PSYCH 261- Circadian Rythms & Sleep

Biological Rhythms

• endogenous biological clocks (internal influences on rhythms, ie. chronotypes)

• exogenous changes in environment (external influences, ie day and night)

Cortisol and sleep

• stress hormone

  • peaks when you wake up

  • makes you alert for the day

  • lowest at bedtime

Melatonin and sleep

• hormone produced by the pinneal gland, promotes sleep

  • peaks right before sleep, continues through night

  • lowest when waking up

Temperature and sleep

• body temp is highest when awake

  • body temp lowest right before sleep

  • this is why a cold room promotes sleep

Chronotypes

• Early chronotypes (early birds, kids and older adults)

• Late chronotypes (night owls, adolescents and 20-year-olds)

why are late school start times better?

• b/c they align with adolescent late chronotypes

Zeitgebers

• factors that function to reset our circadian clocks

  • light

  • exercise

  • mealtimes

  • temperature

Free Running rhythms

• when we don’t have natural light exposure, shifts our clocks (CIRCADIAN DRIFT)

• sleep later, wake later

• b/c our clocks don’t reset w light

How long do our circadian clocks run?

just over 24 hours (ie. 24.3 or 24.5)

Blind people with free-running rhythms

• experience circadian drift

• causes them to be out-of-sync with society

Eastward travel

• need to PHASE ADVANCE the circadian system

  • need to fall asleep earlier, which is harder

Westward travel

• need to PHASE DELAY the circadian system

  • stay up for a few more hours, which is easier (b/c our system runs in cycles over 24hrs)

What is the best habit for the sleep system?

• to have regular wake-up times

The Superchiasmatic Nucleus (SCN)

• controls Circadian rhythms, does not depend on other structures for help

• it is the “clock” keeping time within our brain

• above the optic chiasm

Intrinsically Photosensitive Retinal Ganglion cells (ipRGCs)

• contain MELOPSIN

• respond directly to light, don’t need help from photoreceptors

• travel through the RETINOHYPOTHALAMIC TRACT

Non-image forming ipRGCs

• send light info (axons) directly to SCN

why is light before bed harmful?

• causes the ipRGCs to recieve light signals that they confuse with sunlight

• light to serve as a zeitgeber, throws off circadian rhythms

Third visual pathway

• retinalhypothalamic tract

• terminates in the superchiasmatic nucleus

How is the sun a zeitgeiber?

The Suprachiasmatic Nucleus feedback system

• per and tim genes

• transcribed into MRNA

• turned into protiens (lagged)

• sun recieved by ganglion cells

• breaks down the tim protiens

• resets the cycle

When is per and tim MRNA the highest

sunset/night

when are per and tim proteins the highest

right before sunrise

What is one good thing to do to better your sleep?

• get exposed to bright light IMMEDIATELY in the morning

  • reset your circadian rythyms in the morning, breaking down the tim protiens and resetting the feedback loop

  • lounging in the dark makes it harder to sleep

How does melatonin secrete?

• feedback system:

  • SCN

  • Paraventricular Nucleus

  • intermediolateral nucleus of the spinal cord

  • superior cervical ganglion

  • pineal gland

What secretes melatonin?

• the pineal gland, 2-3 hours before bed

  • enters the bloodstream

  • effects the SCN through MT1 and MT2 receptor

What are the arousal Nuclei?

• PPT (pedunculopontine nuclei)

• LDT (laterodorsal tegmental nuclei)

• LC (locus coeruleus)

• Raphe (dorsal and medial raphe nuclei)

• TMN (Tuberomammillary nucleus of hypothalamus)

• LH (lateral hypothalamus)

• vPAG (ventral periaqueductal Grey)

• BF (Basal Forebrain)

What is the inhibitory nucleus?

VLPO

the ventrolateral preoptic nucleus

• release galanin and GABA

The Flip Flop switch: general principle

• when VLPO (inhibitory) is active, you would be asleep

• when LC, Raphe, TMN (arousal) is active, you feel awake

• flip flop switch is why sleep feels instantaneous

SCN and the flip-flop switch

• DAYTIME: SCN sends signals to:

  • INHIBIT vlpo

  • EXCITE LC, raphe, and TMN

• NIGHT:

  • stops sending signals so that inhibition takes over

Flip-flop switch: sleep pressure

• ADENOSINE: builds up throughout the day

  • disinhibits VLPO indirectly by INHIBITING excitatory areas

  • turns into ATP as we sleep, gets us ready for the next day

Sleep stages:

• alpha waves are relax and awake

• sleep stage 1: irregular and jagged waves, activity declines

• Stage 2: sleep spindles (bursts of waves), K-complexes (sharp, high amplitude)

• Stage 3 and 4: Slow wave sleep, getting synchrony in neurons

• REM sleep: paradoxical sleep, eyes move, body paralyzed, increased activity/light sleep

Polysomnograph

• EEG waves and eye movement hroughout the night

Hypnogram

• time spent in various sleep cycles

characteristics of hypnograms

• sleep cycles repeat every 90 mins

• deep sleep early, rem sleep late

Sleep in old v young people

• old people wake up more, less deep sleep and rem

• young ppl more deep sleep and rem

functions of sleep

• restoration (growth hormones and cell regen)

• clearance (fluid moves and system flushes)

• Memory cosolidatees

Activation Synthesis model of dreaming

• areas are activated without stimuli, which is why dreaming is so bizzare

Lucid dreaming

• showing a mix of awake waves and rem waves, irregular

narcolepsy symptoms

• sleep attacks (loss of orexin in the hypothalamus)

• cataplexy

• sleep paralysis

• hallucinations

sleep apnea (OSAS)

not getting enough air

• stop breathing

• wake up and gasp

• cpap

Parasomnias

non rem:

• confusion arousal

• sleep terrors

• somnambulism (sleep but doing things)

REM":

• rem behaviour disorder

Insomnia

• onset insomnia (can’t get to sleep)

• Maintenance insomnia (cant stay asleep)

triggers of insomnia

• stress

• too much light at bedtime (blue light is what the ganglion cells are most affected by)

• high temp at bedtime

• late night exercise and eating

• drugs (caffeine and alcohol)

• irregular bedtimes

• late night media use