Summary
The surface of the external glial layer of the isocortex in the human temporal lobe is generally slightly undulated, with a few protrusions and indentations. The surface is formed by an uninterrupted basement membrane which is continuous over the surface no matter how tortuous it becomes. The overall thickness of the glial layer is generally 15 to 25 μm, but diminishes to about 5 μm immediately beneath blood vessels. It consists mainly of a variable number of stacked glial cell processes.
Two groups of cell bodies are encountered particularly in the middle and lower levels of the glial layer. Most of the cells are specialized fibrous astrocytes. They are characterized by eccentrically placed, rounded nuclei with homogeneously dispersed chromatin, and electron-lucent cytoplasm rich in filaments. Lipofuscin pigment granules occupy large areas of the perikaryon. The astroglial cells give rise to four types of processes: foot-processes, tangential and radial processes, and processes irregular in outline.
The foot-processes ascend towards the cortical surface and terminate as flat expansions spreading out immediately beneath the basement membrane. Contiguous terminal expansions are connected by gap junctions. The individual profiles are irregular in form and fit together like in a jig-saw puzzle. The plasmalemma beneath the basement membrane is underlined by a fuzzy material, which is penetrated by glial filaments. In the terminal expansions individual or groups of mitochondria are abundant.
The tangential processes are straight and slender and form a lattice within the middle and deep level of the external glial layer. They contain numerous filaments, evenly distributed or fasciculated. The remainder of the lattice is filled up by a considerable number of processes irregular in outline and varying greatly in size. They contain fewer filaments than the tangential processes, coursing in all directions, and glycogen particles. In both types of processes only a few mitochondria are present. These processes are also connected by gap junctions and desmosomes, too.
Large cytoplasmic areas of astroglial cells localized in the deepest portion of the glial layer protrude into the neuropil of the molecular layer, giving rise to several radiate processes, which extend deeper into the cortex.
The second, heterogeneous group of cell bodies is characterized by elongated nuclei, ovoid or irregular in outline, which are smaller than those of astroglial cells, and contain blocks of condensed chromatin; a thin cytoplasmic rim generating a few appendages surrounds the nucleus. The first sub-type is characterized by a nucleus with large chromatin blocks bordering the inner nuclear membrane and a medium-dense cytoplasmic matrix. The second sub-type displays smaller chromatin condensations at the inner nuclear membrane and many microtubules are scattered throughout an electron-lucent cytoplasm.
Similar content being viewed by others
References
Andres, K. H.: Zur Feinstruktur der Arachnoidalzotten bei Mammalia. Z. Zellforsch. 82, 92–109 (1967)
Blinzinger, K., Rewcastle, N. B., Hager, H.: Observations on prismatic-type mitochondria within astrocytes of the Syrian hamster brain. J. Cell Biol. 25, 293–303 (1965)
Böhme, G.: Die marginale Glia des Cortex cerebri der Ratte. Z. Zellforsch. 70, 269–278 (1966)
Bondareff, W., McLone, D. G.: The external glial limiting membrane in Macaca: ultrastructure of a laminated glioepithelium. Amer. J. Anat. 136, 277–296 (1973)
Braak, H.: Über das Neurolipofuscin in der unteren Olive und dem Nucleus dentatus cerebelli im Gehirn des Menschen. Z. Zellforsch. 121, 573–592 (1971)
