Recruitment of single motor units in the human blink reflex

The recruitment of single motor units (MU) in the early (R1) and late (R2) components of the electrically evoked human blink reflex (BR) was studied using bipolar needle electrodes with a limited take-off area. It could be shown that the same MUs can discharge in R1 and R2 of a BR as well as during voluntary eyelid contraction. At repetitive stimulation (1 Hz), facilitation of MU discharges in R1 and habituation in R2 became apparent. The visible reflex eyelid contraction may mainly be due to repetitive MU discharges in R2. The discharges of the same MUs in R1, however, contribute to it and shorten the latency between stimulus and reflex response.