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Nigrostriatal pathway
Nigrostriatal pathway: dopaminergic tract from the substantia nigra pars compacta (A9) to the dorsal striatum (caudate and putamen), governing motor control and associative learning; its degeneration causes Parkinson's disease, and it also contributes to reward.
Nipple
Nipple: the central structure of each breast, with about nine milk duct openings, smooth erectile muscle, and hundreds of nerves, surrounded by the areola; types include protruding, flat, and inverted, with polythelia in 2-5% of people.
Nitrendipine
Nitrendipine is a dihydropyridine calcium channel blocker developed by Bayer for hypertension, best known as the first-line drug of the Syst-Eur trial, which showed reduced stroke and dementia rates in older patients.
Nobel Prize in Physiology or Medicine for neuroscience research
Nobel Prizes in Physiology or Medicine have honored neuroscience since 1906, when Golgi and Cajal shared the first, through at least 17 prizes and 40 laureates to 2021.
Nociceptor
A nociceptor, also called a pain receptor, is a sensory neuron that responds to noxious, tissue-damaging stimuli, triggering pain signals in the spinal cord and brain.
Noise-induced hearing loss
Noise-induced hearing loss (NIHL) is permanent or temporary hearing loss from loud impulse sounds or repeated exposure above 85 dBA, damaging cochlear hair cells; preventable, common in workers and teens, with no cure.
Non-invasive and partially invasive brain–computer interfaces
Non-invasive and partially invasive brain–computer interfaces (BCIs) record brain activity without penetrating brain tissue, using scalp EEG or electrodes placed under the skull, as in ECoG and endovascular Stentrode implants.
Non-rapid eye movement sleep
Non-rapid eye movement (NREM) sleep, stages N1–N3, is the non-dream-exclusive phase of sleep marked by slow waves and spindles, deep slow-wave sleep, memory consolidation, and cycles alternating with REM every 80–100 minutes.
Non-spiking neuron
Non-spiking neuron: a neuron signaling with graded, analog membrane potentials instead of action potentials, as in retinal rods, cones, horizontal and bipolar cells, and many invertebrate interneurons; graded synapses release transmitter continuously with ribbon zones and L-type Ca2+ channels.
Non-tuberculous mycobacterial lymphadenitis
Non-tuberculous mycobacterial lymphadenitis (NTM cervicofacial lymphadenitis, scrofula-like adenitis): chronic painless neck node infection in children 1-5, mainly MAC and M. lentiflavum; complete excision cures 98% but risks facial palsy.
Noncardiac influences on heart rate
Noncardiac influences on heart rate are systemic and environmental factors, including body temperature, sleep, posture, altitude, emotion, and caffeine, that change heart rate without any fault in the heart itself.
Noncompaction cardiomyopathy
Noncompaction cardiomyopathy (left ventricular noncompaction, LVNC, hypertrabeculation) is a spongy-myocardium condition with prominent trabeculae and deep recesses; diagnosed by NC/C ratios on echo or CMR, genetically overlapping other cardiomyopathies, with outcomes similar to dilated cardiomyopathy.
Nonproliferative diabetic retinopathy
Nonproliferative diabetic retinopathy (NPDR) is the early stage of diabetic retinopathy, marked by microaneurysms, hemorrhages, exudates, IRMA, and venous beading without neovascularization, staged mild, moderate, or severe.
Nonsynaptic plasticity
Nonsynaptic plasticity: activity- or learning-induced changes in neuronal intrinsic excitability, ion channels, myelin, and homeostatic or metaplastic mechanisms, rather than synaptic strength; includes intrinsic plasticity, slow AHP reductions, and transient excitability-based memory traces.
Noradrenergic neuron
A noradrenergic neuron is a neuron that synthesizes and releases norepinephrine (noradrenaline), a neurotransmitter governing arousal, attention, and stress; the largest cluster sits in the brainstem's locus coeruleus.
