Sleep and Biological Rhythms – Lecture Review

100 Question-and-Answer flashcards covering circadian rhythms, sleep stages, neural mechanisms, sleep disorders, and dreaming theories.

What did early psychologists believe determined sleep and wakefulness?

They believed it was dependent on external stimuli.

What theory did Curt Richter propose in 1922 regarding cycles of activity?

That the body generates its own cycles of activity and inactivity.

What are endogenous circannual rhythms?

Internal biological mechanisms that operate on an annual or yearly cycle.

Give two examples of circannual rhythms in animals.

Migratory patterns and animals storing food for the winter.

What are endogenous circadian rhythms?

Internal mechanisms that operate on an approximately 24-hour cycle.

Name at least three functions that follow circadian rhythms.

Sleep, eating and drinking, body temperature, hormone secretion, urination, and drug sensitivity.

What is the primary purpose of circadian rhythms?

To keep internal biological processes in phase with the external world.

Without external cues, how long is the average human circadian rhythm?

Slightly longer than 24 hours.

Define a zeitgeber.

A stimulus that resets the circadian rhythm (German for “time giver”).

List three common zeitgebers.

Sunlight, exercise, and meals (also tides, arousal, and temperature).

What can relying on non-sunlight zeitgebers cause?

Depression, irritability, and impaired job performance.

What is jet lag?

A disruption of circadian rhythms due to crossing time zones.

Name two common symptoms of jet lag.

Daytime sleepiness and nighttime sleeplessness (also poor concentration).

How does traveling west affect circadian rhythms?

It phase-delays them.

How does traveling east affect circadian rhythms?

It phase-advances them.

How does shift work typically affect sleep duration?

Sleep duration varies with timing, and circadian rhythms often fail to adjust fully.

What two conditions help night workers adapt better?

Sleeping in very dark rooms and working under bright lights.

How do circadian cycles differ among individuals?

Some people are morning types, while others are night (evening) types.

How do circadian preferences change as people age?

Children are usually morning types; adolescents shift toward eveningness.

Which gene is linked to morningness versus eveningness?

The Period 3 gene—long version → early riser; short version → late riser.

Name the three main biological clock mechanisms.

Suprachiasmatic nucleus (SCN), clock genes, and melatonin.

What is the suprachiasmatic nucleus (SCN)?

The main control center for circadian rhythms, located above the optic chiasm in the hypothalamus.

What happens when the SCN is damaged?

Body rhythms become inconsistent and unsynchronized.

How does the SCN generate circadian rhythms?

In a genetically controlled, unlearned manner.

What do isolated SCN cells continue to do in a dish?

Produce rhythmic action potentials.

Through what pathway does light reset the SCN?

The retinohypothalamic path, a branch of the optic nerve.

What are melanopsin-containing ganglion cells?

Special retinal cells that detect overall light levels without input from rods or cones.

Which two genes are crucial for circadian rhythm generation?

Period (PER) and Timeless (TIM).

What do PER and TIM proteins accomplish in the SCN?

They increase SCN neuron activity to regulate sleep and wakefulness.

What is a common effect of a PER gene mutation?

Abnormal circadian rhythms or poor alertness after sleep loss.

What is the pineal gland?

An endocrine gland regulated by the SCN that releases melatonin.

What is the primary effect of melatonin?

It increases sleepiness.

When does melatonin secretion typically begin each night?

About 2–3 hours before bedtime.

How does melatonin help reset the biological clock?

By acting on receptors in the SCN.

When can supplemental melatonin be used to phase-advance the clock?

In the afternoon.

How is sleep best described as a brain state?

An actively produced state with reduced activity and responsiveness.

How does sleep differ from coma or a vegetative state?

Sleep is reversible and marked by specific, organized brain activity patterns.

What did EEG studies reveal about sleep?

That sleep comprises multiple stages with distinct electrical patterns.

What is a polysomnograph?

A combined EEG and eye-movement recording used to study sleep.

What are alpha waves?

Brain waves present during relaxed wakefulness.

What occurs in Stage 1 sleep?

Irregular, low-voltage EEG waves and declining brain activity.

What two phenomena mark Stage 2 sleep?

Sleep spindles and K-complexes.

What are sleep spindles?

12–14 Hz bursts of brain waves lasting at least half a second.

What are K-complexes?

Sharp, high-amplitude waves linked to temporary neuron inhibition.

What characterizes slow-wave sleep (SWS)?

Large-amplitude slow EEG waves plus slowed heart, breathing, and brain activity.

During which stages does slow-wave sleep occur?

Stages 3 and 4.

What is REM sleep?

Sleep featuring rapid eye movements with mixed light and deep characteristics.

Why is REM sleep called paradoxical?

The brain is highly active while the body’s muscles are deeply relaxed.

What is NREM sleep?

All sleep stages except REM.

