Biological Rhythms Flashcards
Describe the structure and function of the Suprachiasmatic Nucleus (SCN).
The SCN is a small region in the hypothalamus, directly above the optic chiasm. It’s responsible for controlling circadian rhythms. It receives direct light input from the retina, helping to synchronize the body’s internal clock with environmental light-dark cycles. The SCN regulates various bodily functions like sleep-wake cycles, hormone release, and body temperature.
What are Circadian Rhythms?
Circadian rhythms are approximately 24-hour cycles in the physiological processes of living organisms. They are driven by the body’s internal clock and influenced by environmental cues like light and temperature.
Describe the three standard physiological measures of sleep.
Electroencephalogram (EEG):
Measures brain wave activity.
Key in identifying sleep stages (N1, N2, N3, REM) based on brain wave patterns.
Electromyogram (EMG):
Records muscle activity and tone.
Important for detecting changes in muscle activity during REM (muscle atonia) and Non-REM sleep.
Electrooculogram (EOG):
Monitors eye movements.
Essential for identifying REM sleep (characterized by rapid eye movements)
Describe the three stages of the sleep EEG, and explain the difference between REM and non-REM sleep.
NREM Sleep Stages:
Stage 1 (N1): Light sleep, transition from wakefulness, increased theta waves.
Stage 2 (N2): Deeper sleep, characterized by sleep spindles and K-complexes.
Stage 3 (N3): Deep sleep (slow-wave sleep), delta waves, most restorative.
REM Sleep:
Features rapid eye movements, similar brain waves to wakefulness, muscle atonia, and vivid dreaming.
Differences:
Brain Waves: NREM progresses to slower waves; REM has awake-like waves.
Eye Movements/Muscle Activity: Only REM shows rapid eye movements and muscle paralysis.
Dreaming: More common and intense in REM.
Physiological Changes: Varied heart rate, breathing, brain activity between NREM and REM.
Sleep Cycle: NREM dominates early night; REM increases towards morning.
Describe the activation-synthesis theory of dreams.
Origin: Developed by J. Allan Hobson and Robert McCarley in the 1970s.
Random Brain Activation: During REM sleep, the brainstem generates random neural signals.
Cortical Synthesis: The brain’s cortex interprets these signals, creating a narrative or dream.
Dreams as Byproduct: Dreams are seen as byproducts of the brain’s effort to make sense of random neural activity during sleep.
No Inherent Meaning: Dreams don’t necessarily have meaningful psychological content, contrasting with psychoanalytic theories.
Neurobiological Focus: Emphasizes brain processes and neurochemistry in dream formation.
Describe the two kinds of theories of sleep.
Recuperation Theories:
- Sleep for body and brain recovery.
- Physical restoration (tissue repair, growth hormone release).
- Neurological restoration (clearing brain waste, memory consolidation).
- Supported by effects and reversals of sleep deprivation.
Evolutionary (Adaptive) Theories:
- Sleep as an adaptive response to environmental demands.
- Energy conservation during inefficient food search times.
- Safety during periods of vulnerability.
- Niche adaptation reflecting ecological and survival needs.
- Evidence in varied sleep patterns across species.
Explain how stress can often be a confounding variable when considering the effects of sleep deprivation.
Bidirectional Relationship: Stress can cause and result from sleep deprivation, complicating effect attribution.
Overlap in Effects: Both stress and sleep deprivation share similar effects (e.g., hormonal imbalances, mood changes, cognitive impairments), making it hard to differentiate causes.
Stress as a Mediator: Stress may mediate the relationship between sleep deprivation and its effects, adding complexity.
Individual Variability: People’s varied stress responses affect their reaction to sleep deprivation, challenging generalization.
Measurement Challenges: Difficulty in accurately measuring and separating stress from sleep deprivation effects in studies.
Describe the major effects of sleep deprivation in humans.
Cognitive: Reduced concentration, impaired judgment, memory issues.
Mood: Increased irritability, risk of depression and anxiety.
Physical Health: Higher risk of obesity, diabetes, heart disease, weakened immune system.
