Rhythms & Sleep Flashcards
Circadian rhythms
Functions of a living organism that display a rhythm of about 24 hours
Diurnal animals
Like us
Nocturnal
Awake at night
Zeitgeber
A cue animals use to entrain or synchronize their schedules
Here, light is a zeitgeber to help entrain its cycle
Without any light cues
Without any light cues, the animal is still exhibiting a rhythm; it’s said to be free-running
Bottom portion is constant dim light
No zeitgeber, but still exhibits a rhythm
Circadian rhythms are generated by
An endogenous clock
Entrainment
The process of synchronizing the rhythm with external cues
Phase shift
The shift in activity in response to a synchronizing stimulus such as light or food
Period
Time between two similar points of successive cycles, may not be exactly 24 hours
A free-running animal
Maintains its own cycle without
external cues
Why have a circadian rhythm?
It synchronizes an animal’s behavior and body states to daily rhythms in the environment
The endogenous clock enables animals to anticipate an event and help with survival
Ex: nocturnal animal gets up too early, knows it needs to adjust and will do that accordingly
The hypothalamus houses a circadian clock
In the SCN– suprachiasmatic nucleus
Suprachiasmatic nucleus
Receives light input; responsible for programming time-keeping mechanisms
Lesions to SCN
Messes up rhythms
An animal uses light a little bit to help it synchronize
But without light, animal’s activity is all over the place
Circadian rhythms entrain to light-dark cycles using…
Different pathways, some outside of the eye
In amphibians and birds, the ___________ is sensitive to light
pineal gland
In mammals, light information goes from the eye to the SCN via the ________________
retinohypothalamic pathway
Retinohypothalamic pathway
Not all animals use it, but mammals do
Genetic component
Gene mutations show how important the clock is to behavior in constant conditions
Tau gene mutations
The period is shorter than normal
Double Clock gene mutants
Severely arrhythmic
Larks vs. night owls
People who feel energetic in the morning (“larks”) likely have different alleles of the Clock and per genes than “night owls”
Infradian rhythms
Some biological rhythms (infradian rhythms) are longer than a day, such as the 28-day human menstrual cycle
Annual rhythms
Many animal behaviors are characterized by annual rhythms, like season breeders and body weight
Exogenous factors
Some rhythms are driven by exogenous factors such as food availability and temperature
In the lab, you can change the light cycle to mimic winter and summer, and animals will behave accordingly
Siberian hamsters
Siberian hamsters suppress reproductive system and get silver coats in the fall to blend in with snow; brown coats when they’re reproducing
Ultradian rhythms
Rhythm that’s shorter than a day
Period length can be from minutes to hours
Sleep is synchronized to…
External events, including light and dark
In the absence of cues, many humans have a free-running
period of approximately __ hours
25
Electroencephalography (EEG) records…
Electrical activity in the brain
Electro-oculography (EOG) records…
Eye movements
Electromyography (EMG) records…
Muscle activity
Two distinct classes of sleep
Non-REM sleep
REM sleep
Non-REM sleep
Three stages; characterized by lack of eye movements
REM sleep
Characterized by small-amplitude, fast-EEG waves, no postural tension, and rapid eye movements
Stages of sleep
Waking
Stage 1 (non-REM)
Stage 2 (non-REM)
Stage 3 (non-REM)
REM sleep
Kittens
A) not in REM because of postural tension
B) no postural tension, REM state
Young adult sleep
Sleep time ranges from 7-8 hours
Cycles last 90-110 minutes
Cycles early in the night have more stage 3 SWS
Later cycles have more REM sleep
Most recuperative sleep
Stage 3
Most growth hormone released, body repairs itself
Sleep at puberty
At puberty circadian rhythm of sleep shifts in many people so that they get up later in the day
Nightmares
Nightmares are long frightening dreams that awaken the sleeper from REM sleep
Night terrors
Night terrors are sudden arousals from non-REM sleep, marked by fear and autonomic activity
Biological functions of sleep
Conserve energy
Enforce niche adaptation
Restore the body and brain
Aids in memory consolidation
Sleep and energy conservation
Small plant-eating animals sleep more than large ones because they burn more energy per gram of body weight
BUT no correlation between body size in predatory species
Sleep enforces niche adaptation
Sleep helps animals avoid predators; animals sleep during the part of the day when they are most vulnerable
Being nocturnal or diurnal is part of an animal’s ecological niche
Sleep restores the body and brain
Replenishing proteins
Producing growth hormone
Glymphatic system flushes waste (like beta-amyloids)
Sleep aids memory consolidation
The number of new dendritic spines in mice increased and were stronger after sleep, and decreased if they were sleep-deprived
Sleep improves declarative memory
Helps consolidate nondeclarative memory
At least four interacting neural systems underlie sleep
Forebrain system: Generates SWS
Brainstem system: Activates forebrain into wakefulness
Pons system: Triggers REM sleep
Hypothalamic system: Affects the other three
Acting out a dream
Lesion in locus coeruleus blocks inhibition from muscles during REM sleep
Sleep deprivation
Increased irritability, difficulty in concentrating, episodes of disorientation
Screens before bed feed light info to SCN
How to improve sleep
Going to bed and waking up at the same time
Not eating food before bed
