How fast do nerve signals travel? Up to 120 m/s

Nerve impulses in your fastest, myelin-wrapped fibres travel at up to about 120 metres per second (roughly 430 km/h), while the thinnest unmyelinated fibres manage only about 1 metre per second, walking pace. The speed depends on two things: how thick the axon is, and whether it is insulated with myelin.

The slow, bare C fibres, under a micron across, carry pain and temperature from the skin. The thickest myelinated axons serve touch and pressure sensors and the motor neurons that move muscles.

Fibre	Conduction speed
Fastest myelinated fibres	up to about 120 m/s
Thick myelinated axons (touch, pressure, motor neurons)	more than 100 m/s
Bare C fibres (pain, temperature)	about 1 m/s

Myelin works through saltatory conduction. The sheath leaves tiny gaps, the nodes of Ranvier, where almost all the axon’s sodium channels are packed, so the signal regenerates only at each node and effectively jumps between them. In a myelinated fibre, speed rises in proportion to diameter; in a bare one, only with its square root. To match a 20-micrometre myelinated fibre, a bare axon would need to be several centimetres thick, and without myelin your spinal cord would have to be several metres across.

How the speed was first measured

In 1850, physiologist Hermann von Helmholtz timed signals along frog nerves, then turned to people. He gave subjects a weak shock and asked them to react as fast as possible, comparing a shock at the big toe with one at the base of the spine, and a finger with the neck. The differences gave 62.1 and 61.0 m/s, about twice the speed in frogs.

A sensation travels “to the brain with a speed of circa 60 Meter (180 feet) [per second].” — Hermann von Helmholtz, 1850

Why it matters: when myelin is damaged, signals slow or fail. That is what happens in multiple sclerosis in the brain and spinal cord, and in Guillain-Barré syndrome in the peripheral nerves.