Site of motor pathway excitation during cervical spinal stimulation.

In a set of 25 normal subjects the probable site of activation of the motor pathway was looked for using transcutaneous cervical spinal stimulation. The motor conduction time in the fastest fibres between the "spinal cord" and the wrist reached 10.79 (SD 1.17) ms when using this technique and this value was compared to the same parameter obtained with other methods: F wave mean conduction time in the established distance was 11.0 (SD 0.96) ms; the conversion of sensory to motor conduction showed 11.0 (SD 1.1) ms and H wave 10.97 (SD 1.03) ms. The conduction time through the fastest motor fibres with the spinal stimulation corresponds to the activation of the alpha-motoneuron axons near their bodies. When interpreting the results of the cortical and spinal stimulation, it is necessary to take this fact into account.