Key pointsr In peripheral myelinated axons of mammalian spinal motor neurons, Ca 2+ influx was thought to occur only in pathological conditions such as ischaemia. influx, some active in normally-myelinated axons (T-type channels, NCX), others active only when exposed by myelin disruption (L-type channels). The modest axoplasmic peri-nodal [Ca 2+ ] elevations measured in intact motor axons might mediate local responses to axonal activation. The larger [Ca 2+ ] elevations measured after myelin disruption might, over time, contribute to the axonal degeneration observed in peripheral demyelinating neuropathies.