Single-unit recordings across the sleep-wake cycle show that firing of a pontine noradrenergic nucleus is highest during active wakefulness, decreases in NREM sleep, and becomes virtually silent during REM sleep. Which nucleus is being recorded?

• A Pedunculopontine tegmental nucleus
• B Nucleus accumbens
• C Raphe magnus
• D Locus coeruleus ✓

Explanation

The locus coeruleus is the principal source of CNS noradrenaline. Its tonic firing maintains cortical arousal and attention during wakefulness, slows in NREM sleep, and ceases almost completely in REM sleep, which is why exogenous noradrenergic agents suppress REM. The pedunculopontine and laterodorsal tegmental nuclei are cholinergic and behave oppositely, increasing their firing during REM sleep.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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