lateral Part
- Synaptic Vesicle