Sleep and circadian cycles

What are 4 changes that occur during sleep?

• behaviour

• brain activity

• cellular structural changes like synaptic rearrangements

• gene expression

What are the 2 cycles during sleep?

non-REM and REM sleep (rapid eye movement)

What are behavioural specificities of sleep?

• reduced motor activity

• reduced response to stimulation

• stereotypic postures like closed eye in humans

• quite easy reversibility

What are 3 ways that physiological activity can be measured through electrical recordings of:

muscle mvt, eye mvt and brain activity respectively?

• muscle: electromyography

• eye: electro-oculography

• brain: electroencephalography

What does an electroencephalogram (EEG) measure?

synchronous, electrical activity from large populations of neurones in the brain

What causes the measurements of an EEG?

cellular, ionic movement which = electric field

How is an EEG set up? In what parts of the brain can it measure activity?

electrodes placed on the surface of the scalp to detect the electric fields + electrical amplifier + monitor

in many different at the same time

What are the advantages of an electroencephalogram?

• non-invasive

• easy to administer

• data easily gathered

• high temporal resolution (within milliseconds)

What is a main disadvantage of an electroencephalogram?

low spatial resolution bc only a large population of active neurons are detected

(further away from the source of the electrical source = smaller the signal so only big signals picked up)

What are the main types of brain waves and their frequency?

• beta - 13 to 30

• alpha - 8 to 13

• theta - 4 to 8

• delta - 0.5 to 4

What does it mean for a wave to have a frequency of 30 Hz?

Means that there are 30 periods within a second of neuronal activity

What are neuronal activity, metabolic rate and brain temperature like during non-REM sleep?

neuronal activity is low - not much AP firing between neurones

metabolism + temp at their lowest

What is sympathetic nervous system outflow like during sleep? How does this affect HR and BP?

decreased so HR and BP also decrease, PNS activity increases

How are muscle tone and reflexes affected by sleep?

remain intact

Describe the stage of drowsiness during non-REM sleep

• Awakened easily

• Eyes move slowly, rolling and muscle activity slows

• Sudden muscle contractions preceded by a sensation of falling

How long does drowsiness last?

several minutes

What type of voltage EEG activity is detected during stage 1 of non-REM sleep?

low voltage - 10 to 30 uV at about 20 Hz

What type of voltage EEG activity is detected during stage 2 of non-REM sleep?

background activity continues with added biphasic K complexes occurring episodically + bursts of sleep spindles

What are sinusoidal waves occurring during stage 2 of non-REM sleep called? What is their frequency?

sleep spindles, 12 to 14 Hz

Describe the stage of light sleep during non-REM sleep

• eye mvt stops and brain waves slow with occasional bursts of rapid brain waves

• body temp drops and HR slows preparing for sleep

What are the 4 stages of non-REM sleep?

• drowsiness

• light sleep

• deep sleep

• very deep sleep

What are 1 and 2 on this graph, depicting EEG activity during non-REM sleep? What do they show?

• 1: K complex

• 2: Sleep spindle

new parts of the brain start to become active

Describe deep sleep during non-REM sleep?

• very slow delta waves with high amplitude - 0.5 to 2 Hz

• sleepwalking, night terrors, talking during sleep, bedwetting - during transitions between non-REM and REM sleep

Describe very deep sleep

brain produces delta waves only

disorientation upon awakening for several minutes after

Describe REM sleep

Why is REM sleep paradoxical?

Mimics wakefulness!

• patients experiencing this stage are very similar to an awake subject - eyes move rapidly, maybe linked to intense dreams

• low voltage mixed frequency EEG

What are brain temp/metabolic rate like during REM sleep?

both rise so consistent with increased neural activity sometimes even greater than when awake

What are skeletal muscles like during REM sleep?

atonic-flaccid and paralysed

Which muscles remain active during REM sleep?

controlling mvts of the eye, middle ear ossicles and diaphragm - can still breathe!

Describe the alternation between stages of REM and non-REM sleep during the night?

• one block: stage 1 then 2 then 3 then 4 of non-REM are interrupted by bursts of REM sleep of about 8-10 mins

• Repeated four or five times per night-during each repetition, stages 3 & 4 decrease in duration and REM increases

At which stage of sleep will the first REM phase occur?

after about 70 to 80 minutes sleeper returns to stages 3 or 2 then first REM

What is the time from the first to the end of REM sleep?

90 to 110 minutes

What’s the distribution of different sleep phases during a young adult’s night?

non-REM:

• stage 1 : 5%

• stage 2: 50 - 60 %

• stages 3 and 4: 15-20%

REM: 20 to 25%

What are the 4 main structures involved in regulation of sleep?

• inhibition of motor control

• rhythmic behaviour in the Thalamus

• NE and 5-HT (serotonin) in brain stem

• Diffuse modulatory neurotransmission system

Define a diffuse modulatory neurotransmission system

networks of neurons that release NTs into the ECF, influencing large areas of the brain, rather than specific synapses, to modulate neuronal activity

What is the main structure involved in wakefulness? Specifically?

brain stem ! the locus coeruleus (LC)

What can a lesion in the brain stem cause?

sleep and coma

What can stimulation of neurons in the brain stem cause?

awakening

Overall, what is brain activity like during non-REM sleep?

• decreased firing in the brain stem (= sleep)

• spindles correlate with activity in the thalamus

• delta rhythms = activity in the thalamus

Overall, what is brain activity like during REM sleep?

• firing similar to in an awake state

• very little frontal lobe activity

• no activity in the raphe nuclei or locus coeruleus

• inhibition of motor neurons

What are a few theories of why we dream?

• exercises synapses when no external activity

• circuit testing

• memory consolidation

What type of rhythm do sleep and wakefulness follow? What is its periodicity?

circadian rhythm with periodicity of about 24 hrs

What essentially is a circadian cycle?

endogenous cycle that times sleep/wakefulness and can persist without environmental cues

What modulates circadian cycles?

environmental cues mainly light

What structure acts as the major internal clock for sleep?

suprachiasmatic nucleus (SCN) of anterior hypothalamus

What is the role of the SCN in generating biological clocks?

acts as a clock, when lesioned dampens down the circadian rhythm of sleep

Is the SNC responsible for sleep?

no, just timing of sleep

What is the role of the visual system in circadian rhythms?

detects light and transmits this info to the brain's master circadian clock to synchronize internal rhythms with the external light-dark cycle

What provides input to the suprachiasmatic nucleus? What organ is this in?

Intrinsically photosensitive ganglion cells

retina of the eye