title: Tuning of Ranvier node and internode properties in myelinated axons to adjust action potential timing.
abstract: Action potential timing is fundamental to information processing; however, its determinants are not fully understood. Here we report unexpected structural specializations in the Ranvier nodes and internodes of auditory brainstem axons involved in sound localization. Myelination properties deviated significantly from the traditionally assumed structure. Axons responding best to low-frequency sounds had a larger diameter than high-frequency axons but, surprisingly, shorter internodes. Simulations predicted that this geometry helps to adjust the conduction velocity and timing of action potentials within the circuit. Electrophysiological recordings in vitro and in vivo confirmed higher conduction velocities in low-frequency axons. Moreover, internode length decreased and Ranvier node diameter increased progressively along the distal axon segments, which simulations show was essential to ensure precisely timed depolarization of the giant calyx of Held presynaptic terminal. Thus, individual anatomical parameters of myelinated axons can be tuned to optimize pathways involved in temporal processing.
authors: Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität Munich, Munich D-82152, Germany.|Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK.
authors: Marc C
authors: MC
authors: Ford
authors: Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität Munich, Munich D-82152, Germany.
authors: Olga
authors: O
authors: Alexandrova
authors: Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK.
authors: Lee
authors: L
authors: Cossell
authors: Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität Munich, Munich D-82152, Germany.
authors: Annette
authors: A
authors: Stange-Marten
authors: Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität Munich, Munich D-82152, Germany.
authors: James
authors: J
authors: Sinclair
authors: Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität Munich, Munich D-82152, Germany.
authors: Conny
authors: C
authors: Kopp-Scheinpflug
authors: Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität Munich, Munich D-82152, Germany.
authors: Michael
authors: M
authors: Pecka
authors: Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK.
authors: David
authors: D
authors: Attwell
authors: Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität Munich, Munich D-82152, Germany.
authors: Benedikt
authors: B
authors: Grothe
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001369:Axons / Q000502:physiology*; D001933:Brain Stem / Q000502:physiology; D017626:Cochlear Nucleus / Q000502:physiology*; D003198:Computer Simulation; D005849:Gerbillinae; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008959:Models, Neurological; D009186:Myelin Sheath / Q000502:physiology; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology*; D017729:Presynaptic Terminals / Q000502:physiology; D011901:Ranvier's Nodes / Q000502:physiology*; D013017:Sound Localization / Q000502:physiology*