Rhythms and Sleep Flashcards
What is a circadian rhythm?
Pattern that lasts approx. 24 hrs (ex. sleep)
- Correlated with activity in posterior part of cortex
- Persists without light
Define Zeitgeber
- Stimulus that resets the circadian rhythm
- ex. light, exercise, arousal, meals, environment, temperature
- Social stimuli are ineffective
How does jet lag effect the circadian rhythm?
- Disruption in circadian rhythm due to crossing time zones
- Sleepiness during the day, sleeplessness at night
- Results in phase delay or phase advance
What is the difference between phase delay and phase advance
Phase Delay:
- Going west - Stay awake later and wake up later - Easier to go west than east
Phase Advance:
- Going east - Go to sleep and wake up earlier
What are the genes involved in sleeping patterns
Period (PER) gene produces PER protein
Timeless (TIM) gene produce TIM protein
TIM and PER protein promotes sleep and inactivity, oscillating in concentration
- PER and TIM start low at the beginning of the day and increase at night
Based on 24 hr feedback system
- light activates a chemical that breaks down the TIM protein, increasing wakefulness and synchronizing the internal clock to the external world
What did De Mairan study?
- Heliotropic plants in 1729
- Put plants inside cellar without light but leaves still open during the day time
- Shows that they have a circadian clock
Describe the circadian rhythm studies on crickets
- Crickets sleep during the day, active at night, males call at dusk
Used LD and LL to measure calling patterns
Further Experiments:
- Separate the retina from the optic lobe
- LD shows free running
- Separate optic lobe from the rest of the brain
- Arhythmic calling
Conclusions of cricket studies
- Have entrained cycle that is exactly 24 hrs in LD
- Exhibit free running cycle of 26 hrs in LL
- Further experiments shows that their internal clock is somewhere in the optic lobes
What is an entrained cycle?
Uses zeitgebers to make cycle more exact
Describe the circadian rhythm studies on hamsters
- An electrolytic lesion to SCN eliminates the circadian rhythms and makes harder to entrain
- Can also take SCN out of brain (in vitro)
- Given the right nutrients, the SCN will continue to show rhythmic patterns
- Transplant SCN to animal with a SCN lesion to restore rhythms
Conclusions of hamster studies
- SCN acts as a clock and produces its own patterns even without any external stimuli
Pineal gland function
- Secretes melatonin into the blood during darkness which increases sleepiness
- Tumours in gland lead to disrupted sleep
Describe the circadian rhythm studies in drosophila
- Benzer used random mutagenesis to measure circadian rhythms
- Eclosion assay: come out of pupa (eclose) in light conditions early in day
- Mapped 3 mutations on PER gene caused by single base pair mutations
- Eclosion assay: come out of pupa (eclose) in light conditions early in day
PER protein in drosophilia
- High levels of staining in photoreceptors in eyes and optic lobes
- Concentration of PER protein decreased during the day and increased at night
- Concentration of PER mRNA increased during the day and decreased at night
- Show negative feedback system by PER protein
Compare comas, vegetative states, brain death, and sleep
Coma: extended period of unconsciousness caused by head trauma, stroke, or disease
Vegetative state: alternate between sleep and moderate arousal but has no awareness
Brain death: no sign of brain activity or response to stimulus
Sleep: actively produced by a network of brain regions
Compare the stages in NREM
Stage 1:
- EEG has irregular, jagged, low voltage waves
- Eye movement reduced
Stage 2:
- Sleep spindles + K complexes
Slow wave sleep:
- Large amplitude waves
- Associated with decreased HR, breathing and brain activity
- Prodominates early in the night - Contains stage 3 (fewer slow waves) and stage 4 (more slow waves)
- Indicates that neuronal activity is highly synchronized
- Older adults have less slow wave sleep and more awakenings
What are sleep spindles
In stage 2 sleep
- Low amplitude
- Burst of 12-14 Hz waves for at least 1/2 sec
- Results from oscillating interactions between cells in the thalamus and cortex
- Increases after new learning and correlates with improvements in memory
What are K-complexes
In stage 2 sleep
- Sharp wave associated with temporary inhibition of neuronal firing
Describe REM sleep
EEG shows irregular low voltage, fast waves; Like light sleep
Muscles are very relaxed; Like deep sleep
- Pons + medulla send messages to inhibit motor neurons controlling large muscles
Prodominates later at night
Amount of REM depends on the time of day, not the length of sleep
-Activity increases in the pons triggering REM onset and limbic system
- Decreased activity in visual + motor cortex and dorsolateral prefrontal cortex
What is the sleep stage cycle?
