Sleep and Circadian Rhythm Flashcards
(9 cards)
The Two Drives of Sleep
Sleep is controlled mainly by two processes:
- Homeostatic (S) - if we do not sleep we accumulate sleep debt
- Circadian (C) – sleep tends to happen at a particular time during the 24-hour cycle
The Study of Sleep
Polysomnography - The ‘gold standard’ of sleep research discovered by Hans Berger (1929)
EEG recordings (electroencephalogram): recordings of activity of populations of neurons in the brain underneath the skull
EOG recordings (electrooculogram): recordings of activity of the muscles around the eyes to decipher eye movements
EMG recordings (electromyogram): recordings of the activity of the muscles in the body
These recordings can be combined with others such as heart rate, temperature, breathing (O2) etc.
Brain activity during wakefulness
During wakefulness, different types of neuronal activity are observed in the EEG recording:
- Beta waves consist of irregular activity of 13–30 Hz.
Beta activity takes place when the brain is processing information
The person is alert and attentive to events in the environment or engaging in cognitive processes - Alpha waves consist of activity of 8–12 Hz.
Occur when a person is resting quietly, not particularly aroused or excited and not engaged in strenuous mental activity
Brain activity during sleep
Sleep begins with a state of relaxation, feeling drowsy
Stage 1 (3.5–7.5 Hz): presence of theta activity - it is a transition between sleep and wakefulness
Stage 2: Sleep begins – characterized by irregular activity and also sleep spindles (12-14Hz) although these occur in other stages of sleep and K complexes which are only found during stage 2.
Stage 3: High-amplitude and low-frequency delta activity (less than 3.5 Hz). Referred to as Slow-wave sleep (SWS)
REM Sleep: Increased brain activity and asynchrony in brain waves accompanied by muscle atonia (paralysis). Rapid Eye Movement (REM)
Stages 1,2,3 = NREM sleep
Each stage lasts approximately 90 minutes
Is sleep induced by a neural substance?
Many natural substances cause sleep i.e. morphine
Neurochemicals and hormones can produce sleep-wake cycles
Adenosine: Accumulates during the day, after prolonged wakefulness and promotes sleep.
Caffeine antagonizes the effects of adenosine and decreases sleepiness.
Orexin/Hypocretin:
- It is a peptide released from the lateral hypothalamus (LH)
- Highly responsible for the maintenance of wakefulness
- Implicated in narcolepsy
Brain regions important to sleep
ventro-lateral preoptic area (vlPOA) which contains inhibitory neurotransmitters such as GABA
- Damage to this area causes insomnia in rats and they eventually die
- Electrical stimulation of this area causes sleepiness and sleep
The reticular formation (Reticular Activating System-RAS) is responsible for wakefulness.
- It is comprised by a group of nuclei in the brainstem that send projections to the forebrain to promote arousal
Why do we sleep?
Sleep is adaptive - Conserves energy
Sleep is restorative - Helps feeling refreshed in the morning, removes free radicals and toxic waste buildup in the brain
Sleep promotes development - REM sleep is 50% in infants vs 20-25% in adults
Sleep facilitates cognition - learning and memory, problem solving and creativity
Circadian Rhythm
Endogenous cycles (“generated from within”) - our brain and body spontaneously generate their own rhythms based on the earth’s rotation.
- control other functions, such as body temp, hormone secretion, urination, etc
Zeitgebers - external cues to biological clock - e.g. light, meals, activity, temp
Jet-Lag: Traveling west “phase-delays” our circadian rhythms whereas traveling east “phase-advances” our circadian rhythms (people find the latter more difficult).
Chronotypes: morning “larks” (older) and evening “owls” (younger) - differences in wakefullness
Suprachiasmatic Nucleus - the biological clock
The primary biological clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus
Lesions of this nucleus disrupted circadian rhythms of wheel running, drinking, hormonal secretion, etc. and was thus named “the master clock”
The SCN receives information about light through the retinohypothalamic tract, formed by a special population of ganglion cells (photosensitive retinal ganglion cells-PRGCs) which make up ~1-3% of ganglion cells
The SCN regulates behaviour, including waking and sleeping, by controlling activity levels in other brain areas and secretory glands such as the pituitary (light phase) and the pineal (dark phase) gland
Transplantation of an SCN into a donor organism results in the recipient following the donor’s rhythm
Breeding of animals is controlled by the SCN via the pineal gland
