| Comments |
P.R511 right column 2nd paragraph: "It should be noted that, in many invertebrate species, certain axons are covered with what are best characterized as ‘experimental’ forms of myelin [refs 5–7], and indeed, these axons conduct at much higher velocities than their diameters would otherwise permit if they were bare. These devices work well for organisms with multiple ganglia, but must have been unsatisfactory for vertebrates, which, because of the physical constraints imposed by the skull and vertebral column,
evolved instead a complex program to ensheath axons within a tightly compacted insulating membrane: the vertebrate myelin sheath that enables action potentials to propagate at 50 to 100 m/sec along axons with a diameter similar to most invertebrates (Supplemental Results 1 in the Supplemental data available online)." |