4.1 biological rhythms/sleep

biological rhythms

regular fluctuations in any living process

circadian vs ultradian vs infradian rhythms

circadian: ~24 hours (sleep/hormone cycles)

ultradian: <24 hours (sleep cycles/feeding)

infradian: >24 hours (menstrual cycle)

diurnal vs nocturnal

diurnal: active during day (humans)

nocturnal: active at night (most mammals)

SCN

suprachiasmatic nucleus 

located in hypothalamus, optic optic chiasm

master biological clock

entrains circadian rhythms

light - zeitgeber "(‘time giver”)

pathway for light → biological clock

light → retinal ganglion cells → retinohypothalamic tract → SCN → pineal gland → melatonin

melatonin 

promotes sleep-like state, more produced when dark

if the SCN is damaged

circadian rhythms disappear = arrhythmic

hamster transplant study findings

SCN sets circadian period

transplanted SCN changed rhythm to donors cycle

how sleep cycle changes at puberty 

delayed sleep phase

teens naturally go to bed/wake up later 

benefits of later school start times

better grades, less depression, fewer car wrecks

sleep in infants vs older adults

infants: short cycles, 50% rem

older adults: less total sleep, loss of stage 3 SWS

what records brain waves 

EEG

REM vs non-REM differences

REM: fast activity, atonia, dreams, irregular HR/BP

key signals of each stage

1: light sleep, vertex spikes

2: sleep spindles + K-complexes

3: delta waves (SWS, deep sleep)

REM: low amp/high freq, muscle paralysis, vivid dreams

typical sleep breakdown 

50% stage 2

20% REM

90-110 min cycles 

when dreams are most vivid

REM

nightmares vs night terrors

nightmares: REM, remember

night terrors: stage 3, intense fear, no memory

effects of sleep deprivation 

irritability, bad focus, microsleeps, slower reaction time 

during sleep recovery

extra SWS + more intense REM

4 major sleep functions

energy conservation

niche adaptation

body/brain restoration (GH released in SWS)

memory consolidation

forebrain role in sleep

generates SWS (GABA)

reticular formation role

promotes wakefulness

pons (subcoeruleus) role

triggers REM + paralysis (atonia)

hypothalamus role 

sleep state “switch”

narcolepsy

REM attacks, cataplexy, no SWS before REM

insomnia

sleep onset: trouble falling asleep

sleep-maintenance: trouble staying asleep

sleep apnea 

cant breathe during sleep

CPAP helps 

REM behavior disorder

no paralysis - act out dreams

night terrors/bedwetting/sleepwalking

stage 3; mostly kids; usually outgrown

SIDS

infant stops breathing during sleep

“back to sleep” prevention 

getting cranky/emotional when tired

amygdala overreacts, PFC control weakens

excited vs bored mornings

excited: increased dopamine/norepinehrine = alert

bored: lower dopamine/norepinephrine = fatigue