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. 1968 Dec 1;39(3):604–619. doi: 10.1083/jcb.39.3.604

THE SMALL PYRAMIDAL NEURON OF THE RAT CEREBRAL CORTEX

The Axon Hillock and Initial Segment

Alan Peters 1, Charmian C Proskauer 1, Ita R Kaiserman-Abramof 1
PMCID: PMC2107556  PMID: 5699934

Abstract

The axon of the pyramidal neuron in the cerebral cortex arises either directly from the perikaryon or as a branch from a basal dendrite. When it arises from the perikaryon, an axon hillock is present. The hillock is a region in which there is a transition between the cytological features of the perikaryon and those of the initial segment of the axon. Thus, in the hillock there is a diminution in the number of ribosomes and a beginning of the fasciculation of microtubules that characterize the initial segment. Not all of the microtubules entering the hillock from the perikaryon continue into the initial segment. Distally, the axon hillock ends where the dense undercoating of the plasma membrane of the initial segment commences. Dense material also appears in the extracellular space surrounding the initial segment. The initial segment of the pyramidal cell axon contains a cisternal organelle consisting of stacks of flattened cisternae alternating with plates of dense granular material. These cisternal organelles resemble the spine apparatuses that occur in the dendritic spines of this same neuron. Axo-axonal synapses are formed between the initial segment and surrounding axon terminals. The axon terminals contain clear synaptic vesicles and, at the synaptic junctions, both synaptic complexes and puncta adhaerentia are present.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. ELFVIN L. G. The ultrastructure of the nodes of Ranvier in cat sympathetic nerve fibers. J Ultrastruct Res. 1961 Aug;5:374–387. doi: 10.1016/s0022-5320(61)80014-2. [DOI] [PubMed] [Google Scholar]
  2. GRAY E. G. Axo-somatic and axo-dendritic synapses of the cerebral cortex: an electron microscope study. J Anat. 1959 Oct;93:420–433. [PMC free article] [PubMed] [Google Scholar]
  3. Gray E. G., Guillery R. W. Synaptic morphology in the normal and degenerating nervous system. Int Rev Cytol. 1966;19:111–182. doi: 10.1016/s0074-7696(08)60566-5. [DOI] [PubMed] [Google Scholar]
  4. HAMLYN L. H. The fine structure of the mossy fibre endings in the hippocampus of the rabbit. J Anat. 1962 Jan;96:112–120. [PMC free article] [PubMed] [Google Scholar]
  5. PALAY S. L., McGEE-RUSSELL S. M., GORDON S., Jr, GRILLO M. A. Fixation of neural tissues for electron microscopy by perfusion with solutions of osmium tetroxide. J Cell Biol. 1962 Feb;12:385–410. doi: 10.1083/jcb.12.2.385. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. PALAY S. L. Synapses in the central nervous system. J Biophys Biochem Cytol. 1956 Jul 25;2(4 Suppl):193–202. doi: 10.1083/jcb.2.4.193. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. PEASE D. C. THE ULTRASTRUCTURE OF FLAGELLAR FIBRILS. J Cell Biol. 1963 Aug;18:313–326. doi: 10.1083/jcb.18.2.313. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Palay S. L., Sotelo C., Peters A., Orkand P. M. The axon hillock and the initial segment. J Cell Biol. 1968 Jul;38(1):193–201. doi: 10.1083/jcb.38.1.193. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Peters A., Palay S. L. The morphology of laminae A and A1 of the dorsal nucleus of the lateral geniculate body of the cat. J Anat. 1966 Jul;100(Pt 3):451–486. [PMC free article] [PubMed] [Google Scholar]
  10. Peters A. The node of Ranvier in the central nervous system. Q J Exp Physiol Cogn Med Sci. 1966 Jul;51(3):229–236. doi: 10.1113/expphysiol.1966.sp001852. [DOI] [PubMed] [Google Scholar]
  11. Peters A., Vaughn J. E. Microtubules and filaments in the axons and astrocytes of early postnatal rat optic nerves. J Cell Biol. 1967 Jan;32(1):113–119. doi: 10.1083/jcb.32.1.113. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. RAMON-MOLINER E. The histology of the postcruciate gyrus in the cat. III. Further observations. J Comp Neurol. 1961 Oct;117:229–249. doi: 10.1002/cne.901170209. [DOI] [PubMed] [Google Scholar]
  13. ROBERTSON J. D., BODENHEIMER T. S., STAGE D. E. THE ULTRASTRUCTURE OF MAUTHNER CELL SYNAPSES AND NODES IN GOLDFISH BRAINS. J Cell Biol. 1963 Oct;19:159–199. doi: 10.1083/jcb.19.1.159. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. ROSENBLUTH J. Subsurface cisterns and their relationship to the neuronal plasma membrane. J Cell Biol. 1962 Jun;13:405–421. doi: 10.1083/jcb.13.3.405. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Reese T. S., Karnovsky M. J. Fine structural localization of a blood-brain barrier to exogenous peroxidase. J Cell Biol. 1967 Jul;34(1):207–217. doi: 10.1083/jcb.34.1.207. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Rodríguez Echandía E. L., Piezzi R. S., Rodríguez E. M. Dense-core microtubules in neurons and gliocytes of the toad Bufo arenarum Hensel. Am J Anat. 1968 Jan;122(1):157–166. doi: 10.1002/aja.1001220110. [DOI] [PubMed] [Google Scholar]
  17. Uchizono K. Characteristics of excitatory and inhibitory synapses in the central nervous system of the cat. Nature. 1965 Aug 7;207(997):642–643. doi: 10.1038/207642a0. [DOI] [PubMed] [Google Scholar]
  18. VENABLE J. H., COGGESHALL R. A SIMPLIFIED LEAD CITRATE STAIN FOR USE IN ELECTRON MICROSCOPY. J Cell Biol. 1965 May;25:407–408. doi: 10.1083/jcb.25.2.407. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Westrum L. E. Synaptic contacts on axons in the cerebral cortex. Nature. 1966 Jun 18;210(5042):1289–1290. doi: 10.1038/2101289a0. [DOI] [PubMed] [Google Scholar]

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