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Friedreich's ataxia
Friedreich's ataxia (FRDA) is an autosomal recessive ataxia from GAA repeat expansion in FXN causing frataxin deficiency; features gait ataxia, areflexia, cardiomyopathy, diabetes; omaveloxolone (Skyclarys) is the first approved drug.
Frontal lobe
Frontal lobe: anterior lobe of each cerebral hemisphere containing primary motor cortex, Broca's area, and prefrontal cortex; supports movement, expressive language, and divided prefrontal functions, not disproportionately enlarged in humans versus apes.
Frontal lobe disorder
Frontal lobe disorder, often called frontal lobe syndrome, is an impairment of brain function from damage to the frontal lobes, causing disinhibition, personality change, and impaired judgment.
Functional magnetic resonance imaging
Functional magnetic resonance imaging (fMRI), including BOLD task fMRI and resting-state fMRI, noninvasively maps brain activity via blood oxygenation; developed from Ogawa's 1990 BOLD discovery, used clinically for presurgical planning, with known poor task-fMRI test-retest reliability (mean ICC .397).
Functional near-infrared spectroscopy
Functional near-infrared spectroscopy (fNIRS), also called optical topography or diffuse optical imaging, is a portable, non-invasive neuroimaging method using 650–950 nm light to measure cortical HbO/HbR hemodynamic changes; first human studies 1991/1992, standardized by IEC 80601-2-71:2025.
Functional neuroimaging
Functional neuroimaging measures human brain activity via fMRI, PET, MEG, EEG, and fNIRS, either hemodynamically (millimeter spatial, seconds temporal) or electromagnetically (millisecond temporal), with clinical use in presurgical brain mapping.
Functional parkinsonism
Functional parkinsonism (FP), ICD-11 8A00.3, is a parkinsonian syndrome caused by functional neurological disorder, not dopamine degeneration; tremor, rigidity, and slowness show distractibility, entrainment, and no true bradykinesia.
Functional Residual Capacity
Functional residual capacity (FRC): lung gas volume after normal passive exhalation, ERV plus RV, about 3 L normally. Measured by plethysmography, helium dilution, or nitrogen washout, not spirometry; rises in obstruction, falls in obesity and anesthesia.
Fungal keratitis
Fungal keratitis (mycotic keratitis, keratomycosis) is a fungal cornea infection causing blindness and eye loss, mainly from Fusarium, Aspergillus, and Candida after trauma or contact lens wear; treated with topical natamycin.
G-spot
G-spot (Gräfenberg spot): a putative erogenous area on the anterior vaginal wall, named after Ernst Gräfenberg. Systematic reviews find no agreed anatomical structure; existence, location, and nature remain unproved.
GABAergic interneuron
GABAergic interneuron: local inhibitory neuron using GABA as neurotransmitter, also called GABAergic inhibitory interneuron. Three cortical groups (PV ~40%, SST ~30%, 5HT3aR ~30%) arise from the ganglionic eminence and regulate circuit timing.
GABRB3
GABRB3, also called ECA5/DEE43, is a human gene at 15q12 encoding the beta3 subunit of the GABA_A inhibitory chloride-channel receptor. Pathogenic variants split into gain- and loss-of-function groups causing distinct epileptic encephalopathies; reduced expression marks Angelman and Prader-Willi syndromes.
Gait
Gait: the pattern of human or animal walking and running, analyzed via the gait cycle (60% stance, 40% swing). Also called locomotion analysis; measured by observational, 3D laboratory, wearable IMU, and video methods.
Gallamine
Gallamine, marketed as the triethiodide salt Flaxedil, is a synthetic non-depolarizing neuromuscular blocking agent introduced in 1946 to relax skeletal muscle during general anesthesia, withdrawn after causing pronounced tachycardia.
Gallbladder
Gallbladder: pear-shaped bile-storage organ under the liver, 7-10 cm, holding 30-50 mL bile released via CCK. Gallstones affect 10-15% of Americans; removal (cholecystectomy) is common and survivable.
Gamma motor neuron
A gamma motor neuron, also called a fusimotor neuron, is a lower motor neuron of the spinal cord or brainstem that innervates muscle spindle intrafusal fibers and regulates spindle sensitivity.
Gamma wave
Gamma wave: brain rhythm in the gamma band, roughly 30–90 Hz (definitions vary to 30–150 Hz), first named by Jasper and Andrews in 1938; generated by pyramidal cell–parvalbumin interneuron interactions, linked to attention, memory, and Alzheimer's research.
Gamut
Gamut: the subset of colors a device or color space (sRGB, Display P3, Rec. 2020) can represent; measured as coverage of a chromaticity triangle, distinct from color volume and accuracy.
Ganglionic eminence
The ganglionic eminence is a transient embryonic structure in the ventral telencephalon that produces the basal ganglia's neurons and most inhibitory interneurons of the cortex and hippocampus.
Gangrene
Gangrene: death of body tissue from blocked blood supply (ischemia), bacterial infection, or both; types include dry, wet, and gas gangrene (Clostridium). Major risk factors are diabetes and peripheral arterial disease; treatment is debridement, antibiotics, and revascularization.
Gap junction
A gap junction, also known as a communicating junction or macula communicans, is a cluster of intercellular channels that lets ions and small molecules pass between cells.
Gastric acid
Gastric acid, or stomach acid, is the hydrochloric acid secreted by parietal cells of the stomach lining, keeping stomach pH near 1.5 to digest protein and kill microbes.
Gastric Emptying
Gastric emptying, the evacuation of food from the stomach into the duodenum, normally takes about 4 hours for 90% of a meal. Measured by scintigraphy (reference standard), 13C breath test, or wireless motility capsule to diagnose gastroparesis or dumping syndrome.
Gastric lymph nodes
Gastric lymph nodes drain the stomach and are numbered as stations 1–16+ in the Japanese Classification of Gastric Carcinoma, defining D1/D2 lymphadenectomy levels and N staging for gastric cancer.
Gastrin
Gastrin is a peptide hormone, the second hormone discovered (Edkins, 1905), produced by gastric antrum G cells. It stimulates gastric acid via the CCK2 receptor and ECL-cell histamine; elevated in Zollinger-Ellison syndrome, H. pylori infection, and PPI use.
Gastrocnemius muscle
Gastrocnemius (musculus gastrocnemius), the superficial two-headed calf muscle; with soleus and plantaris forms the triceps surae. Plantar flexes the ankle, flexes the knee, inserts via the Achilles tendon, innervated by the tibial nerve (S1, S2).
Gastrointestinal tract
Gastrointestinal tract (GI tract, digestive tract, alimentary canal): the tube from mouth to anus, mouth, esophagus, stomach, small and large intestine, that digests food, absorbs nutrients, and eliminates waste, aided by liver, pancreas, gallbladder.
Gaucher's disease
Gaucher's disease (Gaucher disease) is a rare autosomal recessive lysosomal storage disorder caused by GBA1 variants and glucocerebrosidase deficiency, with types 1, 2, and 3, treated by enzyme replacement or substrate reduction therapy.
Geert W. Schmid-Schoenbein
Geert W. Schmid-Schoenbein is a German-born American bioengineer, Distinguished Professor at UC San Diego, known for microcirculation research and the autodigestion hypothesis of shock injury.
Gene therapy of the human retina
Gene therapy of the human retina: AAV-mediated delivery of therapeutic genes to treat inherited retinal diseases and neovascular disorders. Luxturna (voretigene neparvovec, 2017) is the first approved product, for biallelic RPE65 retinal dystrophy.