Sleep

• Difference in brain activity help to characterise sleep stages. This brain activity can be measured using an EEG (electroencephalograph).
• The first stage is NREM sleep, which has four sub-stages.
• Stage 1 - light sleep, muscles are less active, eye movements slow, going through alpha and theta brainwaves.
• Stage 2 - more relaxed than Stage 1, body temperature drops, heart rate slows down, breathing becomes slower and deeper, theta waves.
• Stage 3 - deepest level of sleep, hard to wake up from this state, going through delta waves.
• Stage 4 - REM sleep, eyes move rapidly back and forth under closed eyelids, rapid breathing, irregular heartbeat, blood pressure increases, going through beta and theta waves.
• Stages 3 & 4 - deepest level of sleep, most difficult to wake up from, going through delta waves.
• Sleep deprivation refers to getting too little sleep or having poor quality sleep.
• Rapid Eye Movement (REM) sleep occurs every 90 minutes during sleep. It lasts between 5 and 30 minutes at a time. During REM sleep, we experience vivid dreams. The eyes move rapidly behind closed eyelids, but other muscle groups become paralyzed so that people do not act out their dreams. Heartbeat increases, blood pressure rises, and breathing quickens. Brain wave patterns resemble those seen when awake.
• Stage 4 - very little movement or muscle tone, no eye movement, going through delta waves.
• Stage 1 & 2 are REM sleep. During REM sleep, incoming sensory information is blocked ( sensory blockade). In REM signals from pons shut off neurons in the spinal cord preventing movement.
• Circadian Rhythm is the human biological clock that controls the sleep-wake cycle and other biological processes that occur in 24 hrs. The suprachiasmatic nuclei (SCN) found in the middle of the brain controls the circadian rhythm and is often triggered by external clues like light.
• Body temperature increases when you wake up and decreases when you go to sleep. Jet lag and shift work can affect your sleep wake cycle.
• Ultradian rhythms are rhythms that occur in a period less than 24 hours, such as heart beat, blood circulation and appetite.
• Our internal biological clock is endogenous (internal pacemakers - circadian and ultradian rhythms) and it keeps our biological rhythms synchronised. Under stress, adrenocorticotropic hormone (ATCH) in the pituitary gland releases cortisol, which causes alertness affecting sleep. Melatonin is a hormone produced in the pineal gland, it is triggered by darkness. Melatonin can be used as medication for jet lag and insomnia.