1. Sleep & Disorders

Why is sleep important?

• Sleep is essential for normal brain & body function

• Vital for survival

• Sleep deprivation can lead to death within 2–3 weeks, similar to starvation

What are the effects of inadequate sleep?

Reduction in:

• Performance, concentration, reaction times, learning

Increase in:

• Memory lapses, accidents, behavior & mood problems

What is measured in a polysomnographic analysis of sleep?

• Organ function:

  • Eye movements → Electrooculogram (EOG)

  • Muscle activity → Electromyogram (EMG)

  • Brain activity → Electroencephalogram (EEG)

• Physiological variables:

  • BP, temperature

  • Breathing monitoring

  • Video & sound monitoring

What are key features of brain waves in EEG recordings?

• Parameters:

  • Frequency → waves/sec (Hz)

  • Amplitude → wave height (µV)

• Synchrony:

  • Synchronised → waves align in time

  • Desynchronised → random timing

• Types of waves:

  • Beta: 14–30 Hz, < 20 µV

  • Alpha: 8–13 Hz, 25–100 µV

  • Theta: 4–7 Hz, ~20 µV

  • Delta: 0.5–4 Hz, 20–200 µV

Which neurotransmitters are involved in promoting wakefulness & where are they from?

• Glutamate → ARAS (midbrain, pons, reticular formation)

• Acetylcholine → Basal forebrain to cerebral cortex

• Serotonin → Dorsal raphe nucleus (brainstem), part of ARAS

• Noradrenaline → Locus coeruleus, part of ARAS

• Histamine → Tuberomammillary nucleus (hypothalamus), acts on cortex

• Dopamine → Ventral tegmental area (midbrain)

• Orexins → Lateral hypothalamus, project widely to regulate wakefulness

Which neurotransmitter is majorly involved in promoting sleep?

Gamma-aminobutyric acid (GABA), used by the VLPO of the hypothalamus along with galanin.

How does adenosine contribute to sleep?

• Adenosine builds up during prolonged wakefulness.

• It inhibits wakefulness-promoting neurons, reducing their activity = sleepiness

What is the role of melatonin in sleep?

Melatonin is a sleep-promoting hormone secreted by the pineal gland, synthesized from 5-hydroxytryptamine under the influence of the SCN (circadian clock) in the hypothalamus.

What happens to thalamic relay of sensory input during sleep?

• Awake: Sensory input = Thalamus = Cortex (info reaches the cortex)

• Asleep: Sensory input = Thalamus ≠ Cortex (relay is blocked)

• Thalamocortical neurones become less excitable during sleep, reducing sensory transmission to the cortex.

How is REM sleep controlled by pontine nuclei?

• REM sleep is initiated by pontine nuclei in the brainstem

• These nuclei activate:

  • Thalamus = promotes cortical activation

  • Medulla = inhibits motor neurones (muscle atonia – loss of muscle tone)

• Results in vivid dreaming with muscle paralysis (except eyes & diaphragm)

What is REM sleep & what are its features?

• REM (rapid eye movement) sleep is a sleep stage associated with dreaming

• Features:

  • 4–5 episodes per night

  • Episodes ↑ in duration toward morning

  • Rapid eye movements

  • Desynchronised EEG

  • Hippocampal theta activity

  • Muscle atonia (loss of muscle tone)

  • Vivid dreams