Norwood procedure
Norwood procedure: first-stage surgery of three-stage palliation for hypoplastic left heart syndrome, rebuilding the aorta and shunting blood to the lungs via Blalock-Taussig or Sano shunt; neonatal mortality about 15%, five-year survival about 70%.
Nose
The nose is the midline facial organ for breathing and smell. Key facts: three turbinate pairs, nasal cycle of 0.5–6 hours, internal nasal valve 0.73 cm², about 500 human odor receptor types, Kiesselbach's plexus bleeding site.
NR082 (NFS-01, ND4 AAV gene therapy)
NR082 (NFS-01, esonadogene imvoparvovec) is Neurophth's rAAV2-ND4 intravitreal gene therapy for ND4-mutation Leber hereditary optic neuropathy, first trialed in Wuhan in 2011 and in phase 3 GOLD and sham-controlled trials.
NSS study
NSS study (Northern Shanghai Study, NCT02368938): prospective community cohort of elderly Chinese in northern Shanghai, run by Shanghai Tenth People's Hospital, studying cardiovascular risk factors, target organ damage, vascular aging, and mortality.
Nuclear bag fiber
Nuclear bag fibers are the large intrafusal muscle fibers of the muscle spindle, with nuclei clumped in an equatorial bag; they comprise dynamic bag1 and static bag2 types serving velocity and length sensitivity.
Nuclear Events (kinase and transcription factor activation)
Nuclear Events (kinase and transcription factor activation), Reactome pathway R-HSA-198725: human neurotrophin/NTRK1 signaling in which MAPK-family kinases phosphorylate nuclear transcription factors such as CREB1 and ELK1, inducing immediate-early and delayed-early genes.
Nucleus accumbens
Nucleus accumbens (NAc, NAcc), ventral striatum region with core, shell, and rostral pole subdivisions; GABAergic MSNs receiving VTA dopamine and prefrontal glutamate; central to reward, motivation, addiction relapse, and DBS targets.
Nutcracker syndrome
Nutcracker syndrome: symptomatic compression of the left renal vein between the aorta and superior mesenteric artery, causing hematuria, flank pain, and proteinuria; treated conservatively or by LRV transposition, stenting, or autotransplantation.
NUZ-001 (monepantel)
NUZ-001 is the clinical code for (S)-monepantel, a veterinary anthelmintic repurposed by Neurizon Therapeutics as an investigational amyotrophic lateral sclerosis drug, now in Phase 2/3 testing.
Nystagmus
Nystagmus: involuntary rhythmic eye movement with slow and fast phases, classified as infantile (congenital) or acquired. Causes include albinism, FRMD7 mutation, retinal disease, and brainstem or cerebellar lesions.
Obstruction of Eustachian tube
Obstruction of the Eustachian tube (ICD-10 H68.1), obstructive or dilatory Eustachian tube dysfunction: failure of tubal opening causing middle-ear pressure dysregulation; treated medically or by balloon dilation with about 1.4% complication rate.
Obstructive shock
Obstructive shock: circulatory shock from mechanical blockage of blood flow into or out of the heart, mainly pulmonary embolism, tension pneumothorax, and cardiac tamponade; about 2% of shock cases, treated by relieving the obstruction.
Occipital bone
Occipital bone (os occipitale): the unpaired skull bone forming the back and base of the cranium around the foramen magnum. Four parts (basilar, two condylar, squamous); articulates with parietals, temporals, sphenoid, atlas; dual endochondral and intramembranous ossification from week 8-9.
Occipital bun
Occipital bun (chignon): a posterior projection of the occipital squama characteristic of Neanderthals, present in 93.3% of sampled European Neandertals; a weaker 'hemibun' occurs in some modern humans and is likely not homologous.
Occipital lobe
Occipital lobe: smallest, rearmost cerebral lobe, housing the primary visual cortex (V1, calcarine sulcus) and dorsal/ventral visual streams; supplied by the posterior cerebral artery; damage causes homonymous field loss and cortical blindness.