stages of sleep & why sleep

• Coma


  An extended period of unconsciousness caused by head trauma, stroke, or disease. Low level of brain activity throughout the day, and little or no response to stimuli
• Brain death


  A condition with no sign of brain activity and no response to any stimulus
• Stage 4 Sleep


  • More than half the record includes large waves of at least a half-second duration. Stages 3 and 4 together constitute slow-wave sleep (SWS). Slow waves indicate highly synchronized neuronal activity
• Stage 1 Sleep


  • EEG dominated by irregular, jagged, low-voltage waves. Overall brain activity is less than in relaxed wakefulness but higher than in other sleep stages
• REM Sleep


  • Characterized by its combination of deep and light sleep attributes, associated with physiological changes such as erections in males and vaginal moistening in females, as well as more variable heart rate, blood pressure, and breathing rate compared to stages 2 through 4. Additionally, exhibits intermittent features like facial twitches and eye movements, distinguishing it from non-REM (NREM) sleep stages
• Sleep


  A state that the brain actively produces, characterized by decreased response to stimuli
• Vegetative State


  Alternates between periods of sleep and moderate arousal, with no awareness of surroundings. Breathing is more regular, and a painful stimulus produces autonomic responses
• Polysomnograph


  A combination of EEG (electroencephalograph) and eye-movement record
• Paradoxical or REM Sleep


  • Characterized by high brain activity combined with muscle relaxation, representing a paradoxical state of deep and light sleep simultaneously
• Stage 2 Sleep


  • Sleep spindles and K-complexes. Sleep spindle consists of 12- to 14-Hz waves during a burst that lasts at least half a second. K-complex is a sharp wave associated with temporary inhibition of neuronal firing
• Minimally conscious state

  One stage higher than vegetative state, with occasional purposeful actions and limited speech comprehension. Can last for months or years
• In the United States, Nathaniel Kleitman and Eugene Aserinsky initially observed eye movements in sleeping individuals to gauge the depth of sleep, assuming eye movements ceased during sleep. Through meticulous measurements, they concluded these eye movements were inherent to sleep. They termed these periods Rapid Eye Movement (REM) Sleep. While REM sleep refers to humans, paradoxical sleep is preferred for non-human species due to the absence of eye movements in many
• Midbrain cut induces prolonged sleep, highlighting the midbrain's role beyond sensory relay. Even after severing sensory tracts, normal wake-sleep cycles persist, emphasizing the midbrain's significance in promoting wakefulness
• Stage 3 Sleep


  • Heart rate, breathing rate, and brain activity decrease, while slow, large-amplitude waves become more common
• Narcolepsy is a condition characterized by frequent periods of sleepiness during the day, with symptoms like attacks of sleepiness, cataplexy, sleep paralysis, and hypnagogic hallucinations
• Serotonin and norepinephrine

  Inhibit REM sleep
• Locus Coeruleus


  Located in the pons, fires bursts of impulses in response to significant events, releases norepinephrine widely throughout the cortex
• GABA


  The primary inhibitory neurotransmitter in the brain, allowing for variations in sleep across different brain regions
• REM sleep


  Rapid Eye Movement sleep, distinguishing it from non-REM (NREM) sleep stages
• Pontomesencephalon


  Part of the reticular formation, sustains cortical arousal by integrating sensory inputs and generating spontaneous activity
• Sleep Apnea is one type of insomnia, characterized by impaired ability to breathe while sleeping
• Acetylcholine stimulation


  Induces REM sleep
• Acetylcholine is released during wakefulness and REM sleep but not during slow-wave sleep
• Reticular Formation


  Contains neurons crucial for arousal regulation, with ascending axons implicated in this function
• PET Scans during REM sleep


  Study brain mechanisms on participants who were sleep-deprived and immobilized to ensure accurate imaging, characterized by distinctive PGO waves
• Insomnia is characterized by inadequate sleep, causes include noise, temperature, stress, pain, diet, medications, and underlying medical conditions such as epilepsy, Parkinson’s disease, and depression
• Sleepwalking, associated with additional sleep difficulties, occurs mostly in children during stage 3 or 4 sleep early in the night and not during REM sleep
• Periodic Limb Movement Disorder is characterized by repeated involuntary movement of the legs and sometimes the arms
• Clinico-Anatomical Hypothesis


  • Dreams begin with arousing stimuli generated within the brain combined with recent memories and sensory information
  • Dreams are thinking that takes place under unusual conditions
  • Brain areas are free to generate images without constraints or interference
  • Activity is suppressed in the prefrontal cortex, important for working memory
  • Sudden scene changes are common in dreams
• Sleep and Memory


  • Sleep improves memory
  • Memory often improves after learning something and then sleeping
  • Sleep enhances memory of some events more than others
  • Sleep helps people reanalyze their memories
  • Hippocampal activity during sleep correlates with improvement in performance
  • Weakening synapses during sleep emphasize the ones that were strengthened during wakefulness
• Sleep and Energy Conservation


  • Sleep's original function is to save energy
  • Sleep conserves energy during inefficient times
  • Body temperature decreases by 1º or 2º C during sleep, saving energy
  • Muscle activity decreases during sleep, saving more energy
  • Animals increase sleep duration during food shortages
• Activation-Synthesis Hypothesis


  • REM is a way of arousing a sleeper just enough to shake the eyes back and forth
  • During REM sleep, the motor cortex is inactive, and major postural muscles are virtually paralyzed
  • Dreams begin with arousing stimuli generated within the brain combined with recent memories and sensory information
• Sexsomnia, or sleep sex, is a condition where individuals engage in sexual behavior while asleep, either with a partner or through masturbation, and have no recollection of it afterward
• REM Behavior Disorder involves moving around vigorously during REM periods, apparently acting out dreams, often about defending themselves against attack
• Narcolepsy is a condition characterized by frequent periods of sleepiness during the day
• Functions of REM Sleep


  • REM stands for Rapid Eye Movement
  • About one-fifth of sleep is in REM
  • REM is characterized by high brain activity, vivid dreams, and rapid eye movement
  • Most dreaming occurs during REM
  • REM is important for memory storage, especially for weakening inappropriate connections
• Main symptoms of Narcolepsy


  • Gradual or sudden attacks of sleepiness during the day
  • Occasional cataplexy—an attack of muscle weakness while the person remains awake
  • Sleep paralysis—an inability to move while falling asleep or waking up
  • Hypnagogic hallucinations—dreamlike experiences that the person has trouble distinguishing from reality, often occurring at the onset of sleep
• Night terrors are experiences of intense anxiety from which a person awakens screaming in terror, occurring during NREM sleep and more common in children
• Functions of Sleep


  • Resting muscles
  • Decreasing metabolism
  • Rebuilding proteins in the brain
  • Reorganizing synapses
  • Strengthening memories
  • Inadequate sleep leads to trouble concentrating and vulnerability to illness, especially mental illness
• Coma


  An extended period of unconsciousness caused by head trauma, stroke, or disease. Low level of brain activity throughout the day, and little or no response to stimuli