Non-rapid eye movement sleep activation occurs during NREM that is comparable to the type that occurs during REM. It is this sub-cortical activation that results in dreaming during the NREM stage during the morning hours. During non-REM sleep, the tonic drive to most respiratory muscles of the upper airway is inhibited. This has two consequences: However, because the diaphragm is largely driven by the autonomous system, it is relatively spared of non-REM inhibition. As such, the suction pressures it generates stay the same. This narrows the upper airway during sleep, increasing resistance and making airflow through the upper airway turbulent and noisy. For example,
Eye movement can make the photoreceptors or the ganglion cells become unresponsive; on the other hand a changing stimulus will not. Therefore, the random eye movement constantly changes the stimuli that fall on the photoreceptors and the ganglion cells, making the image more clear. Saccades are the rapid movement of eyes that is used while scanning a visual scene. In our subjective impression, the eyes do not move smoothly across the printed page during reading. Instead, our eyes make short and rapid movements called "saccades". During each "saccade" the eyes move as fast as they can and the speed cannot be consciously