Summary
Membrane specialisations have been found on neurones in embryos of the clawed toad Xenopus laevis. The specialisations have been called dense membrane knobs and consist of an outpushing of the plasma membrane with a slight increase in its density. The out-pushing forms a spherical knob with an amorphous dense core and a total diameter of 500 to 600 Å. The knobs are found on axons and dendrites both in the spinal cord and peripherally.
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Roberts, A., Hayes, B.P. A new membrane organelle in developing amphibian neurones. Cell Tissue Res. 154, 103–108 (1974). https://doi.org/10.1007/BF00221074
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DOI: https://doi.org/10.1007/BF00221074