Non-REM Muscle Movements
The tonic drive to the majority of the upper airway’s respiratory muscles is repressed during non-REM sleep, with the following consequences –
- Due to the intracellular calcium levels being lowered, weakened muscle contractions are caused by rhythmic innervation. Motoneurons are hyperpolarized by tonic innervation being removed.
- There’s a ‘floppiness’ in the upper airway.
The diaphragm is typically driven by the autonomous system and is therefore normally spared non-REM inhibition, and as such, the suction pressure generated stays the same. The upper airway is thus narrowed during sleep, which increases resistance and makes upper airway airflow noisy and turbulent. As we know, we determine that a person is asleep by listening to their breathing: their breathing becomes distinctly louder once they fall asleep. So, it’s not surprising that the upper airway’s increased tendency to collapse while breathing during sleep leads to snoring, which is simply the tissues vibrating in the upper airway. For overweight people, this problem is aggravated when they sleep on their back because excess fat tissue can easily push down and close the airway. This can ultimately lead to sleep apnea.
Each sleep stage serves a unique role in brain and body restoration. There are many sleep deprivation studies that have demonstrated that depriving subjects of specific sleep stages has an adverse effect on body and brain functions.