On EEG recording, sleep spindles and K-complexes are characteristics of which stage of NREM sleep, and what neural structure generates sleep spindles?
- A Stage N2; generated by thalamic reticular nucleus bursting that rhythmically inhibits thalamocortical relay neurons at 12–15 Hz ✓
- B Stage N3; generated by hippocampal CA3 pyramidal neuron synchronisation at 0.5–2 Hz
- C Stage N1; generated by cortical layer V pyramidal cells producing sigma frequency oscillations
- D Stage REM; generated by pontine tegmentum bursting that transmits 12–15 Hz oscillations to cortex
Correct answer: A. Stage N2; generated by thalamic reticular nucleus bursting that rhythmically inhibits thalamocortical relay neurons at 12–15 Hz
Explanation
Sleep spindles (12–15 Hz, sigma waves) and K-complexes define NREM stage N2 sleep. Spindles are generated by thalamic reticular nucleus (TRN) GABAergic neurons that inhibit thalamocortical relay neurons in rhythmic bursts; the relay neurons subsequently rebound-burst and drive cortical spindle oscillations. K-complexes are large-amplitude slow waves initiated by external stimuli. Stage N3 is characterised by delta waves (0.5–2 Hz) representing slow oscillations from corticothalamic circuits. REM sleep produces low-amplitude mixed-frequency EEG, not spindles.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.