Neuron Conduction Velocity Calculator
Calculate action potential conduction speed for myelinated and unmyelinated nerve fibers from axon diameter.
Compare propagation time over any nerve length.
Nerve impulses travel along axons as action potentials — brief reversals of membrane polarity. How fast they travel depends critically on axon diameter and whether the axon is myelinated.
Unmyelinated axons (Type C fibers). Action potentials propagate by local circuit currents spreading continuously along the membrane. Velocity scales with the square root of diameter:
v ≈ 0.57 × sqrt(d) m/s
where d is the axon diameter in micrometers. Typical velocities: 0.5-2 m/s. These fibers carry pain (slow, burning), temperature, and autonomic signals.
Myelinated axons (A and B fibers). Myelin sheath acts as electrical insulation. The action potential jumps from one node of Ranvier to the next (saltatory conduction), dramatically increasing speed while reducing energy cost. Velocity scales linearly with diameter:
v ≈ 6 × d m/s
where d is the total fiber diameter (axon + myelin) in micrometers. Typical velocities: 3-120 m/s for B and A fibers.
Why the difference matters. Touch and proprioception (A-alpha, A-beta fibers, 6-20 µm) conduct at 36-120 m/s. A tap on your knee reaches your spinal cord in ~10 ms. Slow pain signals (C fibers, 0.5-1.5 µm) travel at 0.5-2 m/s. A sting in your foot takes 200-400 ms to register as slow, burning pain after the initial sharp sensation.
Demyelinating diseases like multiple sclerosis slow or block conduction in myelinated fibers, causing the characteristic patchy neurological deficits.