A 61-year-old develops progressive weakness with muscle atrophy and fasciculations, but also has hyperreflexia and spasticity. Sensation remains intact. The neurologist explains that the disease involves degeneration affecting two levels of the motor system, explaining the mixed exam findings. ALS affects:  

A 49-year-old presents with vague, cramping abdominal discomfort and nausea. He cannot point to a specific spot, describing the pain as “deep” and “all over,” with intermittent waves. On exam, there is minimal focal tenderness. You explain that the type of pain arising from internal organs is often hard to localize due to the way those afferent fibers enter the spinal cord and converge with somatic pathways. Which pain is most diffuse and poorly localized?  

A 57-year-old with long-standing diabetes reports “burning, tingling, electric shock” pain in both feet, worse at night, with decreased vibration sense on exam. He asks why it feels different from “normal pain” after an injury. You explain that this pattern reflects abnormal signaling from damaged nerves rather than tissue injury signaling. Neuropathic pain is best described as:  

A 59-year-old with chronic kidney disease misses multiple dialysis sessions and presents with weakness and palpitations. ECG shows tall, peaked T waves. You explain that the most dangerous electrophysiologic effect is from the electrolyte that has the greatest influence on the resting membrane potential (Vm), because it largely determines the transmembrane gradient at baseline. Which electrolyte abnormality most directly alters resting membrane potential?

A 76-year-old reports frequent nighttime awakenings, early morning waking, and nonrestorative sleep. He has osteoarthritis, nocturia due to BPH, and takes a beta-blocker, a diuretic, and an evening dose of an SSRI. He asks why sleep has become more fragmented as he’s aged. You explain that while aging changes sleep architecture, the most common drivers of clinically significant insomnia and fragmentation are comorbidities and medication effects. Which factor most disrupts sleep in older adults?  

A 36-year-old suffers a hypothalamic stroke and subsequently develops impaired thermoregulation, sleep-wake disruption, and abnormal appetite signaling. The team asks which structure functions as the primary integrator of autonomic and endocrine responses to maintain homeostasis. Which structure controls autonomic function?  

A 30-year-old with allergic asthma has immediate wheezing after cat exposure that improves with albuterol. Six hours later, he returns with recurrent bronchospasm, increased sputum, and worsening peak flows despite no re-exposure. Sputum shows prominent inflammatory cells. Which process most explains the late-phase worsening?  

A 47-year-old undergoes surgery and receives a medication that blocks nicotinic receptors at autonomic ganglia. Shortly after, she develops orthostatic hypotension and decreased GI motility. The team reviews which neurotransmitter is released by all preganglionic autonomic neurons (both sympathetic and parasympathetic) at the ganglion. Which neurotransmitter is used by all preganglionic ANS neurons?  

A term newborn of a mother who received routine prenatal care has no signs of infection. The parent asks why the infant is “not starting from zero” immunologically even before vaccines. Which factor provides the most important systemic protection in the first months?  

A 58-year-old works in construction and has years of unprotected noise exposure. He complains of persistent high-pitched ringing in both ears, worse at night. Otoscopic exam is normal. Audiometry shows high-frequency hearing loss. You explain that the most common mechanism relates to peripheral auditory damage, with downstream central “gain” changes contributing to the perception of sound without an external stimulus. Tinnitus most commonly results from: