Figure 4. Examples of early and late excitation of commissural neurones by group II afferents, attributable to monosynaptic and disynaptic actions.

A–C and D–F, illustrate records from two different commissural neurones respectively. A and D show EPSPs evoked by two and three stimuli applied to the quadriceps nerve (Q) (upper traces) and cord dorsum potentials (lower traces). B and E show extracellular spikes, recorded just before penetration of the neurones, with cord dorsum potentials. Note the likely disynaptically induced EPSPs (the second of the dotted lines) following the monosynaptically evoked ones (first dotted lines) after the second stimulus. C and F, antidromic activation from the contralateral GS motor nucleus (co GS MN) and collision between synaptically and antidromically induced extracellular spikes confirming antidromic activation; two and three superimposed records. Voltage calibrations are 0.2 mV for A and B and 0.5 mV for D and E.