📌 Professor’s Notes: Quick Revision
High-yield revision notes for rapid review before university examinations.
- Electroencephalogram (EEG) is a noninvasive recording of the brain’s electrical activity obtained from scalp electrodes. It mainly reflects summated postsynaptic potentials of cortical neurons and is influenced by the thalamus and reticular activating system (RAS). EEG is used in the diagnosis of epilepsy, sleep disorders, altered consciousness, and brain death.
- EEG waves are classified according to frequency and amplitude:
- Alpha (8–13 Hz): Seen in relaxed, awake individuals with eyes closed; disappears on eye opening (alpha block).
- Beta (13–30 Hz): Seen during alertness, concentration, and mental activity.
- Theta (4–8 Hz): Normal in children and during light non-rapid eye movement (NREM) sleep; persistent theta in awake adults suggests neurological dysfunction.
- Delta (0.5–4 Hz): Dominant during deep NREM sleep; persistent delta waves in awake adults indicate severe cerebral disease.
- Sleep is a reversible physiological state essential for growth, tissue repair, memory consolidation, learning, and normal brain function. It consists of repeated 70–90 minute cycles, beginning with NREM sleep followed by rapid eye movement (REM) sleep. NREM accounts for 75–80% and REM for 20–25% of total sleep.
- NREM sleep (slow-wave sleep) has four stages:
- Stage 1: Transition from wakefulness to sleep.
- Stage 2: Characterized by sleep spindles and K-complexes.
- Stages 3 and 4: Deep sleep with delta waves.
- During NREM sleep, heart rate, blood pressure, respiration, and body temperature decrease, while growth hormone secretion increases. NREM sleep is important for physical restoration and memory consolidation.
- REM (paradoxical) sleep is characterized by:
- Low-amplitude, high-frequency EEG resembling wakefulness.
- Rapid eye movements, vivid dreaming, muscle atonia, and ponto-geniculo-occipital (PGO) spikes.
- Variable heart rate, blood pressure, and respiration.
- REM sleep is essential for memory processing, emotional regulation, learning, and normal brain development.
- Regulation of sleep:
- Suprachiasmatic nucleus (SCN) acts as the biological clock and synchronizes the sleep–wake cycle with the light–dark cycle.
- Pineal gland secretes melatonin during darkness, promoting sleep.
- Important neurotransmitters include gamma-aminobutyric acid (GABA) (sleep), acetylcholine (REM sleep), serotonin, noradrenaline, histamine, and adenosine. Balanced interaction among these systems regulates normal sleep architecture.
- Clinical applications of EEG include diagnosis of epilepsy, localization of focal brain lesions, evaluation of sleep disorders, and confirmation of brain death. Absence seizures show characteristic 3-Hz spike-and-wave complexes on EEG.
- Important sleep disorders:
- Insomnia: Difficulty initiating or maintaining sleep.
- Narcolepsy: Excessive daytime sleepiness with cataplexy due to reduced orexin (hypocretin).
- Sleepwalking, night terrors, and nocturnal enuresis occur mainly during deep NREM sleep.
- Nightmares and REM sleep behavior disorder occur during REM sleep.
📝 Practice MCQs
🎙️ Frequently Asked Viva Questions
High-yield viva questions with concise answers for rapid university examination preparation.
Q1. What is the physiological basis of the electroencephalogram (EEG)?
Answer: EEG mainly records the summed postsynaptic potentials of cortical pyramidal neurons, not individual action potentials.
Q2. Why are EEG waves high in amplitude during deep sleep?
Answer: Deep sleep causes synchronized firing of cortical neurons, producing slow, high-amplitude EEG waves.
Q3. What is alpha block and what does it indicate?
Answer: Alpha block is the disappearance of alpha waves when the eyes open or during mental activity. It indicates increased cortical activation and alertness.
Q4. Differentiate alpha and beta waves.
Answer: Alpha waves (8–13 Hz) occur in relaxed wakefulness with eyes closed. Beta waves (13–30 Hz) occur during alertness, concentration, and active mental activity.
Q5. Why are delta waves considered abnormal in an awake adult?
Answer: Persistent delta waves during wakefulness usually indicate significant cerebral dysfunction or structural brain disease.
Q6. Why is REM sleep called paradoxical sleep?
Answer: REM sleep shows an EEG similar to wakefulness, but skeletal muscles are almost completely paralyzed, creating a paradoxical state.
Q7. What are the characteristic EEG features of Stage 2 NREM sleep?
Answer: Sleep spindles and K-complexes are the characteristic EEG features of Stage 2 NREM sleep.
Q8. What is the physiological role of sleep spindles?
Answer: Sleep spindles help memory consolidation and reduce responses to external sensory stimuli, helping maintain sleep.
Q9. Why is deep NREM sleep important?
Answer: Deep NREM sleep promotes physical restoration, tissue repair, energy conservation, and growth hormone secretion.
Q10. Differentiate NREM and REM sleep.
Answer: NREM: slow-wave EEG, reduced autonomic activity, no rapid eye movements. REM: wake-like EEG, rapid eye movements, vivid dreams, and muscle atonia.
Q11. Why does skeletal muscle atonia occur during REM sleep?
Answer: Brainstem pathways actively inhibit spinal motor neurons, preventing body movements during dreaming.
Q12. What is the function of the suprachiasmatic nucleus (SCN)?
Answer: The SCN is the biological clock that synchronizes the sleep–wake cycle with the environmental light–dark cycle.
Q13. How does melatonin regulate sleep?
Answer: Melatonin, secreted by the pineal gland during darkness, promotes sleep and synchronizes circadian rhythms.
Q14. Why is EEG important clinically?
Answer: EEG helps diagnose epilepsy, sleep disorders, altered consciousness, brain death, and other neurological disorders.
Q15. What is the physiological basis of narcolepsy?
Answer: Narcolepsy is strongly associated with reduced orexin (hypocretin) production by neurons of the lateral hypothalamus, leading to excessive daytime sleepiness and early REM sleep.
Click to see: Medical Disclaimer and Copyright Notice