Intro to Neurobiology Membrane excitability The action potential Intro to Neurobiology Outline Passive and active conduction in neurons Action potential phenomenology Participating currents Voltage clamp experiments Voltage dependence: activation and inactivation Qualitative mechanistic description of action potential phenomenology Intro to Neurobiology Reminder: passive conduction Intro to Neurobiology Propagation of action potentials Depends on passive membrane properties Conduction velocity increases with And decreases with Intro to Neurobiology Improving conduction velocity Increased diameter (squid) Problem: limited space Myelin Increases R m Decreases C Allows energetically efficient signaling Intro to Neurobiology Myelin PNS-Schwann cells 1 per internode CNS- Oligodendrocytes 1 per several axonal processes membrane wraps Cytoplasm is squeezed out Intro to Neurobiology Saltatory conduction Passive conductance in internodes Active AP regeneration in nodes of Ranvier Intro to Neurobiology Differential channel constitution Intro to Neurobiology Demyelination Slowing of conduction Desynchronization of different fibers Conduction block Complete At high frequencies Intro to Neurobiology Conduction velocity Mylinated: A m/s A30-80m/s a5-30m/s Unmylinated: C