Key points In peripheral myelinated axons of mammalian spinal motor neurons, Ca2+ influx was thought to occur only in pathological conditions such as ischaemia. Using Ca2+ imaging in mouse large motor axons, we find that physiological stimulation with trains of action potentials transiently elevates axoplasmic [Ca2+] around nodes of Ranvier. These stimulation‐induced [Ca2+] elevations require Ca2+ influx, and are partially reduced by blocking T‐type Ca2+ channels (e.g. mibefradil) and by blocking the Na+/Ca2+ exchanger (NCX), suggesting an important contribution of Ca2+ influx via reverse‐mode NCX activity. Acute disruption of paranodal myelin dramatically increases stimulation‐induced [Ca2+] elevations around nodes by allowing activation of sub‐myelin L‐type (nimodipine‐sensitive) Ca2+ channels. The Ca2+ that enters myelinated motor axons during normal activity is likely to contribute to several signalling pathways; the larger Ca2+ influx that occurs following demyelination may contribute to the axonal degeneration that occurs in peripheral demyelinating diseases. Abstract Activity‐dependent Ca2+ signalling is well established for somata and terminals of mammalian spinal motor neurons, but not for their axons. Imaging of an intra‐axonally injected fluorescent [Ca2+] indicator revealed that during repetitive action potential stimulation, [Ca2+] elevations localized to nodal regions occurred in mouse motor axons from ventral roots, phrenic nerve and intramuscular branches. These [Ca2+] elevations (∼0.1 μm with stimulation at 50 Hz, 10 s) were blocked by removal of Ca2+ from the extracellular solution. Effects of pharmacological blockers indicated contributions from both T‐type Ca2+ channels and reverse mode Na+/Ca2+ exchange (NCX). Acute disruption of paranodal myelin (by stretch or lysophosphatidylcholine) increased the stimulation‐induced [Ca2+] elevations, which now included a prominent contribution from L‐type Ca2+ channels. These results suggest that the peri‐nodal axolemma of motor axons includes multiple pathways for stimulation‐induced Ca2+ 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 [Ca2+] elevations measured in intact motor axons might mediate local responses to axonal activation. The larger [Ca2+] elevations measured after myelin disruption might, over time, contribute to the axonal degeneration observed in peripheral demyelinating neuropathies.