Motor Skills: Slowed reaction times, decreased motor coordination.
Perception: Potential for hallucinations in severe cases.
Hormonal: Disrupted growth and stress hormone balance.
Quality of Life: Lower energy, motivation, impaired work and social interactions.
Long-term Risks: Increased likelihood of chronic diseases like stroke, Alzheimer’s.
Describe the effects of REM-sleep deprivation.
Increased REM Pressure: Subsequent increase in REM sleep intensity and duration when allowed to sleep normally.
Mood and Cognitive Impairment: Irritability, anxiety, difficulty concentrating, memory problems.
Physiological Effects: Altered brain activity patterns, potential impact on learning and memory consolidation.
Rebound Effect: Marked increase in REM sleep following deprivation period.
Describe the circadian sleep–wake cycle and the role of zeitgebers in maintaining circadian rhythms.
Circadian Sleep-Wake Cycle: A 24-hour internal biological rhythm controlling sleep and wakefulness, regulated by the suprachiasmatic nucleus in the brain.
Zeitgebers (Time Givers): External cues that synchronize the body’s circadian rhythms with the 24-hour day.
Primary Zeitgeber: Light, crucial for resetting the circadian clock daily, influencing wakefulness and sleepiness.
Other Zeitgebers: Social interaction, physical activity, eating patterns, though less influential than light.
Importance: Alignment of internal cycle with external environment is vital for optimal health; disruptions can lead to sleep disorders and mood disturbances.
Describe free-running rhythms and internal desynchronization, and explain why they are incompatible with recuperation theories of sleep.
Free-Running Rhythms: Sleep patterns not synced to the 24-hour cycle, often longer or shorter, observed in environments without external time cues (like natural light).
Internal Desynchronization: Different internal circadian rhythms (like sleep-wake cycle, body temperature) become out of sync with each other, often due to irregular light exposure or sleep disorders.
Challenge to Recuperation Theories: These theories suggest sleep restores functions depleted during wakefulness, predicting a stable 24-hour sleep-wake cycle. However, free-running rhythms and desynchronization show sleep patterns can naturally deviate and misalign, indicating sleep’s role may extend beyond mere daily restoration.
How does the 24-hour light-dark cycle entrain the sleep-wake cycle and other circadian rhythms through the eyes and related neural pathways?
Research on the entrainment of circadian rhythms by the light-dark cycle focused on the eyes and neural pathways. Cutting the optic nerves before reaching the optic chiasm disrupts the entrainment of circadian rhythms by the light-dark cycle. However, cutting the optic tracts after they leave the optic chiasm does not affect this entrainment.
These findings suggest that visual axons critical for circadian rhythm entrainment branch off near the optic chiasm, leading to the discovery of the retinohypothalamic tracts.
These tracts project from the optic chiasm to the adjacent suprachiasmatic nuclei (SCN).
Surprisingly, rods and cones in the eyes are not necessary for this entrainment. Instead, the key photoreceptors are retinal ganglion cells containing melanopsin, mediating the ability of light to entrain circadian rhythms.
How do the SCN control circadian rhythms? The timing mechanisms of the SCN depend on the firing patterns of SCN neurons.
SCN neurons tend to be inactive at night, start to fire at dawn, and fire at a slow steady pace all day (see Belle & Piggins, 2012; Colwell, 2011; Mohawk & Takahashi, 2011).
Describe what happens to circadian rhythms in the absence of exogenous zeitgebers
Circadian rhythms in constant environments are said to be free-running rhythms, and their duration is called the free-running period. Free-running periods vary in length from individual to individual, are of relatively constant duration within a given individual, and are usually longer than 24 hours—about 24.2 hours is typical in humans living under constant moderate illumination (see Czeizler et al., 1999). It seems that we all have an internal biological clock that habitually runs a little slow unless it is entrained by time-related cues in the environment.
This phenomenon is called internal desynchronization
How might you expect a lesion the SCN to affect an individual?
Although SCN lesions do not greatly affect the amount of time mammals spend sleeping, they do abolish the circadian periodicity of sleep cycles.
