Noradrenergic arousal — MRCPsych Paper A MCQ

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EasyNeurophysiology and neurochemistryNoradrenergic arousalMRCPsych Paper A

A 25-year-old woman experiences sudden episodes of intense fear accompanied by tremor, palpitations and sweating. Which neurotransmitter–anatomical source pairing is most closely associated with the arousal and sympathetic autonomic activation described?

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Correct answer: D — Noradrenaline — locus coeruleus

Explanation lettering: C = shown as A · A = shown as B · D = shown as C · E = shown as D · B = shown as E

E is correct. The locus coeruleus is the brain's major noradrenergic nucleus and contributes to alertness, threat-related arousal and autonomic regulation. Its activation increases sympathetic activity, fitting the tremor, palpitations and sweating described. Basal forebrain acetylcholine contributes to cortical arousal and attention but is not the best pairing for sympathetic autonomic activation. Histamine from the tuberomammillary nucleus promotes wakefulness but is less directly linked to this autonomic pattern. Nigrostriatal dopamine from the substantia nigra primarily regulates movement, while somatostatin is an inhibitory neuropeptide expressed by subsets of cortical interneurones rather than the principal transmitter of an ascending arousal system. Panic is neurobiologically multifactorial, but among these options the noradrenaline–locus coeruleus pairing is the single best answer.

Reference: Samuels ER, Szabadi E. Functional neuroanatomy of the noradrenergic locus coeruleus: its roles in the regulation of arousal and autonomic function part I: principles of functional organisation. Current Neuropharmacology. 2008;6(3):235–253. https://pubmed.ncbi.nlm.nih.gov/19506723/