Chapter_10_Book

Adrian's Experience with Narcolepsy

• Adrian's first awareness of his problem was as an adult, when he attempted to surprise his mother in the garden, leading to sudden physical weakness in his knees and back.

  • This experience led to a series of paralysis episodes occurring when he thought something would be humorous.

  • Fully conscious yet unable to move for 15-20 seconds.

• Significant incidents included collapsing at a zoo after joking with his daughters.

• Adrian notes that the trigger for his episodes is not laughing itself but doing something he finds funny:"...if I were to say something that I felt was very funny to you, there’s a good chance that I would end up on the floor."

• This chapter aims to explore the mechanisms of sleep and the underlying issues in Adrian's brain that contribute to these disturbances.

Biological Rhythms

• Definition: Repeating patterns during living processes; observed in various physiological measures (hormone levels, body temperature).

• Circadian Rhythm: A 24-hour biological cycle that regulates sleep-waking behavior.

• Ultradian Rhythm: Rhythms shorter than a day (minutes to hours).

• Infradian Rhythm: Biological events with a cycle longer than a day (e.g., human menstrual cycle).

Circadian Rhythms

• Regulated by an endogenous biological clock in the brain that synchronizes behavior to the external environment.

• Evidence shows that changes in light, especially seasonal alterations, can shift these rhythms (e.g., breeding behaviors in animals).

Mechanisms of Biological Clocks

• Endogenous Clocks: Circadian rhythms generated internally, with most mammals relying on this intrinsic timing.

• Experimentation with rodents, such as hamsters in a running wheel, indicates free-running cycles (individual activity rhythms) showing variances from typical 24-hour cycles, influenced by light cues.

• Phase Shift: Adjustment of biological rhythms in response to external signals (e.g., light).

Suprachiasmatic Nucleus (SCN)

• The SCN, located in the hypothalamus above the optic chiasm, is crucial for regulating circadian rhythms.

• Lesions in SCN can eliminate these rhythms, demonstrating its central role in circadian activity.

• Transplant experiments show that the SCN generates circadian rhythms, as evidenced by the circadian activity pattern following transplantation of SCN tissue.

  • Mutations like tau shorten activity cycles, further confirming the SCN's control over biological timing.

Light and Circadian Rhythms

• Light serves as a powerful zeitgeber (“time-giver”) to reset biological clocks.

• Retinal ganglion cells, sensitive to light, directly influence the SCN, facilitating light-based entrainment of the circadian rhythms.

• Melanopsin in these retinal cells allows them to detect light independent of traditional photoreceptors.

Sleep Stages

• Sleep occurs in stages defined by EEG activity:

  • Stage 1: Transition phase; characterized by alpha rhythms and vertex spikes.

  • Stage 2: Contains sleep spindles and K complexes.

  • Stage 3: Known as slow-wave sleep (SWS), identified by delta waves; most restorative state.

  • REM Sleep: Rapid eye movement phase characterized by low-amplitude, high-frequency waves resembling wakefulness, yet the body experiences muscle atonia.

Sleep Cycle

• Average duration of sleep cycles for adults is 90-110 minutes, repeating through the night, with sleep stages cycling through different periods.

• Early night prioritizes SWS, while later cycles feature increased REM sleep duration.

Impact of Aging on Sleep

• As humans age, sleep patterns change with decreased total sleep time and more fragmented sleep, particularly in SWS.

Sleep Disorders

• Narcolepsy: Characterized by episodes of uncontrollable sleep, including cataplexy triggered by emotional responses. Loss of orexin signaling in the hypothalamus correlates with this disorder.

• Insomnia: Ranges from difficulty falling asleep (sleep-onset insomnia) to difficulty staying asleep (sleep-maintenance insomnia). Various forms of intervention can help.

• Parasomnias: Involve abnormal sleep behaviors, including sleepwalking and night terrors, primarily affecting children.

• REM Behavior Disorder: Individuals act out dreams due to lack of muscle atonia during REM, leading to risk of injury.

Importance of Sleep Hygiene

• To promote better sleep, individuals should maintain consistent sleep routines, limit exposure to screens prior to sleep, and manage caffeine intake.

• Poor sleep hygiene can exacerbate insomnia and disrupt natural circadian rhythms.

• Effective strategies enhance sleep without the need for pharmacological interventions.