Circadian Rhythms and Sleep 2024 - Tagged

Rhythms and Circadian Rhythm

  • Living in a rhythmic environment with various cycles: annual, seasonal, monthly, daily.

  • Evolutionary adaptation led to biological rhythms to coordinate with these environmental cycles.

Circadian Rhythm

  • Most evident cycle is the daily, or circadian, rhythm.

  • Physiological measures influenced by circadian rhythms:

    • Body temperature

    • Hormone release

    • Reaction to drugs

    • Sleep/wake state

  • Controlled by the suprachiasmatic nucleus:

    • Located in the brain, serves as the body's internal clock.

    • Contains neurons with intrinsic time-keeping properties.

Mechanism of the Suprachiasmatic Nucleus

  • Produces a protein that regulates the cycle:

    • Protein production increases, activates a trigger to stop production.

    • After reaching a low level, production resumes.

  • Cycle lasts approximately 24 hours but can run longer (24.5-25 hours) in absence of environmental cues (free-running clock).

Environmental Cues: Zeitgebers

  • Signals that reset daily rhythms, keeping them in sync with the external world.

    • Common zeitgebers: daily activities, meal times, and notably, light.

  • Light activates specialized ganglion cells in the eyes, conveying information to the suprachiasmatic nucleus.

Consequences of Circadian Rhythm Disruption

  • Misalignment between internal rhythms and external cues can lead to:

    • Changes in mood

    • Sleep disturbances

    • Alters cognitive abilities

  • Causes of desynchronization:

    • Daylight savings time

    • Jet lag

    • Night shift work

    • Developmental changes in adolescents

Resynchronizing Circadian Rhythms

  • Techniques to readjust internal clocks:

    • Exposure to bright, full-spectrum light at appropriate times.

    • Use of melatonin supplements to promote sleepiness and reset the clock.

Sleep Stages

Non-REM Sleep

  • Divided into Stages 1–4, each with distinct brain activity:

    • Stage 1: Transition between wakefulness and sleep; theta waves are present.

    • Stage 2: Characterized by sleep spindles and K complexes; individuals may not recognize they were asleep.

    • Stage 3: Presence of delta waves, indicating synchronized brain activity.

    • Stage 4: More than 50% delta waves; deepest sleep, challenging to wake an individual.

  • Stages 3 and 4 collectively referred to as slow-wave sleep (SWS).

REM Sleep

  • Occurs following non-REM stages; characterized by:

    • Paradoxical brain waves resembling wakefulness.

    • Rapid eye movement; vivid, story-like dreams.

    • Loss of muscle tone (temporary paralysis) during this stage.

  • Cycles through stages last approximately 90 minutes; REM periods lengthen as the night progresses.

Sleep Disorders

Insomnia

  • Difficulty in falling or staying asleep:

    • Onset insomnia: difficulty falling asleep.

    • Maintenance insomnia: difficulty staying asleep.

  • Insomnia can stem from:

    • Stress, pain, excitement, or depression.

    • Medications for sleep can create tolerance and dependence, leading to worsened sleep issues.

Sleep Apnea

  • Episodes of stopped breathing during sleep, needing treatment such as surgery or a breathing device.

Narcolepsy

  • Neurological disorder with symptoms including:

    • Sleep attacks at inappropriate times (2-30 minutes long).

    • Cataplexy: sudden loss of muscle tone causing collapse.

    • Sleep paralysis and hypnagogic hallucinations during paralysis.

  • Often genetic; linked to orexin dysfunction.

REM Sleep Disorder

  • Absence of paralysis during REM, leading individuals to act out dreams.

Slow-Wave Sleep Disorders

  • Include:

    • Bedwetting

    • Night terrors

    • Sleepwalking

  • More prominent in children; treatments vary, including alarm systems for bedwetting.

Kleine-Levin Syndrome

  • "Sleeping Beauty syndrome" characterized by lengthy, reversible sleep episodes.

  • Episodes can last days/weeks; completely normal between episodes; tends to affect adolescent males.