Biological rhythms- sleep

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  • Biological Rhythms: Sleep
    • Biological Rhythms: Regular changes in behaviour & internal states of living organisms
      • Ultradian: Faster than 1 day- sleep cycles, eating behaviuor
      • Circadian: Takes 1day- sleep/wake cycle, hormone production
      • Infradian: Slower than 1 day- hibernation cycle, menstrual cycle
    • Sleep and wakefulness
      • Traditional view: sleep is passive default stage (NOT ACTUALLY TRUE). Brain needs stimulation from the environment to wake up- without stimulation it remains asleep
        • Cycles are controlled by two factors: 1- internally gene-related endogenous biological clocks. 2- External cues zeitgeber which resets biological clocks (day/night)
      • Experimental evidence- Bremer (1930) transected cats brains
        • Cutting between medulla & brainstem (encephale isole)--> normal sleep/wake cycle
        • Cutting at midbrain (cerveau isole)- constant deep sleep
      • Reticulo-thalamic system wakes up the brain
        • Ascending, Reticular, Activating, System (ARAS). This begins in the medulla and is a pathway to all the forebrain
      • Several biological systems co-vary with the sleep/wake cycle
        • Alertness (decreases during sleep)
        • Body temperature (decreases during sleep)
        • Growth Hormones (increase during sleep)
        • Cortisol, stress hormone (decreases during sleep)
          • Cortisol is released by: Hypothalamus-CRH-pituitary ACTH- adrenal gland=cortisol
          • Cortisol is released in response to stress and low blood sugar levels.
            • Cortisol increases blood pressure and inhibits CRH (negative feedback loop). in mins/hours
          • Gluconeogenesis- sugar new making. Sugar from scratch (from fatty acids not glycogen)
    • Supra-Chiasmatic Nucleus
      • SCN is the master pacemaker of the nervous system
        • SCN generates circadian rhythms. SCN cells show circadian firing patterns. Activity stimulates pineal gland which produced melatonin which promotes sleep
        • Firing patters of SCN remain circadian but not entrained (might be slightly longer than 24h)- even without zeitgeber and in preparation outside the body (in petri dish)
      • Lesions to the SCN or age related neuron loss disrupt circadian rhythms
      • Nucleus of the anterior (front) region of the hypothalamus (situated directly above the optic chiasm)
      • Input: connected to the retinae (retino-hypothalamic tracts). Sensitive to light
        • Output: signals to pineal gland
      • Retinal input signals light v dark: Light/dark cycle resets the biological clock 'zeitgeber'
        • Blind people without light perception show abnomal circadian rhythms (nothing to reset circadian rhythm. Treatment of blind (light-insensitive) people with oral administration of melatonin. Help train body to sleep
    • What distinguishes sleep from wakefulness? Hypothesis- the sleeping brain is less active than the wakeful brain. Test: measure brain activity during sleep and wakefulness
      • Measuring metabolic activity- more active neurons need more glucose & oxygen. Their levels are an index of how much activity is going on. Can localise the O2/glucose to know where the higher/lower activity is going on
        • fMRI: functional magnetic resonance imaging- measure oxygen levels through the different magnetic properties of O2 rich and O2 poor blood
          • Positron emission tomography (PET): measures glucose levels using radioactive glucose as a 'tracer'
        • During sleep: There is a reduced metabolic activity and reduced electrical activity. Except for REM sleep- Electical & metabolic brain activity almost like waking state. most vivid dreaming. same metabolic demands as awake
      • Measuring electrical activity- neurons that are active-exchange electrical signals. cant measure a single neuron because it is too small, so measure a group consisting of parallel aligned neurons that move in the same direction. Their AP are synchronised and fire at the same time
        • Electroencephalogram (EEG): place electrodes on the scalp, distant from neurons and it measures the firing groups of neurons
          • Theta- large persistent groups: synchronised EEG: Less active brain
          • Beta- small rapid changing groups: desynchronised EEG activity: Highly active
    • Sleep is a multi-stage process
      • Sleep stages are characterized by specific electrical brain activity in combination with specific muscle activity
        • Through the stages of sleep EEG synchronise, heart rate slows don, little eye movement, little muscle activity. Except in REM: EEG desynchronised, No muscle activity, rapid eye movement, heart rate speeds up (paradoxical sleep) Dreaming
      • Paradoxical sleep- dreaming: REM sleep: body held in paralysis, brain activity resembles waking state, vivid dreaming
