Sleep

Circadian Rhythms and Sleep

circaidian cycle: biologically programmed rhythms control a daily cycle of behaviors and changes, controls the sleep/wake rhythms, plays a role in appetite, activity and other behaviors
* linked to: sun rising and falling, temperature change, environmental stimuli, endogenous biological clock
suprachiasmic nucleus (SCN): region of the hypothalamus, regulates biological rhythms, promotes entrainment, recieves inputs from retinal cells, regulates other internal clocks throughout the body
* entrainment: synchronization with the 24hr light/datk schedule
pineal gland: dorsal to the midbrain, rostral to the cerebellum, regulates seasonal rhythms, SCN triggers mineal gland to secrete melatonin, hibernation
sleep: state of continuous and long lasting unconsciousness, can be reversed rapidly and easily, driven by circadian rhythms, homeostatic factoy is the bodys drive to maintain a stable physiological state

Stages of Sleep

3 key differences throughout sleep: brain waves, muscle activity, eye movement
sleep cycling: awake, 1.5 hour non-REM sleep stages 1,2,3, REM sleep consisting of rapid eye movements and dreaming, return to non-REM
* rem sleep begins every 90 minutes, time spent in rem increases throughout the night, timespent in stage 3 decreases throughout the night

electroencephalogram EEG: record summed electrical actiivity of the cortex
  * amplitude:height of waves
  * frequency
  * synchronized firing: high amplitude low frequency (non-REM)
  * unsynchronized firing: low amplitude hight frequency (awake and REM)
REM Sleep: rapid eye movement, desynchronized brain waves, sympathetic nervous system dominates, increased irregular HR, BP and respiration, dreaming, muscle twitches, muscle atonia
* muscle atonia: paralysis, large muscles of body lose their tone

Purpose of Sleep

slow wave sleep: brain energy conservation and learning (declarative memory)
* all animals sleep
rem sleep: neurodevelopment and learning (nondeclarative memory)
* land mammals and birds only
* rebound phenomena: individuals deprived of REM sleep when returned to normal sleep schedule spend more time in rem sleep
delta waves: require little metabolic energy
even when inconvenient: dolphins and whales go into slow rem sleep one hemisphere at a time
small animals: higher daytime activity longer sleep
sleep deprivation impairs cognitive not physical. state
most active brain regions when awake: most delta. waves during sleep
fetus: continuous rem sleep
infants (2-3mos): arrhythmic sleep ~15 hr/day 50% rem
Babies (2yr): sleep ~12hr per day 30% rem
Adults: sleep 6-8hr/day 20% rem
Rem is important for neural development
both slow-wave and rem sleep facilitate long-term memory consolidation
REM→nondeclarative memory: gained through practice
Slow wave→ declarative memory: facts, events, spatial relationships, brain reherses newly learned information
Learning: 1. nondeclarative visual discrimination task, nap, Test→rem improved nondeclarative memory
nondeclarative: tracing in mirror; declarative: learning paired words and tasks, nap without rem, test→slow wave. sleepimproved declarative learning task

Cortical Activity during Sleep

dreams: a sequence of thoughts sensations and images experienced during sleep, delusions and hallucinations
extrastriate cortex activity increases: visual hallucinations
prefrontal cortex activity decreases: reduced planning and organization
lucid dreaming: awarenes andcontrol over dreams, requires frontal lobe activation
increased acrivity in the motorcortex and subcortical motor regions during dreaming, but no movement is produced due toinhibition of motor neurons in the spinal cord
brain stem neurons are involved in sympathetic nervous system activated
most dreams are nightmares: 1. activity in the brain stem, interpreted by cortex,dream produced. 2. dream, cortical outputs are interpretedm fight or flight response is triggered by the brain stem
regional cerebral blood flow decreased comparedto waking and rem
activation of visual and auditory cortices→drea, liek imagery, most dreams occur during rem sleep

Neural Control of Sleep

adenosine: neuromodulator, promotes sleep
homeostaticmechanism: 1. awake, stored sugar in astrocytes is broken down, 2. extracellular adenosine increases, 3. accumulation of adenosine inhibits neural activity, 4. sleep, astrocytes renew sugar storage
acetylcholine: promote neural activations anc cortical desynchrony
* chollinergic neurons: in pons and basal forebrain increase cortical activity
* high levels and activity: awake or rem sleep
norepinephrine: promotes arousal and vigialance
* locus coeruleus: dorsal pons region, noradrenergiv release throughout the brain
* high levels and activity→awake
serotonin: promotes cortical arousal and locomotion
* raphe nucleus: pons region, serotonergic release throughout the brain
* high levels and activity→ awake or exiting rem
Histamine: promote cortical activation and arousal
* tuberomamillary nucleus: hypothalamus, histaminergic release throughout the bein, direct activation at cerebral cortex, indirect activation at basal forebrain and pons via ACh
* high levels and activity→ awake
orexin: hypocretin peptide neurotransmitter, regulates eating, metabolism, waking
* lateral thalamus orexinergic neurons project throughout the brain including other NT systems listed
* narcolepsy: lack of orexin→daytome drowsiness and sudden sleep attacks
preoptic area: anterior region of the hypothalamus, comprised of sleep neurons
sleep neurons: GABAnergic neurons, synapse at and inhibit pons and basal forebrain, locus coeruleus, raphe nuclei, ttuberomamillary nucleusm lateral hypothalamus
arousal promoting regions and sleep regions regulate to transitions: awake→ sleep:adenosine@sleep neurons, deep sleep→rem, rem→deep sleep, sleep→awake

Sleep Disorders

insomnia: difficulty falling asleep
* sleep apnea: difficulty breathing and sleeping at the same time→wake ip
* treatment: cognitive behavioral therapy, progressive relaxation and changes to sleep hygiene, hypnotics:GABAa agonists. and antihistamines (could lead to tolerance, rebound insomnia)
narcolepsy: neurological disorder, daytime drowsiness and sleep attacks
  * sleep attack: sudden overwhelming urge to sleep (2-5min) triggered by boredom and monotony
  * cataplexy: sudden loss of muscle tone (while conscious), inhibition of motor neurons in the spinal cord, triggered. by emotional reaction and physical effort
  * cause: immune disorder→loss of orexinergic neurons or mutation in orexin B receptor
  * treatment: simulation of catecholamine agonists and antidepressants serotonin and NE agonists
sleep paralysis: loss of muscle tone while falling asleep or waking,
hypnagogic hallucinations: sleep paralysis and dreaming while awake
rem sleep behavior disorder: fail to exhibit paralysis during rem sleep
* causes: neurodegeneration, brain injury
* treatment: benzodiazepines