Lecture 21: Arousal - wakefulness and sleep

Question 1

What is wakefulness? Describe in terms of EEG, movement, thoughts and sensation. Describe the neural centres and neural centres involved in wakefulness

Answer 1

Wakefulness can be described as an active brain in a moveable body with an active state of consciousness.

• EEG during wakefulness is low voltage and fast consisting mostly of alpha and beta waves
• Movement is continuous and voluntary
• Thoughts are generally logical and progressive
• Sensation is vivid and externally generated

During wakefulness there is an increase in activity in the following neural centres:

• locus coeruleus (noradrenalin)
• reticular formation (acetylcholine)
• raphe nucleus (serotonin)

Question 2

Describe non-REM in terms of EEG, ANS, movement, thoughts and sensation. Describe what happens to the neural centres involved in non-REM sleep

Answer 2

• EEG during wakefulness is high voltage and slow theta and delta rhythms
• Movement: decrease in muscle tone and movement (except adjustments, sleep talk and sleep walking.)
• Thoughts : unknown
• Sensation is dull/absent
• ANS: increase in parasympathetic activity - decrease in temperature, HR, respiration, energy use, kidney

During non-REM sleep there is a decrease in activity in the following neural centres:

• decrease of noradrenalin in the locus coeruleus
• decrease of acetylcholine in the reticular formation
• decrease of seratonergic activity in raphe nucleus

Question 3

Describe REM in terms of EEG, ANS, movement, thoughts and sensation. Describe what happens to the neural centres involved in REM sleep

Answer 3

REM sleep is also known as paradoxical sleep because it is characterised by a highly active brain in an immovable body

• EEG during wakefulness is low voltage and fast beta waves
• Movement is characterised by paralysis and atonia exept respiratory muscles (which move barely), muscles of the eyes and inner ear muscles
• Thoughts are vivid, bizarre and illogical
• Sensation is vivid and internally generated
• ANS: Increase in HR, respiration, oxygen use, bloodflow to penis/clitoris (regardless of sexual dreams) and a DECREASE in body temperature

_​_During REM sleep:

• Acetylcholine inhibition in spinal cord supresses movement
• Increase in acetylcholine activity in the pons which causes dreams
• Increase in cortical activity

Question 4

Describe the sleep cycle

Answer 4

• During a normal nights sleep one will cycle through different stages of non-REM and REM sleep
• The sleep cycle begins with stage 1 non-REM sleep, a fleeting stage of sleep that only lasts a few minutes and is characterised by theta rhythms and slow eye rolling movements
• It then proceeds to stage 2, a slightly deeper stage of sleep. Sleep spindles occur occasionally (triggered by thalamic pacemaker). as well as K-complexes (high amplitude - sharp wave). This stage usually lasts between 5-15 minutes
• Stage 3 begins with high amplitude, slow delta rhythms, eye and body movements are few
• Stage 4: the deepest stage of sleep consists of larger delta rhythms he stage lasting between 20-40 minutes
• Sleep then progresses into REM sleep with its fast beta and gamma rhythms. As the night progresses there is a general reduction in non-REM sleep and an increase in REM sleep. Half the nights REM sleep occurs in the last 1/3 of sleep.
• The longest periods of REM sleep can last between 30 - 50 minutes, however, each period of REM is followed by at least 30 minutes of non-REM before another period of REM can occur
• Sleep cycles generally last about 90 minutes and the brain cycles through these stages 4-5 times

Summary:

• Awake = alpha and beta waves
• Stage 1: theta waves
• Stage 2: theta waves with K complexes and sleep spindles
• Stage 3: delta waves
• Stage 4: larger delta waves
• REM sleep: beta waves

Question 5

What are the possible functions of sleep?

Answer 5

• It gives the body time to rest and recover

Non-REM sleep

• Recovery - a period of restoration
• Adaption - out of sight from predators

REM sleep

• Memory formation

Question 6

Which stage of sleep does sleep walking and talking occur?

Answer 6

Stage 4 of non-REM sleep characterised by large delta waves

Question 7

Which stage of sleep to sleep spindles and K complexes occur?

Answer 7

Stage 2 of non-REM sleep between theta waves