        • Dream content is often negative- helplessness, falling, running without moving, threat. Psychoanalysis interpretation:subconscious mind is a battle ground, we want something forbidden so we hide it from selves and punish us from wanting it. Psychbiological interpretation- subconcious mind percives the body as immobilised and helpless which we are
      • Sleep is multi-stage process: during sleep, REM and non REM alternate. Time spent in each phase changes systematically. More time in deep sleep SWS in 1st half of the night, more time spent in REM/light sleep in 2nd half of the night
    • Multiple systems regulate sleep and wakefulness
      • Network involved in sleep & wakefulness: Basal forebrain, thalamic nuclei, hypothalamic nuclei, brainstem nuclei
      • Wakefulness: ARAS (through the thalamus), basal forebrain (kicks you awake), locus coeruleus- promotes wakefulness, produces noradrenalin for stress response (none during sleep)
        • Non-REM (light & SWS): basal forebrain (most neurons here are involved in increased alertness) but some trigger SWS. stimulating can induce SWS, lesion can prevent SWS. Raphe nuclei (in brainstem) produce seretonin and promote non rem. these nuclei have to become active. not passive state
          • REM sleep: Pontine nuclei (in pons)- control REM, stimulation triggers REM, lesion, revents REM sleep. lesion of nearby nucle prevent paralysis- sleep walking/acting out dreams. Produce Acetylcholine during rem/enhanced levels. activates the brain (used in learning)
            • The dreaming brain: similarities of REM sleep and schizophrenia- is Sz a form of waking dream state. Lack of prefrontal activity. Areas + correlated with REM-pons, amygdala, thalamus, parietal operculum, ACC. Areas - correlated, less active in REM- prefontal cortex, posterior parietal corex (bring together sensory info)
  • During sleep: There is a reduced metabolic activity and reduced electrical activity. Except for REM sleep- Electical & metabolic brain activity almost like waking state. most vivid dreaming. same metabolic demands as awake
  • Life-span changes of sleep patterns
    • Babies have more REM-as they get older REM decreases and becomes constant. Decrease in SWS. Sleep-wake cycle as a newborn is extended over many hours, interrupted. As they get older the cycles becomes longer and uninterrupted. The elderly have severely disrupted cycles and loose REM. interfers with growth and repair
  • Sleep deprivation: prolonged sleep deprivation is fatal. initial decrease in body temperature, metabolism, apetite= saving energy (pre hypernation)
    • Subsequently: failure of the immune system, loss of resistence to infection, death. Caveat: this might be due to the stress of being kept awake not due to lack of sleep. stress causes similar problems
      • How important is sleep?
        • Life-span changes of sleep patterns
          • Babies have more REM-as they get older REM decreases and becomes constant. Decrease in SWS. Sleep-wake cycle as a newborn is extended over many hours, interrupted. As they get older the cycles becomes longer and uninterrupted. The elderly have severely disrupted cycles and loose REM. interfers with growth and repair
        • Sleep deprivation in humans: impaired physical and cognitive functions: impaired speech, impaired memory, hallucinations, brain not functioning properly, cannot test if it would result in death
          • After sleep, the body will try to 'catch up' on missed sleep. it is selective. if you miss REM, it will alter the next nights sleep to include more REM. REM rebound.
          • Large inter-indiviual variety: most epople need approx 8h of sleep, some function on average of 4 or less
    • How important is sleep?
      • Sleep deprivation in humans: impaired physical and cognitive functions: impaired speech, impaired memory, hallucinations, brain not functioning properly, cannot test if it would result in death
        • After sleep, the body will try to 'catch up' on missed sleep. it is selective. if you miss REM, it will alter the next nights sleep to include more REM. REM rebound.
        • Large inter-indiviual variety: most epople need approx 8h of sleep, some function on average of 4 or less
  • Evolutionary perspective: The paradox of sleep: sleep is dangerous (leaves animal vulnerable unable to move and detect danger). All animals with brains show some form of sleep. In higher animals, sleep is controlled by a complicated system of interacting neurendocrine functions. NOT passive
    • Some animals have developed a method to stay awake while sleeping. there must be some evolutionary advantage but we havent worked it out yet. Dolphins- one half of hemisphere sleeps, the other is awake. to prevent drowning.

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