Absolute refractory period of human nerve fibres during postnatal myelination

In order to study the absolute refractory period of a given group of nerve fibres during development we measured absolute refractory periods and conduction velocities of motor fibres and the most excitable fibres in the human ulnar nerve of newborns, children and adults. In each group of nerve fibres absolute refractory period was not correlated to conduction velocity (i.e. fibre diameters) and was rather constant during development. However, absolute refractory period of the most excitable fibres was smaller than absolute refractory period of motor fibres independently of the subject's age. Thus, it appears that already at birth, absolute refractory period is characteristic for a given group of nerve fibres.