Lecture 10 Flashcards
Do all multicellular organisms sleep
Yes - so this is shared by many creatures on the planet
How does sleep work?
Animals have rhythms that correspond to the functional activity of the animal
What is the biological clock
Animals have an internal mechanism that spontaneously generates a rhythm.
Define Endogenous circadian rhythms
Internally controlled cycles that last about a day
How do we know our biological clock (rhythm) is internally generated
If you stay up all night, you feel sleepier as it gets later but then perk up in the morning. Animals kept in total darkness still keep to a 24 hour cycle (DeCoursey, 1960). Humans kept in an environment with a 28 hour cycle cannot synchronise - they slip back to a 24 hour cycle. Blind and deaf animals generate nearly normal circadian rhythms. Circadian rhythms are maintained despite most types of brain damage, anaesthesia, and food deprivation.
What generates this sleeping rhythm
The biological clock
What is the biological clock
A mechanism in our brain that generates the sleeping cycle.
Where is the biological clock
Suprachiasmatic nucleus (SCN). Which is part of the hypothalamus, above the optic chiasm
What happens when the suprachiasmatic nucleus is damaged
It causes damage to the circadian rhythms
How do we know the suprachiasmatic nucleus generates a rhythm automatically
Remove the SCN and keep it is a tissue culture - it continues to prodce a 24 hour rhythm of action potentials. Hamsters with a mutant gene coding a 20 hour rhythm, SCN removed and implanted in normal hamsters, they start to live a 20 hour cycle.
How does the biological clock work
Controls the pineal gland = an endocrine glad posterior the thalamus. Releases melatonin - Hormone that makes us sleepy
What happens when yo upset the biological clock
The clock is internal, but it still responds to the environment. Feedback system between our clock and the world to allow us to adapt to change. So although circadian rhythms can exist without light, light is crucial for periodically resetting them. The stimulus that changes the clock is called zeitgeber. Good for changes in seasons, activity levels; after a weekend of late drinking and late morning 8 am Monday feels like 5 am.
What is zeitgeber
Time-giver: for most land mammals the dominant zeitgeber is light, but we also respond to exercise, noise, temperature and meals. Some marine mammals respond to tides. People in Scandinavian countries become insomniac during the winter - where there’s only 2 hours of sunlight a day. Hamsters living in constant light have no coordination and two sleep and two wake cycles when the SCN in one hemispheres is out of the phase with the right
How does jet lag implicate the biological clock
Disrupting rhythms by crossing time zones. Sleeping at the wrong times = depression, lack of concentrations and nausea. Mismatch between biological clock and external stimuli - we are not adapted to moving so fast. Can be stressful and raise cortisol levels - damaging in the long term! Delaying your sleep is easier than having to sleep earlier. Travelling east to west is easier - you just stay up later, but west to east is hard and your night has been shortened, so you need to catch up in the following days
How does shift work impact the biological clock
Even years after working shifts people can have disruptive sleep patterns and feel fatigued, can’t sleep well during the day, don’t adjust when working at night, as well as the light levels aren’t high enough in artificial conditions - need to have complete reversal to fully change that biological clock
Why is light so important to the biological clock
Optic chiasm and suprachiasmatic nucleus are close to eachother. Small branch of the optic nerve goes directly from the retina to the SCN and not the visual cortex. Input to this pathway comes from special type of retinal ganglion cells - special photopigment, melanopsin, responds directly to light with no input from rods and cones, respond slowly and turn off slowly, so the SCN gets an idea of general light intensity - perfect to gauge the time of the day
Can a blind mole rat respond to light
YES
How many stages of sleep are there and what to they do
- Stage 1 and 2 = irregular activity, high but declining, bursts of activity in stage 2, cortex still receiving sensory input. Stage 3 and 4 = slow wave sleep = neuronal activity is highly synchronised, sensory input is reduced
How can we detect different stages of sleep
With EEG’s, can be used to detect electrical signals of spontaneous brain activity OR in response to a stimuli
In addition to the 4 stages what other stage is there
REM sleep - Rapid Eye Movement sleep - also called paradoxical sleep. Neither light nor deep sleep - light because lots of brain activity but deep because muscles are relaxed
What does REM stand for and what does it mean
Rapid Eye Movement, where you are in neither a light sleep or deep sleep because there is lots of brain activity going on but muscles are relaxed
What is the brain doing during REM sleep
Lateral geniculate nucleus in the thalamus - limbic system - emotion. Pons = bridge, axons from cortex cross here to spinal cord - for movement. PGO waves (pons-geniculate-occipital)
What happens when you lesion the pons
In cats, they still have REM sleep but muscles are not relaxed - chases prey, jumps and pounces
Name 4 sleep disorders and what they are
Insomnia: Stress, anxiety, depression, shifting circadian rhythms and dependent on sleeping pills. Sleep Apnea: Inability to breathe while sleeping - obesity/old age? Narcolepsy: Attacks of sleepiness during the day, REM during the day? Periodic Limb Movement Disorder: Involuntary movement of the legs/arms, maybe something to do with the pons?
