Biological Rhythms and Sleep – Review Flashcards

What is a biological rhythm?

A regular fluctuation in any living process, such as hormone secretion or sleep-wake cycles.

How long is a circadian rhythm, and give one human example.

About 24 hours; example: the human sleep-wake (rest/activity) cycle.

What are ultradian rhythms? Provide one example.

Rhythms that repeat more than once a day; e.g., the 90–110 min mammalian sleep cycle.

Define infradian rhythms and give an example.

Rhythms that repeat less than once per day; e.g., the human menstrual cycle.

Which part of the hypothalamus houses the master circadian clock?

The suprachiasmatic nucleus (SCN), located above the optic chiasm.

What evidence shows that circadian rhythms are endogenous?

In constant dim light, animals and humans show free-running rhythms slightly longer than 24 h, demonstrating internally generated timing.

What is a Zeitgeber?

An external cue, such as light, that entrains an organism’s circadian rhythm.

Which retinal cells convey light information to the SCN?

Specialized retinal ganglion cells that form the retinohypothalamic pathway.

How does light affect melatonin release?

Light inhibits pineal melatonin secretion; darkness increases it.

What happened when hamsters with SCN lesions received an SCN transplant from a 20-h-cycle donor?

Their circadian rhythms returned but adopted the donor’s 20-hour period, proving the SCN generates the rhythm.

How does adolescent circadian timing typically shift at puberty?

Toward later sleep and wake times (delayed phase).

List two benefits observed when high schools start after 8:30 AM.

Improved academic performance and 70 % fewer car crashes (also less in-class sleep and lower depression).

Which instrument records brain electrical activity to study sleep stages?

The electroencephalograph (EEG).

Name the two main categories of sleep.

Rapid-eye-movement (REM) sleep and Non-REM (NREM) sleep.

Describe the EEG pattern of alert wakefulness.

Low-amplitude, high-frequency beta activity (desynchronized).

Which two hallmark waveforms appear in Stage 2 sleep?

Sleep spindles and K-complexes.

What EEG feature defines Slow-Wave Sleep (Stage 3)?

Large-amplitude, low-frequency delta waves.

List three physiological characteristics of REM sleep.

Rapid eye movements, muscle atonia, and irregular breathing/heart rate with fast, low-amplitude EEG.

During a typical young adult night, what proportion is REM?

Approximately 20 % of total sleep time.

Which sleep cycles contain more Stage 3 SWS—early or late in the night?

Early cycles contain more Stage 3 SWS.

According to the activation-synthesis hypothesis, why do we dream?

Dreams are the cortex’s attempt to make sense of random brainstem activity during REM.

Differentiate between nightmares and night terrors.

Nightmares occur in REM and are remembered; night terrors arise from Stage 3 SWS, trigger autonomic arousal, and are usually not remembered.

How does total Stage 3 sleep change from age 20 to age 90?

It declines dramatically and may disappear entirely by age 90.

List three cognitive or mood effects of sleep deprivation.

Increased irritability, difficulty concentrating, and episodes of disorientation.

What sleep stages rebound after prolonged deprivation?

Extra Stage 3 SWS and more intense REM sleep occur during recovery.

Name the four proposed biological functions of sleep.

Energy conservation, niche adaptation, body/brain restoration, and memory consolidation.

Which forebrain region promotes SWS via GABA release?

The basal forebrain.

What is the role of the reticular formation in sleep?

It activates the forebrain to promote wakefulness.

Which pontine area triggers REM sleep and causes atonia?

The subcoeruleus region of the pons.

How does the hypothalamus contribute to sleep regulation?

It contains a ‘switch’ that coordinates transitions among wakefulness, NREM, and REM sleep.

What are two hallmark symptoms of narcolepsy?

Frequent REM sleep attacks and cataplexy (sudden loss of muscle tone without loss of consciousness).

During which sleep stage do night terrors and sleepwalking typically occur?

Stage 3 Slow-Wave Sleep.

Differentiate sleep-onset and sleep-maintenance insomnia.

Sleep-onset: difficulty falling asleep; sleep-maintenance: difficulty staying asleep or early awakening.

What is obstructive sleep apnea and one common treatment?

Repeated breathing cessation during sleep due to airway collapse; treated with CPAP (continuous positive airway pressure).

What characterizes REM behavior disorder (RBD)?

Acting out dreams during REM because normal muscle paralysis is absent.

Which infant sleep disorder is associated with immature respiratory systems?

Sudden Infant Death Syndrome (SIDS).

Why can long-term use of benzodiazepine sleeping pills be problematic?

They alter sleep architecture, lose efficacy, and cause next-day drowsiness and memory gaps.

Name three core principles of good sleep hygiene.

Go to bed only when sleepy, wake at the same time daily, and avoid caffeine and screens before bedtime.

Which brain areas show hyperactivity after sleep deprivation, contributing to emotional reactivity?

The amygdala shows increased activity while prefrontal-amygdala connectivity weakens.

How much longer do women on average need to sleep than men, according to studies?

Approximately 11–20 minutes more per night.

What is sleep inertia and when is it most likely to occur?

Grogginess after waking, particularly from deep Stage 3 sleep, often following oversleeping.

What molecule builds up during wakefulness to induce sleep pressure?

Adenosine.

Which two proteins form a dimer to initiate transcription of per and cry genes in the SCN?

Clock and Cycle proteins.

How do PER and CRY proteins regulate their own production?

They dimerize and feed back to inhibit Clock/Cycle activity, creating a ~24-hour cycle.

What genetic factor likely explains why some people are ‘larks’ and others ‘owls’?

Different variants (polymorphisms) of clock genes such as Clock, Per, or Cry.

What experimental manipulation abolishes circadian rhythms in mammals?

Lesioning (destroying) the SCN.

How does melatonin differ from prescription hypnotics in promoting sleep?

Melatonin does not force sleep; it signals darkness to promote a sleep-like state and is useful for short-term circadian adjustment.

What is cataplexy and with which disorder is it associated?

Sudden loss of muscle tone without losing consciousness, associated with narcolepsy.

Which sleep stage shows the greatest growth hormone release?

Stage 3 Slow-Wave Sleep.

Why do newborns spend about 50 % of their sleep in REM?

REM may provide vital stimulation necessary for nervous-system development.

What is microsleep and why is it dangerous?

Brief, involuntary sleep episodes lasting seconds; they impair performance and can cause accidents (e.g., while driving).

Explain sleep state misperception.

A condition in which people believe they are awake even though objective measures show they have slept.

Which neurotransmitters promote wakefulness during emotional arousal?

Dopamine (DA) and norepinephrine (NE).

Why does blue light at night hinder sleep?

It suppresses melatonin secretion, delaying sleep onset.

Provide one piece of evidence that REM is not strictly required for learning.

Studies show that while certain perceptual tasks benefit from REM, other forms of learning, especially declarative memory, rely more on SWS.

What effect does stimulating the basal forebrain have on sleep?

It induces Slow-Wave Sleep.

What effect does lesioning the reticular formation have?

It can induce continuous sleep due to loss of wake-promoting activity