The Demand for Sleep Flashcards
KKDP 2
Suprachiasmatic Nucleus
Located in the hypothalamus, the suprachiasmatic nucleus (SCN) is considered to be the master biological clock that regulates the timing and acti ty of the sleep-wake cycle.
A pair of pinhead-sized structures that together contain about 20,000 neurons. Responds to light and controls the production of melatonin.
Melatonin
A hormone secreted by the pineal gland in relation to the amount of light that is detected, influencing alertness, drowsiness and timing of the sleep-wake cycle.
● Involved in the initiation of sleep and the regulation of the sleep-wake cycle.
● Higher levels of melatonin are associated with greater drowsiness and ce
versa.
● The amount of melatonin that is secreted varies with the amount of light that
is detected by the SCN.
Melatonin Release
Melatonin secretion is stimulated by detection of light. In order to be released into the body:
1. Light is detected by the eye
2. This stimulates the suprachiasmatic nucleus (SCN)
3. The SCN signals the pineal gland in the hypothalamus to release melatonin.
Ultradian Rhythms
An ultradian rhythm is a biological rhythm that involves physiological, psychological or beha vioural changes that occur as part of a cycle shorter than 24 hours.
● The best known ultradian rhythm is human sleep.
○ Occurs as a sequence of distinctly different states and stages, each with
distinct physiological differences.
○ Generally a complete sleep cycle lasts approx. 90 minutes.
Types of Sleep
NREM: Non-rapid eye movement sleep consisting of 3 stages REM: Rapid eye movement sleep
NREM Sleep
● 75-80% of total sleep time is spent here; more in the first half of night than the second half.
● Di ded into three key stages (NREM 1 - 3) ranging from lightest to deepest, each with its own distinguishable pattern of physiological acti ty.
● Brain is not as active as when in REM sleep
● NREM is thought to restore us physically (repairing body tissue; remo ving waste; replenishing neurotransmitters)
Sleep Onset
The transition period from being awake to asleep is known as sleep onset.
The time it takes to fall asleep once the attempt to do so is made is known as sleep latency.
NREM 1
● NREM 1 is the lightest stage of sleep and has a low arousal threshold…and if woken we may not believe we have been asleep
Physiological changes
● Heart Rate decreases
● Breathing rate slows
● Temperature dropping
● Theta Brain waves
● Muscle tension relaxing
● Slow, rolling eye movements likely to be observed
Sleep Phenomena
Hypnic jerk - muscle spasm of the body or body part
Duration
Approx. 5 minutes Approx. 4-5% of total sleep time
NREM 2
NREM 2 is light sleep (sometimes referred to as true sleep). A slightly higher arousal threshold than NREM 1
Physiological changes
● Breathing rate regulated, body movements lessen, blood pressure and temperature continue to drop, heart rate slower
● Mostly Theta brain waves
Sleep Phenomena
Sleep Spindles - brief bursts (1 second) of rapid brain waves
Duration
10 - 25 minutes of first cycle and increases over sleep episode
NREM 3
● NREM 3 is deep sleep. A highest arousal threshold - it is difficult to wake a person during this stage (disoriented when woken).
Physiological changes
● Heart rate, blood pressure & temperature continue to drop.
● Breathing rate continues slow and steady
● Muscles relaxed
● Mostly Delta brain waves
Sleep Phenomena
Sleep walking, sleep talking, bed wetting and night terrors
Duration
Approx. 20 - 40 mins of first cycle and decreases over night (may be absent in second half of night). Approx. 10-15% of total sleep time
REM Sleep
REM Sleep: Rapid eye movement sleep. AKA paradoxical sleep or dream sleep (internally the brain is active, but the body is still).
● Arousal threshold varies depending upon when in the REM cycle a person is woken
Physiological changes
● More active than NREM
● Heart rate and breathing faster and irregular.
● BP rises.
● Muscle tension is at its lowest (paradoxical sleep).
● Eyes dart below the lids
● Brainwaves akin to alert wakefulness (generally Beta)
Sleep Phenomena
Dreaming & sleep paralysis
Duration
First for the night very brief (1-5 minutes)
➡
More time in REM in second half of night (up to an hour) Accounts for 20-25% of total sleep time
Arousal Thresholds
Low Arousal Threshold = wakes up easily (think NREM 1) High Arousal Threshold = harder to wake up (think NREM 3)
Hypongraph
The experiences of these stages vary across the night and can be seen in a
hypnograph
The Sleep Cycle
A complete sleep cycle consists of the NREM sleep with transitions between the 3 stages (but not necessarily all its stages) and periods of REM There is REM sleep in ➡
every cycle, even if it’s short.
● A typical healthy young adult will repeat each cycle 5 to 6 times each night. While lengths can vary from person to person
○ The average length of a sleep cycle is commonly described as approximately 90 minutes
