1,240 articles
Apraclonidine
Apraclonidine (Iopidine) is a selective alpha-2 adrenergic agonist eye drop, a para-amino clonidine derivative approved in 1987 to prevent post-laser IOP spikes and in 1993 for short-term glaucoma therapy; tachyphylaxis limits chronic use.
Aqueous humour
Aqueous humour is the clear fluid filling the eye's anterior and posterior chambers, produced by ciliary processes at 2–3 µL/min, nourishing the avascular cornea and lens, and drained via trabecular and uveoscleral pathways to set intraocular pressure.
Arachnoid cyst
An arachnoid cyst is a benign, fluid-filled sac within the arachnoid layer of the membranes around the brain and spinal cord, filled with cerebrospinal fluid and usually found by accident on imaging.
Arcus senilis
Arcus senilis (corneal arcus, gerontoxon): gray-white lipid ring in the peripheral cornea, common after 50, harmless to vision; premature arcus (arcus juvenilis) flags dyslipidemia and cardiovascular risk.
Arousal
Arousal: physiological and psychological responsiveness state spanning sleep to vigilance, driven by brainstem ascending systems (locus coeruleus, basal forebrain, orexin); distinct from attention and valence, and prerequisite for assessing consciousness.
Astigmatism
Astigmatism is a refractive error in which light focuses at two perpendicular lines in the eye, causing blur. Most common refractive error, about 40% adult prevalence; corrected with cylindrical glasses, toric contact lenses, or surgery.
Astrocyte
Astrocyte: star-shaped glial cell of the CNS, named by Lenhossek in 1891; maintains brain homeostasis by clearing 80% of extracellular glutamate, feeding neurons glutamine, and reacting in disease.
Astrocytoma
Astrocytoma is a glioma that forms in star-shaped astrocyte cells of the brain and spinal cord, graded from slow-growing pilocytic tumors in children to fast-spreading glioblastoma in adults.
Astrocytoma grade 2
Astrocytoma grade 2 (diffuse astrocytoma, IDH-mutant, CNS WHO grade 2) is a slow-growing infiltrative brain glioma defined by IDH1/2 mutation, frequent ATRX/TP53 changes, no 1p/19q codeletion, and few mitoses; treated with surgery, deferred or early radiotherapy, temozolomide, or vorasidenib.
Ataxia
Ataxia is poor muscle control causing clumsy movement, usually from cerebellar damage; it spans hereditary forms (SCAs, Friedreich ataxia, ataxia-telangiectasia), acquired causes, and new drug approvals.
Attention, perception & psychophysics
Attention, Perception, & Psychophysics (AP&P), formerly Perception & Psychophysics (1966–2008), is the Psychonomic Society's peer-reviewed journal for sensory processes, perception, attention, and psychophysics, published by Springer, eight issues yearly, ISSN 1943-3921.
Attic perforation of tympanic membrane
Attic perforation of tympanic membrane (pars flaccida perforation, ICD-11 AB13.1) is a hole in the upper, Shrapnell's membrane segment of the eardrum; an unsafe perforation with elevated risk of cholesteatoma and mastoiditis, usually managed surgically.
Audiology
Audiology: healthcare profession of hearing and balance care; audiologists diagnose and treat hearing, balance, tinnitus, and auditory disorders across all ages; doctoral (Au.D.) trained; shaped by the 2022 FDA OTC hearing aid category.
Auditory cortex
The auditory cortex is the region of the temporal lobe that receives and processes sound information from the ears, with primary area A1 on Heschl's gyrus.
Auditory fatigue
Auditory fatigue is a temporary loss of hearing sensitivity after sound exposure, measured as a temporary threshold shift in decibels that recovers over minutes to days.
Auditory scene analysis
Auditory scene analysis is the framework describing how listeners group a sound mixture into separate auditory streams, established in Albert Bregman's 1990 monograph and the basis of computational sound-separation systems.
