lecture 8: what is sleep Flashcards
circadian rhythm
the physical, mental and behavioural changes an organism experiences over a 24hr cycle
cira = about
dian = day
wake maintenance zone
feeling more alert just before the period where you are feeling sleepy (6-9pm)
- this was advantageous many yrs ago, as if they were alert just before dark they could find shelter/warmth
melatonin
a natural chemical which is being modulated across the sleep/wake cycle
- it peaks in the middle of the night
free-running sleep-wake cycle
occurs when an individual’s circadian rhythm drifts later each day, resulting in a sleep schedule that is not synchronized with the 24-hour day
suprachiasmatic nucleus of the hympthalamus (SCN)
- a small region in the hypothalamus that acts as the body’s central circadian pacemaker, regulating sleep-wake cycles and coordinating various biological rhythms with the 24-hour day-night cycle
- this is where our internal clock is located
- this location is vital, if it is damaged it impairs the sleep wake cycle
pineal gland
releases hormone melatonin at night
zeitgeber
- any external or environmental cue which acts as a cue in the regulation of the bodys circadian rhythms
- light is the primary zeitgeber (time giver)
how do melanosopin receptors work
- melanosopin receptors in the eye respond to the presence of light by transmitting signals to the SCN
- light induced activation of the SCN prevents the pineal gland from producing melatonin, a hormone that otherwise signals “biological night”
- light dark entrainment of the SCN synchronises ‘peripheral oscillators’ throughout the body, although these can subsequently be shifted by factors such as eating, exercise and body temp
phase delay
- wake up later
- a phase delay means your internal clock shifts to later times
phase advance
- wake earlier
- phase advance means it shifts to earlier times
inactivity theory
sleep at night = less likely to be eaten and most likely to have offspring, conserve energy
limitation = sleep forces us to remain quiet during periods of vulnerability
- it is always safer to remain conscious in order to be able to react to an emergency. thus there does not seem to be any advantage of being unconcious and asleep if safety is paramount
energy conservation theory
- sleep forces us to conserve energy at times when we would be relatively inefficient at searching for food
- energy metabolism is reduced by 10% during sleep in humans, decreased body temp and caloric demand
recuperation/repair explanations of sleep
a. sleep deprivation should produce physiological and psychological disturbances
b. these disturbances should get worse as deprivation continues
c. after deprivation much of the sleep debt will be recovered
- sleep is crucial for the body and brain to rest, repair, and restore physiological functions, including muscle repair, tissue growth, and hormone release
peter tripp and randy gardener
peter tripp (1959) = 201 hours (98 days)
- psychosis
Randy Gardner (1964) = 264 hrs (11 days)
- moodiness, problems with concentration and short term memory, paranoia and hallucinations
- only 6 hrs of extra sleep during the following week
what was the impact of sleep deprivation on animal studies
after 2 weeks unable to thermoregulate, lost weight, infections
after 4 weeks = death
what beneficial things happen during sleep
muscle growth, tissue repair, protein synthesis and growth hormone release occur mostly during sleep
what are the impacts of poor sleep
- sleep disruption eg: shift work is linked to cancer, diabetes, cardiovascular risks, obesity, mood disorders and age related macular degeneration
- poor sleep is linked to several psychiatric disorders and Alzheimer’s disease
glymphatic system involvement
- slow waves of neural activity, as occur during sleep, are associated with changes in vasodilation in the brain
- these changes are thought to pump cerebrospinal fluid (CSF) around the brain
- the CSF interacts with interstitial (extracellular) fluid and picks up the waste products of metabolism so that they can be transported out of the brain via the glymphatic system
glymphatic system = a waste clearance pathway in the brain