Summary
Ultrastructural observations of the giant axon of Myxicola infundibulum reveal that the axoplasm contains neurofilaments, a few neurotubules and mitochondria. Finger-like projections issuing from the glial cells of the sheath encircle the giant axon at various angles. The space between the axolemma and sheath is 125 Å. Branches of the giant axon are also surrounded by a glial sheath as they course through the neuropil. Some branches of the giant axon seem to fuse with certain neurons, creating a syncytial arrangement between the giant axon and these neurons.
Many small nerve fibers course longitudinally in the neuropil of the nerve cord. Most of these axons are separated from each other by a space of 200 Å without intervening glial processes. Synapses in the neuropil have both clear 600 Å vesicles and larger dense core vesicles suggesting chemical transmission. Some, but not all, of the synaptic areas show thickened membranes and dense material in the synaptic cleft.
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Amoroso, E. C., Baxter, M. I., Chiquoine, A. D., Nisbet, R. H.: The fine structure of neurons and other elements in the nervous system of the giant African land snail, Archachatina marginata. Proc. roy. Soc. B 160, 167–180 (1964).
Batham, E. J.: Infoldings of nerve fiber membranes in opisthobranch mollusc Aplysia californica. J. biophys. biochem. Cytol. 9, 490–492 (1967).
Binstock, L., Goldman, L.: Giant axon of Myxicola: some membrane properties as observed under voltage clamp. Science 158, 1467–1469 (1967).
Binstock, L., Goldman, L.: Current- and voltage-clamped studies on Myxicola giant axons: effect of tetrodotoxin. J. gen. Physiol. 54, 730–740 (1969).
Bullock, T. H., Horridge, G. A., Eds: Structure and function in the nervous system of invertebrates, 2 vols., 2517 pp. San Francisco: Freeman 1965.
Coggeshall, R. E.: A fine structural analysis of the ventral nerve cord and associated sheath of Lumbricus terrestris L. J. comp. Neurol. 125, 393–438 (1965).
Coggeshall, R. E., Fawcett, D. W.: The fine structure of the central nervous system of the leech, Hirudo medicinalis. J. Neurophysiol. 27, 229–289 (1964).
Geren, B. B., Schmidt, F. D.: The structure of the Schwann cell and its relation to the axon in certain invertebrate nerve fibers. Proc. nat. Acad. Sci. (Wash.) 40, 863–870 (1954).
Gerschenfeld, H. M.: Observations on the ultrastructure of synapses in some pulmonate molluscs. Z. Zellforsch. 60, 258–275 (1963).
Gilbert, D. S., Shaw, T. I.: Extrusion and perfusion of the giant nerve fibre of Myxicola infundibulum. J. Physiol. (Lond.) 204, 28P-29P (1969).
Hess, A.: The fine structure of nerve cells and fibers, neuroglia and sheaths of the ganglion chain in the cockroach, Periplaneta americana. J. biophys. biochem. Cytol. 4, 731–742 (1958).
Hidaka, T., Ito, Y., Tashiro, N.: Neuromuscular transmission in the longitudinal layer of somatic muscle in the earthworm. J. exp. Biol. 50, 417–430 (1969a).
Hidaka, T., Kuriyama, H., Yamamoto, T.: The mechanical properties of the longitudinal muscle in the earthworm. J. exp. Biol. 50, 431–443 (1969b).
Horridge, G. A.: Analysis of the rapid response of Nereis and Harmothoë (Annelida). Proc. roy. Soc. B 150, 245–262 (1959).
Krasne, F.: Escape from recurring tactile stimulation in Branchiomma vesiculosum. J. exp. Biol. 42, 307–322 (1965).
Levi, J. U., Cowden, R. R., Collins, G. H.: The microscopic anatomy and ultrastructure of the nervous system in the earthworm (Lumbricus sp.) with emphasis on the relationship between glial cells and neurons. J. comp. Neurol. 127, 489–510 (1966).
Merker, G., Vaupel-Von Harnack, M.: Zur Feinstruktur des „Gehirns“ und der Sinnesorgane von Protodrilus ribropharyngeus Jaegersten (Archiannelida). Z. Zellforsch. 81, 221–239 (1967).
Nicol, J. A. C.: The giant nerve fibers in the central nervous system of Myxicola (Polychaeta, Sabellidae). Quart. J. micr. Sci. 89, 1–45 (1948a).
Nicol, J. A. C.: The giant axons of annelids. Quart. J. Biol. 23, 291–323 (1948b).
Nicol, J. A. C., Whitteridge, D.: Conduction in giant axon of Myxicola infundibulum. Physiol. comp. Oecol. 4, 107–117 (1955).
Remler, M., Selverston, A. I., Kennedy, D.: Lateral giant fibers of crayfish: location of somata by dye injection. Science 162, 281–283 (1968).
Roberts, M. V. B.: Giant fibre reflex of the earthworm. Nature (Lond.) 186, 167 (1960).
Roberts, M. V. B.: The rapid response of Myxicola infundibulum (Grube). J. marine biol. Ass. 42, 527–539 (1962a).
Roberts, M. V. B.: The giant fibre reflex of the earthworm Lumbricus terrestris L. I. The rapid response. J. exp. Biol. 39, 219–227 (1962b).
Smith, D. S., Treherne, J. E.: The electronmicroscopic localization of cholinesterase activity in the central nervous system of an insect, Periplaneta americana L. J. Cell Biol. 26, 445–465 (1965).
Stretton, A. O. W., Kravitz, E. A.: Neuronal geometry: determination with a technique of intracellular dye injection. Science 162, 132–134 (1968).
Stuart, A. E.: Excitatory and inhibitory motoneurons in the central nervous system of the leech. Science 165, 817–819 (1969).
Villegas, G. M., Villegas, R.: The ultrastructure of the giant nerve fibre of the squid: Axon-Schwann cell relationship. J. Ultrastruct. Res. 3, 362–373 (1960).
Villegas, G.M., Villegas, R.: Ultrastructural studies of the squid nerve fibers. J. gen. Physiol. 51, 44s-60s (1968).
Villegas, G. M., Villegas, R., Dipolo, R., Villegas, J.: Non-electrolyte permeability, sodium influx, electrical potentials and axolemma ultrastructure in squid axons of various diameters. J. gen. Physiol. 57, 623–637 (1971).
Wilson, D. M.: The nervous control of movement in annelids. J. exp. Biol. 37, 46–56 (1960).
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This study was supported in part by PHS NS-07740 to R.L.P., J.A.B. is a NDEA Predoctoral Fellow in the Department of Physiology.
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Wells, J., Besso, J.A., Boldosser, W.G. et al. The fine structure of the nerve cord of Myxicola infundibulum (annelida, polychaeta). Z.Zellforsch 131, 141–148 (1972). https://doi.org/10.1007/BF00306923
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DOI: https://doi.org/10.1007/BF00306923