Braak, H.: On the structure of the human archicortex. I. The cornu ammonis. A Golgi and pigmentarchitectonic study. Cell Tiss. Res. 152, 349–383 (1974)
Braitenberg, V., Gugliemotti, V., Sada, E.: Correlation of crystal growth with the staining of axons by the Golgi procedure. Stain Technol. 42, 277–283 (1967)
Brightman, M. W., Reese, T. S.: Junctions between intimately apposed cell membranes in the vertebrate brain. J. Cell Biol. 40, 648–677 (1969)
Caley, D. W., Maxwell, D. S.: An electron microscopic study of the neuroglia during postnatal development of the rat cerebrum. J. comp. Neurol. 133, 45–70 (1968)
Dermietzel, R.: Junctions in the central nervous system of the cat. III. Gap junctions and membrane-associated orthogonal particle complexes (MOPG) in astrocyte membranes. Cell Tiss. Res. 149, 121–135 (1974)
Duncan, D., Morales, R.: Fine structure of astrocyte mitochondria in the spinal cord of the dog, cat and monkey. Anat. Rec. 175, 519–528 (1973)
Fleischhauer, K.: Fluoreszenzmikroskopische Untersuchungen an der Faserglia. Z. Zellforsch. 51, 467–496 (1960)
Haug, H.: Die Membrana limitans gliae superficialis der Sehrinde der Katze. Z. Zellforsch. 115, 79–87 (1971)
Haug, H.: Die postnatale Entwicklung der Gliadeckschicht der Sehrinde der Katze. Eine elektronenmikroskopische Studie über die Ausbildung von Lamellenstapeln. Z. Zellforsch. 123, 544–565 (1972)
Held, H.: Über die Neuroglia marginalis der menschlichen Großhirnrinde. Mschr. Psychiat. Neurol. 26, Erg.-Heft, 360–416 (1909)
Iida, T.: Elektronenmikroskopische Untersuchungen am oberflächlichen Anteil des Gehirns bei Hund und Katze. Arch. Histol. Jap. 27, 267–285 (1966)
Janzen, R. W. Chr.: Topographische Besonderheiten im Bau der Glia marginalis des Menschen. Z. Zellforsch. 80, 570–584 (1967)
Jones, E. G.: On the mode of entry of blood vessels in the cerebral cortex. J. Anat. (Lond.) 106, 507–520 (1970)
Jones, E. G., Powell, T. P. S.: Electron microscopy of the somatic sensory cortex in the cat. II. The fine structure of layers I and II. Phil. Trans. B 257, 13–21 (1970)
King, J. S.: A light and electron microscopic study of perineuronal glial cells and processes in the rabbit neocortex. Anat. Rec. 161, 111–124 (1968)
King, J. S., Schwyn, R. C.: The fine structure of neuroglial cells and pericytes in primate red nucleus and substantia nigra. Z. Zellforsch. 106, 309–321 (1970)
Ling, E. A., Paterson, J. A., Privat, A., Mori, S., Leblond, C. P.: Investigation of glial cells in semithin sections. I. Identification of glial cells in the brain of young rats. J. comp. Neurol. 149, 43–72 (1973)
Lopes, C. A. S., Mair, W. G. P.: Ultrastructure of the outer cortex and the pia mater in man. Acta neuropath. (Berl.) 28, 79–86 (1974)
Matthews, M. A.: Microglia and reactive “M” cells of degenerating central nervous system: does similar morphology and function imply a common origin? Cell Tiss. Res. 148, 477–491 (1974)
Morales, R., Duncan, D.: Prismatic and other unusual arrays of mitochondria cristae in astrocytes of cats and hamsters. Anat. Rec. 171, 545–558 (1971)
Mori, S., Leblond, C. P.: Identification of microglia in light and electron microscopy. J. comp. Neurol. 135, 57–80 (1969a)
Mori, S., Leblond, C. P.: Electron microscopic features and proliferation of astrocytes in the Corpus callosum of the rat. J. comp. Neurol. 137, 197–226 (1969b)
Mori, S., Leblond, C. P.: Electron microscopic identification of three classes of oligodendrocytes and a preliminary study of their proliferative activity in the Corpus callosum of young rats. J. comp. Neurol. 139, 1–30 (1970)
