2,701 articles
Myocarditis
Myocarditis, inflammation of the heart muscle (myocardium), viral, immune, drug, and toxin causes; incidence 6–8 per 100,000, mRNA vaccine risk per million doses, diagnosis by Lake Louise CMR criteria and biopsy, outcomes and 2024–2025 guidelines.
Myocyte of sinoatrial node
Sinoatrial node myocyte (pacemaker cell, P cell): specialized small cardiac muscle cell of the heart's SAN that spontaneously generates impulses via membrane and calcium clocks, setting heart rate at 60–100 bpm.
Myofibril
Myofibril: the ~1 µm-wide cylindrical contractile organelle of striated muscle, built from 2.2–2.5 µm sarcomeres of actin and myosin filaments; sliding-filament ATP-driven contraction, titin mechanosensing, and myofibrillar myopathy.
Myokymia
Myokymia is involuntary, fine, rippling muscle contraction from repetitive motor-unit discharges; eyelid myokymia, the commonest form, is a benign eyelid twitch triggered by fatigue, stress, and caffeine, treated with botulinum toxin if persistent.
Myotome
Myotome: the group of skeletal muscles innervated by one spinal nerve ventral root, and the somite compartment forming skeletal muscle; used clinically to localize radiculopathy, though maps vary between patients.
Myringotomy
Myringotomy, or tympanotomy, is a surgical incision in the eardrum to drain middle ear fluid or ventilate the ear, often with a tympanostomy tube (grommet). First recorded in 1649; reintroduced by Schwartze and Politzer in the 19th century.
Nail (anatomy)
Nail (anatomy): the human fingernail or toenail, a keratin nail plate produced by the nail matrix, anchored by the nail bed, and bordered by folds, cuticle, lunula, and hyponychium; fingernails grow about 3 mm per month, toenails about 1.5 mm.
NAION trial
Clinical trials for non-arteritic anterior ischemic optic neuropathy (NAION): the IONDT surgical trial and small citicoline (CDP-choline) studies; no treatment has demonstrated proven efficacy.
Nanoparticle crossing of the placental barrier
Nanoparticle crossing of the placental barrier is the translocation of particles 1–100 nm from maternal circulation into placental tissue or the fetus, with size the key determinant.
Nap
Nap: a short period of daytime sleep, also called a siesta. Key facts: short naps restore alertness and cognition; waking from slow-wave sleep causes sleep inertia; naps over 30-60 minutes are linked to worse cardiovascular and mortality outcomes.
Naresh Trehan (नरेश त्रेहान)
Naresh Trehan (नरेश त्रेहान), born 1946, Indian cardiovascular and cardiothoracic surgeon; founder of Escorts Heart Institute (1988) and Medanta (2009); over 48,000 open-heart surgeries; Padma Shri and Padma Bhushan recipient.
Nasal cavity
Nasal cavity: the paired air space of the nose, also called nasal chambers, extending from nares to choanae. It warms, humidifies, and filters air, drains the paranasal sinuses, and houses olfactory receptors in its superior olfactory region.
Nasal concha
Nasal concha (turbinate): curved bony projection from the lateral nasal wall; three pairs (inferior, middle, superior) plus a variable supreme turbinate; middle and superior from ethmoid, inferior a separate bone; warm, humidify, and direct airflow.
Nasal cycle
Nasal cycle: ultradian rhythm of alternating congestion and decongestion of the nasal turbinates, shifting airflow dominance between nostrils every ~2 hours awake and ~4.5 hours asleep, present in 70–80% of adults, driven by autonomic tone and first described by Kayser in 1895.
Nasal septum
Nasal septum (septum nasi): the midline bone-and-cartilage partition dividing the nasal cavity into two halves, formed by the ethmoid's perpendicular plate, vomer, and quadrangular cartilage; commonly deviated, corrected by septoplasty.
National Cardiovascular Data Registry
The National Cardiovascular Data Registry (NCDR) is the American College of Cardiology's suite of clinical registries, founded in 1997, holding over 50 million patient records for quality benchmarking.
National Heart, Lung, and Blood Institute
The National Heart, Lung, and Blood Institute (NHLBI) is a US National Institutes of Health institute for research on heart, lung, and blood diseases, created in 1948.
Natriuresis
Natriuresis is renal sodium excretion, governed by tubular reabsorption, pressure natriuresis, and natriuretic peptides; spot urine sodium guides loop diuretic titration in acute heart failure.
Natriuretic peptide
Natriuretic peptides (ANP, BNP, CNP; BNP and NT-proBNP) are heart-derived peptide hormones used as blood biomarkers to diagnose, risk-stratify, and monitor heart failure, with guideline rule-out thresholds and prognostic value.
Navel
Navel (belly button, umbilicus): the fibrous scar left after the umbilical cord detaches, containing obliterated orifices of one vein and two arteries; landmark at T10, prone to hernia, urachal and omphalomesenteric remnant disease.
NCE-G 120
NCE-G 120 (G120, NeuroChirurgie Eppendorf-Glioma 120), CVCL_N742, is a human glioblastoma cancer cell line from a 59-year-old male, left temporo-parietal junction, used in p53, radiation, and transcriptomic studies.
NCE-G 44
NCE-G 44 (G44, GL44; CVCL_N727) is a human glioblastoma cell line from a 64-year-old woman's left parietal lobe, established at University Hospital Hamburg-Eppendorf, with a TP53 p.Glu224Ter mutation and high MGMT-driven temozolomide resistance.
Near-sightedness
Near-sightedness (myopia) is a refractive error in which light focuses in front of the retina, blurring distance vision. Onset is typically ages 6–14; atropine drops, multifocal lenses, and orthokeratology slow childhood progression.
Neck
The neck (cervical spine): seven vertebrae C1–C7, atlas and axis, eight cervical nerves, discs and facet joints, supporting the head, enabling motion, and protecting the spinal cord.
Neil Harbisson
Neil Harbisson is a British-born artist and cyborg activist born with achromatopsia. His antenna implant converts light frequencies into sound, enabling him to hear colors beyond the human spectrum.
Neocortex
Neocortex (isocortex): the six-layered outer cerebral cortex found only in mammals, part of the dorsal pallium, up to about 80% of the human brain, expanded in human prefrontal and language areas.
Neonatal cerebral sinovenous thrombosis
Neonatal cerebral sinovenous thrombosis (CSVT) is venous thrombosis of cerebral veins or dural sinuses in newborns, causing seizures and encephalopathy, with 2.6 to 12 cases per 100,000 term neonates yearly and controversial anticoagulation treatment.
Neonatal hypotension
Neonatal hypotension is abnormally low blood pressure in newborns, mainly preterm infants, affecting about 50% of VLBW babies in the NICU; no standard definition exists, and dopamine, dobutamine, and hydrocortisone are main treatments.
Nephron
Nephron: the kidney's microscopic functional unit, comprising glomerulus, Bowman capsule, proximal tubule, loop of Henle, and distal tubule; performs filtration, reabsorption, and secretion; nephron number links to hypertension and CKD risk.
Nerve block
Nerve block: injection of medication near a nerve or nerve group for pain relief, diagnosis, or surgical anesthesia. Also regional anesthesia; first performed by Halsted with cocaine in 1884; includes epidural, Bier, and peripheral blocks.