# What is the actual speed of nerve impulses in humans?

For an undergrad assignment I read a biology paper that mentioned the speed of nerve imuplses to be 440 km/h in myelinated fibers. However, our biology teacher told us that this reported conduction speed is not true. So my question is:

What is the actual speed of myelinated fibers?

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Commented Jun 17, 2017 at 19:03
• I saw in a few books that the speed of the myelinated fibre was 120m/s in human beings but then after sometime I saw the speed of the myelinated fibres was 440km/h in bbc documentary which is similar to 120m/s but one speed is in (m/s) and the other is in (km/h), when I convert the 120m/s into km/h so I got 432km/h therefore I needed to be sure that the error of 8km/h in 440km/h and 432km/h does not matter so I can proof it to my Teacher, I hope that you understand my question. Commented Jun 17, 2017 at 19:50

A conduction velocity of 440 km/h is possible in thick, myelinated fibers. However, this number is probably more representative of the upper range of conduction velocities, rather than a conservative average.

Background
First off, there are a heap of variables that affect neural conduction velocities (in myelinated fibers) in complex ways (Waxman, 1980), including but not limited to:

• axon diameter;
• myelin thickness;
• internode distance;
• temperature;
• axonal milieu;
• age of the subject.

Having said that, in humans myelinated, thin A-delta fibers the average conduction speed was established at 19 m/s (Gyberls et al, 1983), or 68 km/h. A range of pain-conducting fibers exist, with different diameters. As a result, they range in their conduction velocities from 0.5 m/s (2 km/h for thin C-type fibers) to 120 m/s (432 km/h for thick A-alpha type fibers).

Hence, the 440 km/h is certainly possible in thick myelinated fibers. Note I just highlighted pain-conducting fibers here as an example, and other classes of neurons may feature even faster conduction in their axons.