CNS 2 -sleep wae

How is consciousness defined, and what are the four states of consciousness in decreasing order?

• Consciousness is awareness of the external world or surroundings.

In decreasing order, the states are:

• maximum alertness

• wakefulness

• sleep

• coma

Who first recorded human brain electrical activity using an EEG, and what did they observe?

• Hans Berger in 1924

• He observed rhythmic wave activity while the subject was awake and relaxed, which he named alpha waves.

What are the main EEG brain wave frequency bands from slowest to fastest?

• Very Low Frequency (VLF): <1 Hz

• Delta: 1–3 Hz

• Theta: 4–7 Hz

• Alpha: 7–14 Hz

• Beta: 15–30 Hz

• Gamma: 30–100 Hz

• High Gamma: 80–150 Hz

• Very High Frequency (VHF): >150 Hz

How do the EEG patterns and durations differ across the stages of a single sleep cycle?

• A person goes through 5–6 NREM–REM cycles per night:

  • Stage I NREM (3–5% | 5–10 mins): 4–8 Hz activity.

  • Stage II NREM (50–60% | 30–40 mins): Characterized by sleep spindles.

  • Stages III & IV NREM (10–20% | 10–20 mins): Deep slow-wave sleep featuring 2–4 Hz slow waves (Stage III) and 0.5–2 Hz delta waves (Stage IV).

  • REM Sleep (10–20% | 10–20 mins): High-frequency EEG pattern similar to an awake state; REM duration increases with each subsequent cycle.

Why is REM sleep referred to as "paradoxical sleep"?

• Because even though the person is asleep with decreased body muscle tone and rapid eye movements, their EEG pattern abruptly becomes high-frequency and resembles that of an awake, alert person

What is unihemispheric slow-wave sleep?

• A sleep phenomenon seen in cetaceans (such as beluga whales and dolphins) where one hemisphere of the brain exhibits slow-wave sleep while the other hemisphere remains awake

What did Giuseppe Moruzzi (1949) and Walter Hess demonstrate about the brain mechanisms of sleep and wakefulness?

• Moruzzi found that stimulating cholinergic (ACh) cells in the brainstem between the pons and midbrain—termed the Reticular Activating System (RAS)—caused arousal and wakefulness.

• Walter Hess found that low-frequency stimulation of the thalamus in an awake cat induced sleep, showing that both sleep and wakefulness are active brain states

Which brain regions and neurotransmitters promote wakefulness versus sleep?

• Wakefulness: Driven by the ascending arousal system, which includes cholinergic (ACh) input to the thalamus, and noradrenaline (NA), serotonin (5-HT), histamine, dopamine (DA), and orexin (ORX) input to the cortex.

• Sleep: Driven by the Ventrolateral Preoptic Nucleus (VLPO) ("sleep centre") in the hypothalamus, which releases GABA (and galanin) to inhibit the Reticular Activating System.

How do benzodiazepines and caffeine affect sleep?

• Benzodiazepines promote drowsiness and sleep by potentiating the inhibitory effect of GABA, whereas caffeine inhibits sleep and promotes wakefulness.

What are the four main functions of sleep?

• Memory consolidation (associated with dreaming in REM sleep).

• Metabolic recovery (glycogen replenishment).

• General functional wellbeing (including immune system maintenance).

• Waste product removal via the glymphatic system.

How does the glymphatic system clear waste during sleep?

• It uses convective flow of cerebrospinal fluid (CSF) from para-arterial spaces through the interstitial fluid (ISF)—facilitated by astrocyte aquaporin-4 (AQP4) water channels—to flush metabolic waste out via para-venous efflux.

What is the difference between insomnia and sleep apnoea?

• Insomnia: Difficulty falling asleep or staying asleep as long as desired, triggered by factors such as stress, anxiety, depression, noise, alcohol/drugs, jetlag, or shift work.

• Sleep apnoea: A disruption to breathing during sleep—defined as airflow reduced by >50% for 10 seconds at a time—caused by relaxation of throat muscles or a lack of respiratory drive.

How does Computed Tomography (CT) work, and what are its limitations?

• CT builds an image of the brain based on the differential absorption of X-rays (bone absorbs X-rays well, air and water very little, and soft tissue in between).

• It reveals gross brain features but does not resolve fine structural details well (~£2M).

How does Magnetic Resonance Imaging (MRI) differ from CT?

• MRI is a medical application of nuclear magnetic resonance that uses strong magnetic fields, magnetic field gradients, and radio waves to measure the response of protons.

• It provides much higher anatomical resolution than CT (~£3M).

How does functional MRI (fMRI) measure brain activity?

• fMRI detects changes in blood oxygenation and blood flow that occur when active brain areas consume more oxygen, producing activation maps showing which brain regions are involved in specific mental tasks.

What does Positron Emission Tomography (PET) measure?

• PET maps functional and metabolic brain processes by detecting positrons emitted from decaying short-lived radioactive tracers, such as fluorodeoxyglucose (FDG), which highlight metabolically active tissue (~£1.5M).

What is Magnetoencephalography (MEG), and what is a key clinical use?

• MEG measures the magnetic fields generated by electrical activity in the brain using extremely sensitive devices called SQUIDs. Clinically, it is used to map functional brain areas and localize pathologies such as epileptic seizures.

What is the main advantage of Electroencephalography (EEG) compared to other neuroimaging methods?

• Aside from being cheap, quick, and non-invasive, EEG has exceptionally high temporal resolution, capable of detecting changes in electrical brain activity on a millisecond level.