Discharge Patterns Of Tensor Palatini Motor Units During Sleep Onset

School of Psychological Science, University of Melbourne, Parkville, Australia.
Sleep (Impact Factor: 4.59). 05/2012; 35(5):699-707. DOI: 10.5665/sleep.1834
Source: PubMed


Upper airway muscles such as genioglossus (GG) and tensor palatini (TP) reduce activity at sleep onset. In GG reduced muscle activity is primarily due to inspiratory modulated motor units becoming silent, suggesting reduced respiratory pattern generator (RPG) output. However, unlike GG, TP shows minimal respiratory modulation and presumably has few inspiratory modulated motor units and minimal input from the RPG. Thus, we investigated the mechanism by which TP reduces activity at sleep onset.
The activity of TP motor units were studied during relaxed wakefulness and over the transition from wakefulness to sleep.
Sleep laboratory.
Nine young (21.4 ± 3.4 years) males were studied on a total of 11 nights.
Sleep onset.
Two TP EMGs (thin, hooked wire electrodes), and sleep and respiratory measures were recorded. One hundred twenty-one sleep onsets were identified (13.4 ± 7.2/subject), resulting in 128 motor units (14.3 ± 13.0/subject); 29% of units were tonic, 43% inspiratory modulated (inspiratory phasic 18%, inspiratory tonic 25%), and 28% expiratory modulated (expiratory phasic 21%, expiratory tonic 7%). There was a reduction in both expiratory and inspiratory modulated units, but not tonic units, at sleep onset. Reduced TP activity was almost entirely due to de-recruitment.
TP showed a similar distribution of motor units as other airway muscles. However, a greater proportion of expiratory modulated motor units were active in TP and these expiratory units, along with inspiratory units, tended to become silent over sleep onset. The data suggest that both expiratory and inspiratory drive components from the RPG are reduced at sleep onset in TP.

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    • "Further, they may be phasic (Inspiratory Phasic or Expiratory Phasic) without a tonic component. While these discharge patterns have been observed in the motor units of all upper airway muscles studied, the distribution of the different patterns varies (Chanaud and Ludlow, 1992; Nicholas et al., 2012; Saboisky et al., 2006). Critically, changes in respiratory drive, such as occurs with changes in sleep-wake state Wilkinson et al., 2008) or hypercapnia (Nicholas et al., 2010) for example, differentially affect motor units with different discharge patterns, presumably reflecting changes in the pattern of pre-motor inputs. "
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