Sleep, Stress and Dependence Flashcards
What proportion of the UK population reports disrupted or disordered sleep every year?
Around 2/3 of the entire population, costing society upwards of £40bn/annum.
What does sleep have direct roles to play in?
1) Attention
2) Mood regulation
3) Cognitive performance
4) Empathy
5) Social interaction
6) Immune system function
What may occur if sleep is disrupted?
1) Reduced attention span
2) Increased irritability
3) Increased interpersonal conflict
4) Illness
5) Work absenteeism
6) Reduced productivity
7) Increased workplace errors
What are the 2 main processes that drive sleep?
1) Sleep homeostat: the longer you are awake, the more you want to sleep. Wakefulness leads to sleep debt (sleep pressure), when sleep debt reaches a critical point, humans fall asleep.
2) Circadian process: a peak of alertness is felt mid-morning, it dips in the afternoon and peaks again early evening, before dipping once again. This is believed to exist as an evolutionary advantage, to ensure hunting and hiding at the most advantageous time of day.
How do molecules regulate sleep homeostasis?
These molecules also have a role to play in energy metabolism, neurodegeneration and immune function. On such molecules is adenosine, which is involved in energy metabolism. Levels of adenosine increase the longer one is awake, caffeine works by the absorption of adenosine to promote wakefulness.
What is the circadian rhythm?
This system dictates a pattern of physiological responses over a 24 hour period and is dictated by zeitgebers. Every aspect of human physiology and behaviour has an ideal 24 hour rhythm (e.g. temperature, blood pressure, serum cortisol levels, altertness and mood). Photosensitive retinal ganglion cells, do not play a role in vision, but send signals regarding the brightness of the surrounding environment. When light (the main zeitgeber) hits the retina, the ganglion cells transmit this signal to a set of nuclei called the superchiasmatic neuclei (SCN), located at the thalamus, at the base of the brain. These nuclei are known as the “master clock” and coordinate time throughout the rest of the body. They communicate via the hormone melatonin.
How do sleep systems vary between individuals?
1) Some people’s homeostat builds quicker and dissipated more slowly, meaning that they have a greater sleep need.
2) Some people have a different timing, performing better in the evening or morning.
3) The system change over time, between 10-21, the clock delays, so adolescents are biologically set for bed later. This delay reverses with age.
What is Polysomnography (PSG)?
This is the gold standard measurement of sleep, whose purpose is to allow for the diagnosis or different sleep disorders and to aid understanding of the dynamic nature of sleep and how different types of sleep impact day time functioning.
How is polysomnography set up?
1) Electectroencephalogram (EEG): electrodes on the scalp to measure electrical activity in the brain or brainwaves.
2) Electromyography (EMG): electrodes on the chin to measure muscle tone.
3) Electrooculography (EOG): electrodes either side of the eyes to measure eye movements.
How many stages is sleep divided into?
Sleep is divided into 4 distinct stages, with each stage having a unique brainwave signature and other unique physiological features.
1) Stage 1: the transition from wake to sleep in which humans can be easily awakened and experience sudden dreaming.
2) Stage 2: the brain begins to suppress outside stimuli (e.g. ambient noise, light). Deprivation of this stage impairs memory the following day.
3) Stage 3: also known as ‘deep sleep’ or ‘slow-wave sleep’, has a keep role in learning. It is difficult so wake from this stage of sleep. Heart rate, blood pressure and muscle activity are all much lower relative to wake. Night terrors, sleep walking and sleep talking occur in this stage of sleep. Being woken during stage 3 sleep will leave humans feeling drowsy and grumpy.
4) Rapid eye movement (REM): brain activity resembles awake brain activity, in fact the brain consumes even more energy during this stage, than it does during wakefulness. They’re are 2 key features of this stage - eyes jive arihnd in a distinctive and rhythmic way and the body is paralysed. This is because REM sleep is associated with vivid dreaming and paralysis prevents humans from acting out their dreams. This stage is also associated with increases in heart rate, blood pressure and body temperature. Being awoken in this stage of sleep leaves humans feeling confused and emotional, or even unable to move their bodies for a few minutes. This stage of sleep is key in helping learn new and complex skills, as well as emotional memory consolidation and emotional control.
What is a hypnogram?
Each minute of PSG output is scored as being one of the four stages of sleep, and can be summarised on a hypnogram. A hypnogram indicates the proportion of sleep spent in each stage throughout the night. Humans cycle through the sleep stages in a certain order and the proportion of time spent in each stage varies according to the duration of sleep.
Define sleep architecture
The structuring and timing of an individual’s sleep stages. A healthy sleeper would have most REM sleep in the second half of the night and most deep sleep in the first half of the night, with each cycle taking around 90 minutes. This means that 4-5 cycles should typically completed per night.
How do waken behaviours impact sleep quality
Waken behaviours impact sleep quality via the sleep homeostat. This is evident through changes in sleep architecture, as after extended periods of wakefulness or sleep deprivation, deep sleep increases through the night - rebound sleep. Both acute and habitual exercise impact the amount of deep and REM sleep seen throughout the night, showing a bidirectional relationship. The better one sleeps, the better they exercise and the better one exercises, the better one sleeps. Alcohol consumption leads to fragmented sleep, particularly in the morning; more REM sleep in the first half of the night, and less deep sleep over all. Depression can disrupt REM sleep, causing it to occur earlier than usual.
What is a false economy of sleep?
The belief that extending wakefulness to get more done, when in reality as tiredness increases, productivity decreases.
Define orthosomnia
A new sleep disorder where individuals are obsessed with getting a perfect night’s sleep, or over interpreting normal night variants as signs of disease.
