Chapter 19: Sleep & Circadian Rhythms
which things happen during nonREM sleep
- EEG is high amplitude, low frequency - Eyes do not move - It is also known as slow wave sleep
When is the SCN most active? Least active? What is the significance of this? How could diurnal animals express opposite behavior and physiology from nocturnal animals, if the SCN is always active at the same time in both species?
- in all species, the SCN is more active during the day than during night
Describe 6 functions of sleep. Is any one function of sleep more important than another?
- restoration of energy - strengthens immune system - consolidation of memories - growth/development - creative thinking - protective function from predators
Why do we dream? Explain in terms of the three main theories (Freud, Memory consolidation hypothesis, and Activation synthesis theory)
1. freud's idea that we need to satisfy our wishes and discharge otherwise unacceptable feelings; dreams have meanings 2. memory consolidation hypothesis: memories of the day's event are sorted and filed away during REM sleep 3. activation synthesis theory: dreams are a physiological artifact of cyclic pons activity - activation: pons stimulates thalamus, which activates association cortex areas, evoking random memories - synthesis: frontal cortex tries to weave these images and emotions into a coherent story
How can circadian rhythms be measured? (Explain how behavioral and physiological rhythms might be measured). Give examples.
Human: Actiwatch Fruit Fly: Drosophila Activity Monitor Mouse: Running Wheel
Describe the typical sleep cycle for humans, in terms of NREM and REM. When is REM most prevalent? What happens physiologically during REM sleep?
NREM sleep constitutes about 75 to 80 percent of total time spent in sleep, and REM sleep constitutes the remaining 20 to 25 percent. The average length of the first NREM-REM sleep cycle is 70 to 100 minutes. The second, and later, cycles are longer lasting—approximately 90 to 120 minutes - Most REM sleep occurs during the second half of the night, with NREM sleep dominating the first half of the night. - Unlike wakefulness, REM sleep is characterized by dreaming, visual hallucinations, increased emotion, lack of self-reflection, and a lack of volitional control.
Why is REM sleep also called paradoxical sleep?
REM sleep is "paradoxical" because of its similarities to wakefulness. Although the body is paralyzed, the brain acts somewhat awake, with cerebral neurons firing with the same overall intensity as in wakefulness.
Which areas of the brain are more/less active during REM sleep?
The key brain structures responsible for producing REM sleep = are located in the brainstem -limbic system -hippocampus -amygdala
What is the significance of the retinohypothalamic tract?
The retinohypothalamic tract sends information to the suprachiasmatic nuclei regarding the amount of light in the external environment; the suprachiasmatic nuclei use this information to coordinate circadian rhythms with the solar day.
Differentiate between various stages of sleep, given specific types of waves, spindles or complexes. a. How does EEG change during the various states of NREM sleep? b. Which stage has the highest amplitude and lowest frequency? c. Which stage resembles a wake EEG?
There are five different stages of sleep including both REM (rapid eye movement) and NREM (non-rapid eye movement) sleep. The five stages make one sleep cycle which usually repeat every 90 to 110 minutes. Stage 1 non-REM sleep marks the transition from wakefulness to sleep. This stage typically lasts less than 10 minutes and is marked by a slowing of your heartbeat, breathing, and eye movements , as well as the relaxation of your muscles. Stage 2 non-REM sleep is a period of light sleep before you enter deeper sleep, lasts roughly 20 minutes. Stage two is characterized by further slowing of both the heartbeat and breathing, and the brain begins to produce bursts of rapid, rhythmic brain wave activity known as sleep spindles. Formerly known as stages 3 and 4, stage 3 (N3) is the final stage of non-REM sleep. This is the deepest period of sleep and lasts 20 to 40 minutes. Your heartbeat and breathing slow to their lowest levels, and your muscles are so relaxed that it may be hard to awaken you. REM sleep occurs 90 minutes after sleep onset, and is a much deeper sleep than any of the three stages of non-REM sleep. REM sleep is defined by rapid eye movements and an almost complete paralysis of the body, and a tendency to dream. a. - Typically, as one goes to sleep, the low-voltage fast EEG pattern of wakefulness gradually gives way to slower frequencies, as NREM sleep goes from stage N1 (decrease in alpha) to stage N2 (spindles, K-complexes) to stage N3 (increasing amplitude and regularity of delta rhythm) b. - Stage 3 and stage 4 of sleep are often referred to as deep sleep or slow-wave sleep because these stages are characterized by low frequency (up to 4 Hz), high amplitude delta waves ([link]). c. - Stage 5 Sleep (REM Sleep) of the Sleep Cycle
What do fetal SCN transplants do to arrhythmic animals? Why is this important?
