mod 5

• Circadian rhythms


  Biological processes that occur regularly on approximately a 24-hour cycle
• Several other bodily functions, such as body temperature, hormone production, and blood pressure, also follow circadian rhythms
• Purpose of the circadian rhythm

  • To keep our internal workings in phase with the outside world
• Human circadian clock generates a rhythm slightly longer than 24 hours when it has no external cue to set it
• Circadian rhythms remain consistent despite lack of environmental cues indicating the time of day
• Mechanisms of the circadian rhythms

  • The Suprachiasmatic nucleus
  • Genes that produce certain proteins
  • Melatonin levels
• Suprachiasmatic nucleus (SCN)


  Part of the hypothalamus and the main control center of the circadian rhythms of sleep and temperature
• Damage to the SCN results in less consistent body rhythms that are no longer synchronized to environmental patterns of light and dark
• The SCN generates circadian rhythms in a genetically controlled, unlearned manner
• Single cell extracted from the SCN and raised in tissue culture continues to produce action potential in a rhythmic pattern
• Various cells communicate with each other to sharpen the circadian rhythm
• Two types of genes responsible for generating the circadian rhythm

  • Period - produce proteins called Per
  • Timeless - produce proteins called Tim
• Per and Tim proteins increase the activity of certain kinds of neurons in the SCN that regulate sleep and waking
• Mutations in the Per gene result in odd circadian rhythms
• Melatonin


  A hormone that increases sleepiness
• Melatonin secretion usually begins 2 to 3 hours before bedtime
• Melatonin feeds back to reset the biological clock through its effects on receptors in the SCN
• Melatonin taken in the afternoon can phase-advance the internal clock and can be used as a sleep aid
• Electroencephalograph (EEG)


  Allowed researchers to discover that there are various stages of sleep
• A polysomnograph is a combination of EEG and eye-movement records
• Stage 1 sleep


  Sleep has just begun, alpha waves are present, brain activity begins to decline
• Stage 2 sleep


  Characterized by sleep spindles and K-complexes
• Stage 3 and Stage 4 sleep

  Constitute slow wave sleep (SWS), characterized by slow, large amplitude EEG waves, slowing of heart rate, breathing rate, and brain activity, highly synchronized neuronal activity
• Rapid eye movement sleep (REM)


  Periods characterized by rapid eye movements during sleep, EEG waves are irregular, low-voltage and fast, postural muscles of the body are more relaxed than other stages
• Stages other than REM are referred to as non-REM sleep (NREM)
• Sleep cycle


  Progress through stages 1, 2, 3, and 4 in sequential order, then cycle back through the stages from stage 4 to stages 3 and 2 and then REM, sequence repeats with each cycle lasting approximately 90 minutes
• Stage 3 and 4 sleep predominate early in the night, the length of stages 3 and 4 decrease as the night progresses
• REM sleep is predominant later in the night, the length of the REM stages increases as the night progresses
• REM is strongly associated with dreaming, but people also report dreaming in other stages of sleep
• Physiological processes in NREM vs REM sleep

  • Brain activity, Heart rate, Blood pressure, Sympathetic nerve activity, Muscle tone, Blood flow to brain, Respiration, Airway resistance, Body temperature, Sexual arousal
• Basal forebrain


  An area anterior and dorsal to the hypothalamus containing cells that extend throughout the thalamus and cerebral cortex, cells release the inhibitory neurotransmitter GABA which is essential for sleep
• Hypothalamus


  Contains neurons that release "histamine" to produce widespread excitatory effects throughout the brain, anti-histamines produce sleepiness
• Orexin


  A peptide neurotransmitter released in a pathway from the lateral nucleus of the hypothalamus highly responsible for the ability to stay awake
• Orexin


  Stimulates acetylcholine-releasing cells in the basal forebrain to stimulate neurons responsible for wakefulness and arousal
• Reticular formation


  A part of the midbrain that extends from the medulla to the forebrain and is responsible for arousal
• Pontomesencephalon


  A part of the midbrain that contributes to cortical arousal, axons extend to the thalamus and basal forebrain which release acetylcholine and glutamate to produce excitatory effects to widespread areas of the cortex
• Locus coeruleus


  A small structure in the pons whose axons release norepinephrine to arouse various areas of the cortex and increase wakefulness, usually dormant while asleep
• Brain mechanisms associated with wakefulness and arousal

  • Pontomesencephalon (acetylcholine, glutamate)
  • Locus coeruleus (norepinephrine)
  • Basal forebrain (excitatory cells - acetylcholine, inhibitory cells - GABA)
  • Hypothalamus (histamine, orexin)
• Insomnia


  Caused by lack of hypothalamic cells that produce and release orexin, primary treatment is with stimulant drugs which increase wakefulness by enhancing dopamine and norepinephrine activity
• Insomnia can also be caused by a number of factors including noise, stress, pain medication, disorders such as epilepsy, Parkinson's disease, depression, anxiety or other psychiatric conditions, and dependence on sleeping pills and shifts in the circadian rhythms