Navigating the stages of sleep
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Navigating the stages of sleep
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[post_date] => 2024-12-26 08:35:16
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[post_content] => Practice Passage (Question 1-5)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
As you sleep, your brain and body cycle through varying levels of brain wave activity and eye movement; even muscle tone and core body temperature change throughout the night. These levels can be broken down into four major stages: N1, N2, N3, and REM. REM refers to rapid eye movement, a major characteristic of this stage. REM is the stage where your most vivid dreams occur and is required to feel fully rested. It is also characterized by atonia caused by inhibition of the motor neurons.
N1, N2, and N3 are all non-rapid-eye-movement sleep stages, also called synchronized sleep, due to the nature of electroencephalogram (EEG) recordings during these periods. N1 is the onset of sleep, and when you experience “hypnic jerks” – often associated with the feeling of falling. N2, light sleep, is where you spend about 50% of your night. N3, known as deep sleep, is characterized by very slow brain waves. Sleepwalking, also known as somnambulism, occurs chiefly during this sleep stage.
As you fall asleep, you pass through N1, N2, N3, and back to N2 before achieving REM sleep. This typically occurs about 90 minutes after falling asleep, and the first REM will last about 20 minutes. As the night progresses, one spends more time in REM sleep, and less in N3. The average night of sleep includes five of these cycles.
Figure 1. A hypnogram tracking the stages of sleep throughout the night.
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[question] => What is atonia?
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[description] => Reason for the Correct Answer:
Atonia is caused by inhibition of motor neurons.
One continues to breathe, even during REM sleep.
Atonia happens during REM sleep, but not N1-N3.
Vivid dreams happen during REM sleep.
Atonia is skeletal muscle paralysis, thought to protect us from damaging effects of acting out our dreams.
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[answers] => Array
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[each_answer] => A. Skeletal muscle paralysis
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[each_answer] => B. Rapid muscle twitching
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[each_answer] => C. Complete muscle relaxation
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[each_answer] => D. Total muscle paralysis
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[1] => Array
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[quiz_unique_key] => 3873426850
[question] => Sleep spindles are little bursts of high frequency brain activity and are associated with maintaining tranquility during sleep. In what stage do sleep spindles first occur?
[value] => Array
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[answer] => 2
[description] => Reason for the Correct Answer:
N1 sleep is sometimes thought of as “relaxed wakefulness”, and the EEG activity resembles that of a very relaxed person.
Sleep spindles have been shown to help people stay asleep when presented with auditory stimulus.
N3 is referred to as deep sleep, and is very hard to rouse from.
Sleep spindles are characteristic of the N2 stage of sleep.
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[answers] => Array
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[each_answer] => A. N1
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[each_answer] => B. N2
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[each_answer] => C. REM
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[each_answer] => D. N3
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[2] => Array
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[quiz_unique_key] => 83407773
[question] => How many complete sleep cycles can be seen in Figure 1?
[value] => Array
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[answer] => 3
[description] => Reason for the Correct Answer:
The first cycle goes from the initial falling asleep through the end of the first REM stage.
On a hypnogram, REM sleep is the level below wakefulness.
There are 4 full REM stages, and thus 4 complete cycles in Figure 1.
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[each_answer] => A. 7
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[each_answer] => B. 5
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[each_answer] => C. 4
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[each_answer] => D. 6
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[quiz_unique_key] => 2261298308
[question] => If Figure 1 is the hypnogram of a person with somnambulism, during which stage do you expect the sleepwalking to occur?
[value] => Array
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[answer] => 4
[description] => Reason for the Correct Answer:
Somnambulism occurs during deep sleep, stage N3.
The order of sleep stages is N1 → N2 → N3 → N2 → REM
N3 sleep is seen at the bottom of a hypnogram, stage D.
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[question] => What do you expect the EEG readings of REM sleep to look like?
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[answer] => 2
[description] => Reason for the Correct Answer:
N1 – N3 are referred to as synchronous sleep stages.
Atonia is thought to be a mechanism to keep us still while our brains are active.
REM sleep shows up as high frequency saw-tooth waves on an EEG – it is a period of high activity in the brain.
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[each_answer] => A. full of sleep spindles and K complexes
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[each_answer] => C. very low frequency delta waves
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[each_answer] => D. alpha waves as seen in relaxed wakefulness
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