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Adrenergic neuron
Adrenergic neuron: neuron whose primary neurotransmitter is epinephrine (adrenaline); noradrenergic neurons use norepinephrine. Includes postganglionic sympathetic fibers and brainstem C1/C2 and A1/A2/A6 cell groups with α2 autoreceptor feedback.
Adrenocorticotropic hormone
Adrenocorticotropic hormone (ACTH, corticotropin) is a 39-amino acid anterior pituitary peptide, cleaved from POMC, that drives cortisol production via the MC2R receptor in the HPA axis; disorders include Cushing syndrome and adrenal insufficiency.
Adrenomedullin
Adrenomedullin is a 52-amino-acid peptide hormone of the calcitonin family that regulates vascular tone and fluid balance, isolated in 1993 and elevated in sepsis and heart failure.
Adult neurogenesis
Adult neurogenesis is the production of functional new neurons in the adult brain, occurring mainly in the hippocampus and debated for humans, with recent single-cell studies finding progenitors.
Adult-onset foveomacular vitelliform dystrophy
Adult-onset foveomacular vitelliform dystrophy (AOFVD, Gass disease, pseudo-Best disease) is a rare macular pattern dystrophy with a yellow egg-yolk-like foveal lesion, adult onset, mostly sporadic inheritance, and slow vision loss.
Advanced trauma life support
Advanced Trauma Life Support (ATLS) is the American College of Surgeons' standardized trauma training course, developed in 1978 by James K. Styner, using the ABCDE (now xABCDE) primary survey, taught to over 50,000 learners yearly in 80+ countries.
Afferent nerve fiber
Afferent nerve fiber: sensory axons (also called afferent neurons, dorsal root fibers) carrying information from receptors to the CNS via dorsal roots; classified Aα, Aβ, Aδ, C or Lloyd groups I–IV by conduction velocity.
After-cataract
After-cataract, or posterior capsule opacification (PCO, ICD-11 9B10.22), is the most common complication of cataract surgery: residual lens epithelial cells cloud the posterior capsule, treated by outpatient Nd:YAG laser capsulotomy.
Afterimage
Afterimage: a visual illusion in which an image persists after the stimulus is removed; positive (same color) or negative (complementary color) forms, retinal and cortical mechanisms, Emmert's law, and clinical afterimage testing.
Afterload
Afterload: the mechanical load opposing ventricular ejection, defined as aortic input impedance with steady (SVR) and pulsatile components; also lumped as effective arterial elastance Ea = end-systolic pressure/stroke volume.
Age and health concerns about Donald Trump
Age and health concerns about Donald Trump: the oldest inaugurated U.S. president (80 in 2026), his White House physicals, chronic venous insufficiency, hand bruising, Montreal Cognitive Assessment claims rated False by PolitiFact, and disputed physician disclosures.
Age-associated cognitive decline
Age-associated cognitive decline (AACD, ICD-11 MB21.0) is normal, non-pathological cognitive aging: declines in processing speed, memory, and executive function from early adulthood, without loss of daily independence, distinct from MCI and dementia.
Agenesis of the corpus callosum
Agenesis of the corpus callosum (AgCC, ACC): congenital absence or partial absence of the brain's interhemispheric fiber bundle, occurring in about 1:4,000 births, diagnosed by imaging, mostly of unknown cause, with variable cognitive outcomes.
Aging brain
Aging brain: age-related structural, cellular, and cognitive changes in the brain, distinguished from dementia; covers cognitive reserve, brain-age imaging, and exercise, training, and lifestyle intervention evidence.
Airway Resistance
Airway resistance is the opposition to airflow caused by frictional forces in the airways of the lung; it depends chiefly on airway radius and is measured by body plethysmography, introduced in 1956.
Ajmaline
Ajmaline is a class 1A antiarrhythmic alkaloid from the roots of Rauvolfia serpentina, used in Europe and Japan to treat and diagnose abnormal heart rhythms.
Albert Lasker Award for Basic Medical Research
The Albert Lasker Award for Basic Medical Research is an annual prize for a fundamental discovery opening a new area of biomedical science, first awarded in 1946.
Alcoholic cardiomyopathy
Alcoholic cardiomyopathy (alcohol-induced cardiomyopathy) is a toxic dilated cardiomyopathy from heavy drinking, generally over 80 g/day for 5+ years; potentially reversible with abstinence, fatal (about 10%/year mortality) if heavy intake continues.
Alferminogene tadenovec
Alferminogene tadenovec (Generx, Ad5FGF-4, AGT-MI) is an unapproved adenovirus serotype 5 gene therapy expressing FGF-4 for refractory angina; AGENT-3/4 failed on placebo response, later phase 3 trials incomplete.
Algor mortis
Algor mortis is the postmortem cooling of a body after death, used with the Henssge nomogram to estimate the postmortem interval, typically within the first 24-80 hours, limited by ambient temperature, body mass, clothing, and refrigeration.
Allen's test
Allen's test (modified Allen test, MAT): bedside maneuver assessing radial and ulnar artery patency and palmar arch collateral circulation before radial artery puncture, cannulation, or harvest; color should return within 5–15 seconds; pooled sensitivity 57%, specificity 91%.
Allergic conjunctivitis
Allergic conjunctivitis, also called ocular allergy (SAC, PAC, VKC, AKC, GPC), is IgE-mediated mast-cell inflammation of the conjunctiva causing itchy, watery, red eyes; treated stepwise with avoidance, dual-action antihistamine drops, and immunotherapy.
Alpha motor neuron
Alpha motor neuron (α-motoneuron): large lower motor neuron of the spinal cord and brainstem that innervates extrafusal muscle fibers via acetylcholine, forms motor units, follows the size principle, and degenerates in ALS.
Alpha wave
Alpha wave (alpha rhythm, Berger rhythm): 8–13 Hz EEG oscillation over posterior scalp during relaxed eyes-closed wakefulness, discovered by Hans Berger in 1924, blocked by eye opening and attention, interpreted as pulsed functional inhibition.
Alpha-synuclein
Alpha-synuclein (α-synuclein, SNCA gene product) is a 140-residue presynaptic protein; misfolded β-sheet aggregates form Lewy bodies in Parkinson's disease, dementia with Lewy bodies, and MSA, and seed amplification assays detect it diagnostically.
ALS
ALS (amyotrophic lateral sclerosis, Lou Gehrig's disease) is a fatal motor neuron disease causing progressive paralysis; most die within 3-5 years of symptom onset; riluzole, edaravone, and tofersen are approved treatments.
ALS Functional Rating Scale - Revised
ALSFRS-R (ALS Functional Rating Scale-Revised), 12-item 0-48 ordinal scale for ALS disability across bulbar, fine motor, gross motor, and respiratory domains; 1999 Cedarbaum revision, standard clinical trial primary outcome.
ALS study (NCT00821132)
NCT00821132, "Genetics of Familial and Sporadic ALS," is a Northwestern University observational genetic study led by Teepu Siddique, running 1991 to 2023 with 13,521 enrollees, collecting blood, CSF, and tissue samples from ALS families to identify ALS risk genes.
ALS–frontotemporal spectrum
The ALS–frontotemporal spectrum is a continuum of neurodegenerative disease in which amyotrophic lateral sclerosis and frontotemporal dementia overlap, sharing TDP-43 pathology and C9orf72 genetics, formally termed ALS-FTSD.
Altered level of consciousness
Altered level of consciousness (ALOC), also called altered mental status, is decreased responsiveness to external stimuli, ranging from lethargy and confusion through stupor to coma, and accounts for up to 10% of emergency department complaints.