Morse, D. E., Low, F. N.: The fine structure of the pia mater of the rat. Amer. J. Anat. 133, 349–354 (1972)
Niessing, K.: Über systemartige Zusammenhänge der Neuroglia im Großhirn und über ihre funktionelle Bedeutung. Gegenbaurs Morph. Jb. 78, 537–584 (1936)
Obersteiner, H.: Über das hellgelbe Pigment in den Nervenzellen und das Vorkommen weiterer fettähnlioher Körper im Zentralnervensystem. Arb. neurol. Inst. Wien 10, 245–274 (1903)
Palay, S. L., Chan-Palay, V.: Cerebellar cortex. Cytology and organization. Berlin-Heidelberg-New York: Springer 1974
Pease, D. C., Molinari, S.: Electron microscopy of muscular arteries, pial vessels of the cat and monkey. J. Ultrastruct. Res. 3, 447–468 (1960)
Pease, D. C., Schultz, R. L.: Electron microscopy of rat cranial meninges. Amer. J. Anat. 102, 301–322 (1958)
Peters, A., Palay, S. L., Webster, H. de F.: The fine structure of the nervous tissue. The cells and their processes. New York-Evanston-London: Hoeber Medical Division-Harper and Row 1970
Peters, A., Vaughn, J. E.: Microtubules and filaments in the axons and astrocytes of early postnatal rat optic nerves. J. Cell Biol. 32, 113–119 (1967)
Ramon y Cajal, S.: Histologie du système nerveux de l'homme et des vertébrés. Paris: Maloine 1909. Reprinted 1952–1955, Madrid: Consejo superior de Investigaciones cientificas.
Ramsey, H. J.: Fine structure of the surface of the cerebral cortex of human brain. J. Cell Biol. 26, 323–333 (1965)
Rascol, M., Izard, J.: Ultrastructures des granulationes de Pacchioni de la méninge humaine chez l'adulte. J. Microscopie 8, 1017–1030 (1969)
Rascol, M., Izard, J.: La jonction cortico-pie-mérienne et la pénétration des vaisseaux dans le cortex cérébral chez l'homme. Structure et ultrastructure. Z. Zellforsch. 123, 337–355 (1972)
Retzius, G.: Die Neuroglia des Gehirns bei Menschen und Säugethieren. Biol. Unters. 6 (1893/94). Cit. from Niessing, K. (1936)
Reynolds, E. S.: The use of lead citrate at high pH as an electron-opaque stain in electron microscopy. J. Cell Biol. 17, 208–211 (1963)
Richardson, K. C., Jarett, L., Finke, E. H.: Embedding in epoxy resins for ultrathin sectioning in electron microscopy. Stain Technol. 35, 313–323 (1960)
Sotelo, C.: Ultrastructural aspects of the cerebellar cortex of the frog. In: Neurobiology of cerebellar evolution and development (ed.: R. Llinás), p. 327–371. Chicago: Amer. Med. Assoc. Education and Research Foundation 1969
Tani, E., Nishiura, M., Higashi, N.: Freeze-fracture studies of gap junctions of normal and neoplastic astrocytes. Acta neuropath. (Berl.) 26, 127–138 (1973)
Thomas, H.: Licht-und elektronenmikroskopische Untersuchungen an den weichen Hirnhäuten und den Pacchionischen Granulationen des Menschen. Z. mikr.-anat. Forsch. 75, 270–327 (1966)
Tusques, J., George, Y., Couderc, M., Roch, M.: Ultrastructure de l'oligodendroglie de l'écorce cérébrale humaine. Bull. Ass. Anat. (Nancy) 57, 939–948 (1973)
Vaughn, J. E.: An electron microscopic analysis of gliogenesis in rat optic nerves. Z. Zellforsch. 94, 293–324 (1969)
Vaughn, J. E., Peters, A.: Electron microscopy of the early postnatal development of fibrous astrocytes. Amer. J. Anat. 121, 131–152 (1967)
Wolff, J.: Elektronenmikroskopische Untersuchungen über Struktur und Gestalt von Astrozytenfortsätzen. Z. Zellforsch. 66, 811–828 (1965)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Braak, E. On the fine structure of the external glial layer in the isocortex of man. Cell Tissue Res. 157, 367–390 (1975). https://doi.org/10.1007/BF00225527
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF00225527