Augusto, Michaela, and Lorenzo Odone
Augusto, Michaela, and Lorenzo Odone: the family behind Lorenzo's oil, a 4:1 trioleate/trierucate mixture for adrenoleukodystrophy, the 1992 film, and the Myelin Project.
Aural polyp
Aural polyp (otic polyp, ICD-11 AB1A.0): a polypoid growth in the external ear canal or middle ear, usually inflamed granulation tissue from chronic otitis media or cholesteatoma, presenting with bloody drainage and hearing loss.
Auricle (anatomy)
Auricle (pinna): the visible outer-ear structure of elastic cartilage (lobule is fibrofatty) that funnels sound into the external acoustic meatus; landmarks helix, antihelix, concha, tragus; supplied by superficial temporal and posterior auricular arteries; develops from six hillocks of His.
Autonomic dysreflexia
Autonomic dysreflexia, also called autonomic hyperreflexia, is a life-threatening condition in which a noxious stimulus below a spinal cord injury at or above T6 triggers sudden severe hypertension.
Autonomic nervous system
Autonomic nervous system (ANS): involuntary branch of the peripheral nervous system, divisions sympathetic, parasympathetic, and enteric; term coined by Langley in 1898; regulates heart rate, blood pressure, respiration, digestion.
Autonomic neuron
Autonomic neuron: efferent neuron of the autonomic nervous system, in preganglionic (CNS, cholinergic) and postganglionic (ganglionic, noradrenergic or cholinergic) forms, innervating smooth muscle, cardiac muscle, and glands.
Autosomal dominant childhood-onset proximal spinal muscular atrophy
Autosomal dominant childhood-onset proximal spinal muscular atrophy (SMALED, ORPHA:363447, OMIM 158600) is a rare genetic motor neuron disease with childhood-onset, proximal lower limb weakness, usually static or mildly progressive, caused mainly by DYNC1H1 or BICD2 mutations.
Autosomal dominant drusen
Autosomal dominant drusen (Doyne honeycomb retinal dystrophy, Malattia Leventinese, OMIM 126600) is a rare EFEMP1 R345W macular dystrophy with early-onset radial macular and peripapillary drusen, CNV risk, and anti-VEGF treatment.
Autosomal dominant spastic ataxia type 1
Autosomal dominant spastic ataxia type 1 (SPAX1, OMIM 108600) is a rare hereditary spastic ataxia from VAMP1 variants on 12p13, causing lower-limb spasticity, ataxia, dysarthria, and dysphagia with onset around ages 10 to 20.
Autosomal recessive cerebellar ataxia-epilepsy-intellectual disability syndrome due to RUBCN deficiency
SCAR15, or Salih ataxia (ORPHA:404499, OMIM 615705), is an extremely rare autosomal recessive cerebellar ataxia with epilepsy and intellectual disability caused by biallelic RUBCN variants, including an ancient Saudi founder frameshift mutation.
Autosomal recessive lower motor neuron disease with childhood onset
Autosomal recessive lower motor neuron disease with childhood onset, also DSMA4 (ORPHA:206580, OMIM 611067), is an ultra-rare PLEKHG5-related neuromuscular disease causing childhood proximal and distal weakness progressing to areflexic tetraplegia and respiratory failure.
Axillary nerve
Axillary nerve (circumflex nerve): C5-C6 branch of the posterior cord of the brachial plexus supplying deltoid and teres minor; passes through the quadrangular space; injuries cause shoulder abduction weakness.
Axon
Axon: the single output fiber of a neuron, carrying action potentials from the axon hillock to synaptic terminals; often myelinated with nodes of Ranvier; described by Cajal, who identified the growth cone (1890) and dynamic polarization (1891).
Axon guidance
Axon guidance: how growing axons navigate to targets via growth cone receptors reading attractive and repulsive cues (netrins, Slits, semaphorins, ephrins), Rho GTPase signaling, and roles in disease and regeneration.