1 → 2 → 3 → 4 → 4 → 3 → 2 → REM → Repeat back to 2
Cycle lasts 90 min
Describe PGO waves
- High amplitude
- Waves first detected in the pons → LGN → Occipital cortex
Functions of REM
- REM varies more than NREM between individuals and species
- Strengthening memory
- Shaking of eyes is to get sufficient oxygen to the corneas
Describe Somnambulism
- Individual is awake in their motor cortex while other parts of the brain are inactive
- Not alert enough to process information
- Most common in slow wave sleep
How is GABA used in sleep mechanisms?
- More GABA released during sleep
- Interferes with the spread of info by neurons
- Sleep can therefore be localized in one area with more inhibition in one than another
Describe lucid dreaming
- Individual becomes aware they are dreaming
- Activity occurring in the temporal and frontal cortex enables the conscious monitoring of dreams
Describe the SCN role in circadian rhythms
- Damage results in erratic body rhythms
- Continues to produce the circadian rhythm action potentials even when its neurons are disconnected/removed from the brain
- SCN controls pineal gland which secretes melatonin at night to increase sleepiness
Efferent projections: Reticular formation, locus coeruleus, basal forebrain
- SCN controls pineal gland which secretes melatonin at night to increase sleepiness
Effects of light on SCN
Retinohypothalamic path (small branch of optic nerve) goes from retina → SCN and alters SCN settings
- Originates from retinal ganglion cells that have photopigment called melanospinDescribe melanopsin
- Retinal ganglion cells with their own photopigment without input from rods and cones
- Respond directly to the overall amount of light (not instantaneous changes)
- Respond to blue (short) wavelengths
Reticular formation and sleep
- In midbrain, promotes wakefulness
- Damage leads to prolonged sleep
- Contains Pontomesencephalon
- Projects to Hypothalamus, thalamus, cortex, basal forebrain
What is the Pontomesencephalon?
In retiuclar formation
- Receives input from sensory systems and generates own activity
- Axons extend into forebrain
- Some axons release GABA — inhibits behavior, promotes slow-wave sleep
- Other axons release acetylcholine, glutamate, dopamine, producing arousal in hypothalamus + thalamus + basal forebrain. Regulates potassium levels to produce arousal
Locus coerulus and sleep
- Located in the pons
- Usually inactive but emits bursts of impulses in response to meaningful events, especially those associated with emotional arousal
- Releases norepinephrine to hypothalamus (SCN) and cortical areas in response to meaningful events
- Output increases “gain” — increases activity of most active neurons, decreases activity of less active
- Leads to enhanced attention to important information and memory
Hypothalamus and sleep
- Contains SCN, lateral hypothalamus and histaminergic neurons
What are histaminergic neurons
- Releases histamine (excitatory neurotransmitter)
- Enhances arousal and alertness
- Antihistamines counteract and produce drowsiness
Lateral hypothalamus and sleep
Contains orexin neurons
- Released from lateral and posterior nucleus
- Orexin stimulates ACh-releasing cells in basal forebrain to promote arousal/wakefulness
- Necessary for staying awake - There are few orexin neurons but they project widely
Basal forebrain and sleep
- Axons extend to thalamus and cortex
- Acetylcholine stimulates BFb cells that promote wakefulness
- Releases ACh and GABA
- Alzheimer’s produces damage in BFb
Describe Insomnia
- Inadequate sleep either from trouble falling asleep (phase delay) or waking up too early (phase advance)
Describe Sleep apnea
- Impaired breathing during sleep
- Caused by genetics, hormones, old age and obesity
Describe narcolepsy
Main Symptoms:
1. Frequent periods of sleepiness during the day
2. Occasional catalepsy — muscle weakness while awake
3. Sleep paralysis
4. Hypnagogic hallucinations
- Caused by a lack of hypothalamic cells producing orexin
- Individual alternates between short waking and sleepy periods
Hypothesis for why we dream
Activation-Synthesis Hypothesis:
- Dream represents an effort to make sense of sparse and distorted information - Predictions for this hypothesis are vague
Neurocognitive Hypothesis:
- Dreams is just thinking taking place under unusual conditions - Dreams begin with spontaneous brain activity related to recent memories
