Respiration-related discharge of hyoglossus muscle motor units in the rat

Gregory L. Powell, Amber Rice, Seres J. Bennett-Cross, Ralph F. Fregosi

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Although respiratory muscle motor units have been studied during natural breathing, simultaneous measures of muscle force have never been obtained. Tongue retractor muscles, such as the hyoglossus (HG), play an important role in swallowing, licking, chewing, breathing, and, in humans, speech. The HG is phasically recruited during the inspiratory phase of the respiratory cycle. Moreover, in urethane anesthetized rats the drive to the HG waxes and wanes spontaneously, providing a unique opportunity to study motor unit firing patterns as the muscle is driven naturally by the central pattern generator for breathing. We recorded tongue retraction force, the whole HG muscle EMG and the activity of 38 HG motor units in spontaneously breathing anesthetized rats under low-force and high-force conditions. Activity in all cases was confined to the inspiratory phase of the respiratory cycle. Changes in the EMG were correlated significantly with corresponding changes in force, with the change in EMG able to predict 53-68% of the force variation. Mean and peak motor unit firing rates were greater under high-force conditions, although the magnitude of discharge rate modulation varied widely across the population. Changes in mean and peak firing rates were significantly correlated with the corresponding changes in force, but the correlations were weak (r2 = 0.27 and 0.25, respectively). These data indicate that, during spontaneous breathing, recruitment of HG motor units plays a critical role in the control of muscle force, with firing rate modulation playing an important but lesser role.

Original languageEnglish (US)
Pages (from-to)361-368
Number of pages8
JournalJournal of neurophysiology
Issue number2
StatePublished - Jan 15 2014


  • Breathing
  • Electrophysiology
  • Hypoglossal
  • Tongue muscles

ASJC Scopus subject areas

  • Neuroscience(all)
  • Physiology


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