Sleep, Dreaming, and Circadian Rhythms

circadian rhythms

consistent cycle of body activity and behavior that occurs over around 24 hours, in humans we have daily cycles of hormone levels, digestive enzymes, blood pressure, body temperature, neurotransmitter activity, heart rate, and sleep and arousal

diurnal

sleep at night

nocturnal

sleep at day

crepuscular

sleep in the middle of the day, active at twilight

zeitgebers

external stimuli like sunlight that influence circadian rhythms, without sunlight most people would have circadian rhythms over 24 hours

free-running clock

circadian rhythm shown by animals if not provided zeitgebers like light/dark cycles, not always 24 hours

circannual cycles

yearly cycles, affect migration, hibernation, and sexual reproduction, influenced by temperature, food, and amount of sunlight

unihemispheric sleep

only half the brain goes through sleep cycles at a time, while the other hemisphere stays conscious (ex. dolphins and whales)

chronobiology

studies how the time of day affects the biology, physiology, and behavior of living organisms

suprachiasmatic nucleus

structure in the hypothalamus that plays and essential role in establishing and maintaining circadian rhythms, neurons within change the rate of firing depending on the time of day and how much light the eye is receiving

melanopsin

photopigment that is sensitive to blue light, cells in retina containing melanopsin send info directly to SCN

pineal gland

plays important role in circadian rhythms and sleep/wake cycles, secretes melatonin which acts as a feedback loop to the SCN to maintain a 24-hour cycle

habenula

also releases melatonin

polysomnography

instrument used in sleep lab that measures several physiological responses during sleep like EOG, EEG, and ECG

electrooculogram

measures eye movement and is used to identify stages of sleep

electroencephalogram

measures electrical activity of the cerebral cortex using electrodes placed on the skull, can detect different brain waves during sleep

beta waves

(12-38 Hz high frequency, low amplitude) associated with alert wakefulness and arousal

alpha waves

(8-12 Hz high frequency low amplitude) associated with a wakefully relaxed state

theta waves

(3-8 Hz low frequency high amplitude) associated with light sleep

delta waves

(0.2-3 Hz low frequency high amplitude) associated with deep sleep

non-REM sleep

slow-wave sleep (theta and delta) typically at the beginning of the night, sympathetic activity decreases, parasympathetic activity increases, slowing the heart rate, lowering blood pressure, relaxing muscle tone

stage 1 of sleep

transition between wakefulness and onset of sleep, transition between alpha and theta waves

stage 2 of sleep

light sleep when neurons in the brain become more synchronized, but there are also bursts of high-frequency waves (sleep spindles) and high-voltage waves (K-complexes) mixed in with lower-voltage EEG activity

stage 3 of sleep

slow-wave sleep, theta and delta waves, no muscle movement, breathing is slowed, blood pressure drops

REM sleep

associated with dreaming and high frequency brain activity, characterized by eyes moving back and forth, physiological arousal, high-frequency brain wave activity 

REM rebound

after sleep deprivation, the amount of REM sleep increases at the next opportunity to sleep

waste removal

cerebral spinal fluid removes metabolites, extra proteins, amino acids, and waste from an active brain through the glymphatic system

glymphatic system

tunnels created by astrocytes that are active during sleep and helps distribute important molecules around the brain in addition to getting rid of wastes

information processing theory of sleep

sleep is an important time to strengthen important memories and eliminate less important memories

freudian theory of why we dream

dreams represent unconscious wishes

activation-synthesis hypothesis

theory of dreaming in which the cortex is trying to make sense of the high activity in the brainstem, dreams themselves do not have underlying meaning 

continual-activation theory

declarative memories are processed during NREM sleep and procedural memories are processed during REM sleep

insomnia

inability to sleep associated with many health and psychological problems

sleep apnea

difficulty breathing during sleep causing a person to wake up suddenly

obstructive sleep apnea

most common cause of sleep apnea due to obstruction in the airways because the back of the throat relaxes

central sleep apnea

cessation of breathing caused by problems of the central nervous system particularly an area of the medulla called pre-Botzinger complex that controls rhythmic breaking

cataplexy

condition where the muscle paralysis depended upon during REM sleep happens when a person is awake, can be caused by the lack of the neurotransmitter hypocretin

narcolepsy

onset of feeling sleepy or loss of control of muscle movement during wakeful hours 

parasomnias

number of sleep disorders that affect movement and behavior during sleep such as sleep walking, night terrors, sleep paralysis, and REM sleep behavior disorder

sleep paralysis

inability to move or control muscles when awake, typically happens just before falling asleep or waking up

REM sleep behavior disorder

lack of muscle paralysis during REM sleep, a person acts out their dream

hypnotics

sleeping pills, help to induce or maintain sleep, continuous use can lead to tolerance and addiction

benzodiazepines

common type of sleep aid, GABA agonist

Z-drugs

GABA agonist that does not show the same level of side effects as benzodiazepines

antihypnotic

drugs like caffeine, cocaine, amphetamines, and tricyclic antidepressants that inhibit sleep

modafinil

an antihypnotic that causes the release of hypocretin, prescribed for sleep apnea or narcolepsy

caffeine

reduce drowsiness, adenosine antagonist, can improve attention, memory, and arousal at low doses