E3 Impulse propagation (cable theory and Saltatory conduction)

Title

Nerve impulse propagation along the axon is described by the cable theory, which treats the axon as a distributed circuit with internal axial resistance, membrane resistance, and membrane capacitance per unit length. The ratio between membrane resistance and axial resistance defines the length constant (lambda), which determines how much a passive signal is spatially attenuated, while the product of membrane resistance and capacitance defines the time constant (tau_m) inherited from E01. In unmyelinated fibers the conduction velocity scales approximately with the root of the axonal diameter, while in myelinated fibers the conduction is saltatory (the impulse jumps from node of Ranvier to node of Ranvier), which causes the velocity to scale linearly with the diameter and be much greater for the same caliber. The conduction safety factor compares the available current generated at an active node with the threshold current needed to excite the next segment, ensuring reliable propagation of the action potential described in E02.

ID:4261