biopsych: Wakefulness and Sleep

• Endogenous rhythms


  Internal rhythms that last about a day (e.g., wakefulness and sleepiness)
• Circadian rhythm


  • Self-generated duration of about 24 hours
  • Affects mood, body temperature, eating, drinking, urination, hormone secretion, sensitivity to drugs, and other variables
• Zeitgeber


  Stimulus that is necessary for resetting the circadian rhythm
• Jet lag


  Disruption of biological rhythms due to crossing time zones
• Phase-delay


  What happens to circadian rhythms when travelling west - staying awake late and awakening partly adjusted to new schedule
• Phase-advance


  What happens to circadian rhythms when travelling east - sleeping and awakening earlier than usual
• Repeated adjustments of circadian rhythm can increase cortisol levels, which can damage the hippocampus and cause memory loss
• Night shift workers


  Often have difficulty adjusting to wake/sleep cycle, feel groggy, don't sleep well during the day, body temperature peaks when sleeping instead of working
• Larks and owls


  People with natural circadian rhythms that predispose them to be early risers or evening people
• Suprachiasmatic Nucleus (SCN)


  Nucleus in hypothalamus that controls sleep and temperature rhythms, generates circadian impulses
• Genetic mutation in hamsters causes SCN to generate 20-hour circadian rhythm, which persists when transplanted to other hamsters
• Retinohypothalamic path


  Extends from retina to SCN, resets SCN
• Melanopsin-containing retinal ganglion cells


  Respond to slow changes in overall light duration, allow blind people to entrain to sunlight patterns
• Period (per) and timeless (tim) genes

  Regulate circadian rhythms in flies by coding for PER and TIM proteins, which inhibit their own production
• Melatonin


  Hormone released by pineal gland, increases sleepiness, stimulates receptors in SCN to reset biological clock
• Sleep


  Brain-produced state characterized by decreased response to stimuli
• Interruptions of consciousness


  • Sleep
  • Coma
  • Vegetative state
  • Minimally conscious state
  • Brain death
• Electroencephalograph (EEG)


  • Records gross electrical potentials in brain through scalp electrodes
• Polysomnograph


  • Combination of EEG and eye-movement records
• Alpha waves


  Frequency of 8-12 Hz, typical of relaxed consciousness
• Stage 1 sleep


  Light sleep with irregular, jagged, low-voltage brain waves
• Stage 2 sleep


  Characterized by sleep spindles and K-complexes
• Stages 3 and 4 (slow-wave sleep)


  Characterized by slow, large-amplitude brain waves
• Paradoxical/REM sleep


  Brain is very active but muscles are completely relaxed, associated with dreaming
• Non-REM (NREM) sleep


  Stages of sleep other than REM
• Sleep cycle


  Stage 1 -> Stage 2 -> Stages 3 and 4 -> REM, repeating in 90-minute cycles
• Early in the night, stages 3 and 4 predominate, but toward morning, stage 4 grows shorter and REM grows longer
• Reticular formation


  • Structure extending from medulla to forebrain, lesions decrease arousal
• Pontomesencephalon


  • Part of reticular formation that contributes to cortical arousal, stimulation can awaken or increase alertness
• Locus coeruleus


  • Structure in pons that emits norepinephrine impulses in response to meaningful events, important for storing information, usually silent during sleep
• Hypothalamus


  • Stimulates arousal by releasing histamine, which has excitatory effects, antihistamines cause drowsiness
• Lateral nucleus of hypothalamus

  • Releases peptide orexin, which promotes wakefulness
• Reticular formation


  • A structure that extends from the medulla into the forebrain
  • Lesions through the reticular formation decrease arousal
• Pontomesencephalon


  • A part of the reticular formation that contributes to cortical arousal
  • Stimulation of the pontomesencephalon awakens a sleeping individual or increases alertness in someone already awake
• Locus coeruleus


  • A structure in the pons that is inactive at most times but emits impulses, releasing norepinephrine, in response to meaningful events
  • The locus coeruleus is also important for storing information
  • The locus coeruleus is usually silent during sleep
• Hypothalamus

  • Certain areas stimulate arousal by releasing the neurotransmitter histamine, which produces excitatory effects throughout the brain
  • Antihistamine drugs produce drowsiness if they cross the blood-brain barrier
• Hypothalamus


  • A different group of axons release the peptide neurotransmitter orexin (also called hypocretin)
  • Orexin is necessary for staying awake
• Basal forebrain


  • Some of the axons release GABA and are essential for sleep
  • These neurons receive input from the anterior and preoptic areas of the hypothalamus
  • Another set of axons release acetylcholine
• During sleep, body temperature and metabolic rate decrease slightly
• Sleep


  • Depends on GABA-mediated inhibition
  • While spontaneously active neurons continue to fire at a normal rate, we are unconscious because GABA inhibits synaptic activity