Transplants containing fetal SCN have been shown to restore circadian behavior in SCN-lesioned arrhythmic animals
What have experiments shown about the effects of sleep deprivation? Why are so many humans sleep deprived?
effects of sleep loss: - fatigue - impaired concentration -> accidents - slowed performance -> accidents - irritability - suppression of immune system -> illness Sleep deprivation is a crisis in society - most people are moderately to severely sleep deprived. 71% do not meet the recommended 8 hours/night - middle-schoolers, high-schoolers, college students are especially vulnerable, along with elderly adults - 75% of people experience sleep problems each week (ALARMING)
Circadian rhythms - Give specific examples of behavioral and physiological circadian rhythms in humans. Again, explain their importance.
ex: the sleep-wake cycle, the body-temperature cycle, and the cycles in which a number of hormones are secreted. The menstrual cycle in women and the hibernation cycle in bears are two good examples.
What did the isolation experiments in humans teach us about free-running?
free-running: still have a rhythm just not entrained (not entrained to any zeitgebers) Research Q: Do humans have an internal biological clock? To investigate the nature of biological rhythms, experimenters have enticed subjected to spend up to 6 months in underground environments totally cut off from external cues - evidence of rhythm - wake up 1 hr later (25 hour clock - lose time) - upset at the end because they lost a day
How can we measure sleep objectively and scientifically?
hard to define* "the natural periodic suspension of consciousness during which the powers of the body are restored" - a state of torpid inactivity - DEATH - the closing of leaves or petals at night "a natural periodic state of rest for the mind and body, in which the eyes usually close and consciousness is completely or partially lost, so that there is a decrease in bodily movement and responsiveness to external stimuli
Describe the anatomy of the suprachiasmatic nucleus. Where is it located? What is the significance of its location in the brain?
hypothalamic structure location: just dorsal to the optic chiasm
which of the following is TRUE about REM sleep
it is also known as paradoxical sleep
which of the following is a zeitgeber?
light-dark cycle (most promenent zeitgeber to entrain us)
What happens to behavior and physiology when the suprachiasmatic nucleus (SCN) is lesioned? How does this differ from those that are placed in constant conditions (or in an isolation experiment, where subjects control their own lighting)?
no rhythms at all - light influences, or entrains, the SCN via retinohypothalamic tract (RHT) directly via specialized retinal ganglion cells the contain melanopsin, a recently discovered photopigment - fetal SCN transplants can restore rhythms - the SCN modulates hypothalamic function (sends signals to so many areas in brain [variety of functions]) - Jet lag is caused by a mismatch between our internal clock (SCN) and the new light-dark cycle
What evidence is there that we have an endogenous clock?
raitonale: if subjects display rhythms after all external cues (zeitgebers) are removed, then the clock must be inside the subject's body or brain
Describe how sleep patterns change with age. Be specific about how REM sleep, NREM sleep, and wakefulness change over development. Are circadian rhythms present at birth in humans? Why or why not? What evidence do we have?
sleep patterns change dramatically with age (more rhythm, takes time to adjust to light/dark cycle) over development -> consolidation of patterns babies: 50% of total sleep time in REM 16/24 hours asleep - infants' sleep patterns are fragmented, until, the suprachiasmatic nucleus, the mind's clock, develops - adolescents are chronically sleep deprived (has to do with surge of emotions)? what can we do to fix the problem? school start times too early!
Biological rhythms - Describe examples of biological daily rhythms in your body and their importance. - Differentiate between ultradian, circadian, and circannual rhythms. Give examples. - How do external and internal factors influence biological rhythms? Give examples.
sleeping and waking, hibernation, breathing, walking, menstrual cycle, body, temperature, hormonal release - ultradian rhythms (many times per day, eating/drinking), circadian rhythms (about once a day, body temperature), circannual (depression in winter) rhythms - rhythms are influenced by multiple factors \\ external factors: light/dark cycle, alarm clock, deadlines \\ internal factors: hormonal release, SCN (master clock)
How does the SCN modulate behavior and physiology? To what brain areas do the SCN project? What sorts of physiological and behavioral rhythms does it modulate?
the principal circadian pacemaker in the mammalian brain and, as such, it generates circadian rhythms in rest and activity, core body temperature, neuroendocrine function, autonomic function, memory and psychomotor performance
Describe the difference between zeitgeber, entrainment, free-running, and arrhythmia.
zeitgeber: a time-giver, something that allows an individual to have their rhythms entrained. allow for entrainment to happen entrainment: you're capable of waking up at the same time every single day, very regulated rhythm. well-timed to external cues (zeitgebers), behavior is coordinated well free-running: still have a rhythm just not entrained (not entrained to any zeitgebers) arrhythmia: no rhythm, if an individual's SCN was damaged or lesioned
