Sleep and Circadian Rhythms Flashcards
sleep is defined as…
change in behaviour change in brain activity structural changes gene expression consists of cycle if non REM and REM sleep
sleep is defined behaviourally as …
reduced motor activity
reduced response to stimulation
stereotypic postures (eyes closed, horizontal in humans)
relatively easily reversible
physiological activity can be measured using electrical recordings
muscle movements with eleectromyography - muscle activity, depolarised ions picked up electrodes
eye movements with electro - oculography
brain activity with electroencephalography
electroencephalography
measures synchronous electrical activity from large populations of neurons in brain
caused by cellular, ionic movement = creates electric field
one electrode records millions of neurons
electrodes placed on surface of scalp, linked to electrical amplifier - data easily gathered, easy to administer, non invasive, high temporal resolution - detects fast changes, low spatial resolution
electric fields follow on inverse square law so only cortical activity detectable
main types of brain waves
beta
alpha
theta
delta - largest amplitude
non REM sleep - 4 main stages
neuronal activity is low - not much action potential firing between neurons
metabolic rate and brain temperature at their lowest
heart rate and blood pressure decline - decreased sympathetic NS outflow
increased parasympathetic nervous system
muscle tone and reflexes in tact
stage 1
drowsiness
awakened easily
eyes slowly and muscle activity slows
many people experience sudden muscle contraction (sensation of falling)
transition from wake to onset of sleep lasts several mins
awake people show low voltage EEG activity
as they relax - sinusoidal alpha activity
stage 2
light sleep
eye movement stops and brain waves become slower with only occasional burst of rapid brain waves
body begins to prepare for deep sleep
body temperature drops, hear rate slows
characterised by bursts of sleep spindles and bipahsic waves called K complexes - occur episodically against background of continuous low voltage EEG activity
sleep spindles
bursts of sinusoidal waves, high frequency waves
stage 3
deep sleep
very slow delta waves interspersed with smaller, faster waves
sleepwalking, night terrors, talking, ‘parasomnia’ - during transition between non REM and REM sleep
high amplitude, slow delta waves
stage 4
very deep sleep
brain produces delta waves almost exclusively
disorientation for several minutes following arousal from stage 4
slow wave activity increases and dominates the EEG record
stage 3 and 4 = slow wave sleep
stage 5
REM sleep EEG mimics awake, REM also found in birds closed eyes move rapidly side to side intense dream and brain activity 'paradoxical sleep'
during REM sleep
brain temp and metabolic rate increase - consistent with increased neural activity, in some areas, greater than in waking
all skeletal muscles are atonic - flaccid and paralysed
muscles controlling eye movement, middle ear ossicles and diaphragm remain active
normal sleeping pattern - humans
REM and non REM alternate cyclically
stage 1 - 4 then,
after 70/80 mins, return to stage 3 or 2 before entering 1st REM phase which lasts 8-10 mins
time from 1st stage to end of REM = 90 mins
repeated 4 or 5 times a night - stages 3 and 4 dec in duraton an REM increases
in young adults:
only 5% spent in stage 1
largest amount in stage 2 - 50%/60%
stages 3 and 4 = 15-20%
REM = 20-25%