Approximately how long is one full sleep cycle?

About 90 minutes.

How do sleep stages change across the night?

Stages 3 & 4 shorten, while REM periods grow longer and more frequent.

Name five neurotransmitters involved in wakefulness and arousal.

Acetylcholine, norepinephrine, serotonin, histamine, and orexin.

What is the reticular formation?

A brainstem network crucial for arousal and wakefulness.

Define the pontomesencephalon.

A part of the reticular formation that maintains cortical arousal.

Which neurotransmitters are released by the pontomesencephalon?

Acetylcholine and glutamate.

What is the locus coeruleus?

A small brainstem nucleus that releases norepinephrine and enhances attention.

When is the locus coeruleus largely inactive?

During sleep.

How does the hypothalamus contribute to arousal?

It releases histamine and orexin to promote wakefulness.

What does histamine do in the brain?

Increases arousal by acting on the cerebral cortex.

What is the primary role of orexin (hypocretin)?

To maintain wakefulness and prevent unwanted sleep.

Low orexin levels are linked to which sleep disorder?

Narcolepsy.

What does the basal forebrain contribute to sleep regulation?

It releases GABA for inhibition and acetylcholine for arousal.

What is GABA’s main function during sleep?

It inhibits neurons to promote sleep and suppress intrusive activity.

What is happening in the brains of sleepwalkers?

Some brain areas are awake while others remain asleep.

What is sleep paralysis?

REM-like brain activity with temporary body paralysis upon waking.

During REM sleep, what happens to postural muscles?

They are completely relaxed (virtually paralyzed).

Which neurotransmitter level rises during REM sleep?

Acetylcholine.

Which two neurotransmitters decrease during REM sleep?

Serotonin and norepinephrine.

What are PGO waves?

High-amplitude electrical waves traveling from pons → LGN → occipital cortex during REM.

What two factors trigger the onset of REM sleep?

Activity in the pons and a drop in serotonin levels.

What is REM rebound?

An increase in REM frequency and intensity after it has been repeatedly interrupted.

Define insomnia.

Inadequate or non-refreshing sleep.

List three potential causes of insomnia.

Stress, pain, noise, diet, medications, or circadian misalignment.

What is sleep apnea?

Impaired breathing during sleep that causes frequent awakenings.

Name two symptoms of sleep apnea.

Daytime sleepiness and cognitive problems (also mood disturbances).

What is narcolepsy?

A disorder marked by sudden sleep attacks and REM intrusions during wakefulness.

List the four primary symptoms of narcolepsy.

Sleep attacks, cataplexy, sleep paralysis, and hypnagogic hallucinations.

What is cataplexy?

Sudden muscle weakness or paralysis triggered by strong emotions.

What causes most cases of narcolepsy?

Autoimmune loss of hypothalamic cells that produce orexin.

Name one common treatment for narcolepsy.

Stimulant drugs such as modafinil (also certain antidepressants).

What is periodic limb movement disorder?

Involuntary leg movements during NREM sleep.

Describe REM behavior disorder.

Acting out dreams because normal REM muscle inhibition fails.

REM behavior disorder is often associated with which conditions?

Neurodegenerative diseases like Parkinson’s disease.

What is a night terror?

A bout of intense anxiety during NREM sleep causing screaming or thrashing.

During which stage does sleepwalking usually occur?

Stage 3 or 4 (slow-wave sleep), not REM.

Who is most likely to sleepwalk?

Children, and some stressed or fatigued adults.

List four major functions of sleep.

Energy conservation, memory consolidation, brain restoration, and hormone regulation.

How does sleep conserve energy?

By lowering body temperature and reducing muscle activity.

In what way does sleep aid memory?

It strengthens new memories and replays them during sleep.

What is the glymphatic system?

A brain waste-clearance system that is more active during sleep.

What happens to growth hormone release during sleep?

It increases, especially during slow-wave sleep.

How does sleep influence immune function?

It enhances immunity by reducing stress hormones and promoting tissue repair.

What is the activation-synthesis hypothesis of dreaming?

Dreams are the brain’s attempt to make sense of spontaneous activity.

Which brain areas are notably activated during dreams?

The pons (via PGO waves) and visual areas of the occipital cortex.

What does the clinico-anatomical hypothesis propose about dreams?

Dreams reflect thinking with altered brain activity—low sensory and prefrontal input.

Why are dreams often illogical?

Because the prefrontal cortex is less active during REM sleep.

Why do dreams frequently contain strong emotions?

Because limbic structures like the amygdala are active during REM.

What causes the sudden scene changes common in dreams?

Weak connections between the hippocampus and cortex during REM.

What contributes to the vivid imagery experienced in dreams?

Increased activity in visual and temporal cortical areas.

Which brain areas are less active while dreaming?

The primary motor cortex, prefrontal cortex, and primary sensory areas.