After Mork has gone through one full sleep cycle, his heart beats faster, his breathing grows fast and irregular, and his closed eyes begin to move back and forth. A researcher who is monitoring Mork’s EEG activity will most likely see __________ waves.

When Mork has gone through one full sleep cycle, entering a phase where his heart rate increases, his breathing grows fast and irregular, and his closed eyes begin to move back and forth, he is likely entering the Rapid Eye Movement (REM) sleep stage. During REM sleep, the researcher monitoring EEG (electroencephalogram) activity will most likely observe brain waves that are similar to those seen in wakefulness, which are predominantly beta waves. These waves are low amplitude and high frequency, and are associated with active, alert mental states. Some theta waves may also be present during REM sleep. This brain activity corresponds with the vivid dreaming that commonly occurs during REM sleep.

Sleep is categorized into two main types: Non-REM (NREM) and REM sleep. NREM sleep is further divided into stages 1, 2, and 3, each with distinctive patterns of brain waves.

1. Stage 1 NREM sleep is a light sleep where one drifts in and out of sleep and can be awakened easily. In this stage, the EEG shows theta waves, which are slower in frequency and larger in amplitude than wakeful alpha waves.

2. Stage 2 NREM sleep involves a reduction in heart rate and body temperature, with EEG showing sleep spindles and K complexes.

3. Stage 3 NREM sleep, also known as deep sleep or slow-wave sleep, is characterized by the presence of delta waves, which are high amplitude, low-frequency waves. This is a restorative sleep stage where the body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system.

REM sleep is the deepest sleep stage and, as mentioned above, is characterized by beta and theta wave patterns on an EEG. It is during this stage that intense dreaming occurs, owing to the heightened brain activity. The body becomes temporarily paralyzed during REM sleep, which prevents one from physically acting out their dreams. As the sleep cycle progresses through the night, the proportion of REM sleep increases while that of NREM sleep decreases. Adults typically experience four to six sleep cycles per night, each lasting approximately 90 minutes. Understanding sleep physiology is important for recognizing sleep disorders and their implications on overall health.