Evidence for excitation of the human lower limb motoneurones by group II muscle afferents

Exp Brain Res. 1996 May;109(2):357-60. doi: 10.1007/BF00231793.


The possibility was investigated that stimulation of high-threshold afferents in the common peroneal nerve (CPN) evokes excitation of quadriceps (Q) motoneurones in humans. Effects of conditioning stimuli at motor threshold (1 x MT) and at higher intensities were compared on both the Q H-reflex and the post-stimulus time histogram (PSTH) of individual motor units. At 1 x MT, CPN stimulation evokes a facilitation, which has been shown to be caused by an interneuronally mediated group I excitation. Increasing the CPN stimulus intensity above 2 x MT caused this early excitation to increase and a later facilitation to appear both in the H-reflex and in the PSTH of single units. The later excitation had its threshold between 2 and 3 x MT, and it appeared 4-8 ms after the group I-induced excitation. The higher threshold and the longer latency suggest that this excitation is evoked by afferents with a smaller diameter than group I afferents, and group II afferents meet this criterion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Afferent Pathways / physiology*
  • Female
  • H-Reflex / physiology*
  • Humans
  • Male
  • Middle Aged
  • Motor Neurons / physiology*
  • Muscles / physiology*
  • Reaction Time / physiology*