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Binocular rivalry
Binocular rivalry: alternating conscious perception when two different images are shown one to each eye. Also called ocular equivocation; first systematically studied by Wheatstone (1838); key paradigm for consciousness research and interocular suppression.
Binocular vision
Binocular vision, also called binocular fusion, is the use of both eyes together so the brain merges two slightly different retinal images into a single percept with depth.
Biocompatibility
Biocompatibility: the ability of a medical device or material to perform with an appropriate host response in a specific application. Evaluated under ISO 10993-1 and FDA guidance via risk assessment and cytotoxicity, irritation, sensitization, and other endpoint testing.
Biological psychiatry
Biological psychiatry: interdisciplinary science of the biological bases of behavior (biochemical, genetic, physiological, neurological) applied to mental illness; three historical waves, flagship journal Biological Psychiatry (1969), ongoing biomarker and clinical-translation debate.
Bioprosthesis
Bioprosthesis: an implant, usually a heart valve, made of biological tissue (porcine, bovine pericardial, homograft) stabilized with glutaraldehyde; avoids lifelong anticoagulation but degenerates, needing reoperation more often than mechanical valves.
Bipolar neuron
Bipolar neuron: a nerve cell with one axon and one dendrite extending from opposite poles of the soma; rare sensory neurons of the retina, olfactory epithelium, and inner-ear ganglia.
Birthmark
Birthmark: a colored or raised skin mark present at birth or shortly after, in vascular (salmon patch, hemangioma, port-wine stain) and pigmented (cafe-au-lait spot, congenital nevus, dermal melanocytosis) types, mostly benign but some signaling syndromes or melanoma risk.
Bite Force
Bite force, or occlusal force, is the force exerted by the jaw muscles on teeth, measured in newtons; healthy adults reach 300-600 N in the molar region, with male, posterior, and bilateral values higher.
Bitemporal hemianopsia
Bitemporal hemianopsia (bitemporal hemianopia): loss of the temporal half of the visual field in both eyes, classically from a pituitary adenoma or other lesion compressing crossing nasal fibers at the optic chiasm.
Black eye
Black eye (periorbital hematoma, periorbital ecchymosis): bruising and swelling around the eye from face or head trauma, usually healing in days to 3 weeks; ice, acetaminophen, and checks for hyphema, orbital fracture, or skull fracture.
Black hair
Black hair, human hair with abundant eumelanin pigment, the darkest and most common hair color worldwide (over 90% brown or black); controlled polygenically, with MC1R the best-studied gene.
Bladder
Bladder (urinary bladder): hollow pelvic muscular organ storing 300-500 mL of urine in humans; detrusor wall, urothelium lining, trigone base; sympathetic storage, parasympathetic voiding; disorders include incontinence and urothelial cancer.
Blalock–Thomas–Taussig shunt
Blalock–Thomas–Taussig shunt (modified BTT shunt, mBTS): palliative systemic-to-pulmonary artery connection for cyanotic congenital heart disease, first performed by Blalock, Thomas, and Taussig at Johns Hopkins on November 29, 1944; modern form uses a PTFE graft.
Bleeding
Bleeding (hemorrhage) is blood loss from damaged vessels, arrested by hemostasis or by pressure, tourniquets, surgery, and transfusion; over 90% of pre-facility trauma deaths are from hemorrhage.
Blepharoplasty
Blepharoplasty, or eyelid surgery, removes or repositions excess eyelid skin, muscle, and fat for cosmetic or functional reasons. Named by von Graefe in 1818; origins with Susruta; first double-eyelid surgery by Mikamo Nagai in 1896.
Blepharospasm
Blepharospasm, or benign essential blepharospasm, is an adult-onset focal dystonia causing involuntary orbicularis oculi spasms and forced eyelid closure; treated mainly with botulinum toxin injections every 3 to 4 months, with myectomy for refractory cases.
Blind spot (vision)
Blind spot (vision), or physiological blind spot (punctum caecum), is the visual-field gap corresponding to the photoreceptor-free optic disc, about 6° × 7° at 15–16° temporal; discovered by Mariotte in 1668 and normally hidden by filling-in and the fellow eye.
Blindsight
Blindsight: residual visual capacity, such as detecting or locating stimuli, without perceptual awareness after primary visual cortex (V1) damage; coined by Larry Weiskrantz from patient DB studies, supported by LGN and superior colliculus-pulvinar pathways.
Blinking
Blinking: rapid eyelid closing and opening in spontaneous, reflex, and voluntary forms, spreading the tear film at 8–21 blinks per minute, controlled by brainstem and cortical circuits, and modulated by dopamine.
Blond
Blond (blonde) hair: low-eumelanin human hair color common in northern Europe (polygenic, KITLG enhancer and 200+ variants) and independently in Melanesia via a recessive TYRP1 93C allele at 26% frequency, absent outside Oceania.
Blood
Blood: specialized circulating body fluid of plasma, red blood cells, white blood cells, and platelets; about 55% plasma, carries oxygen, fights infection, clots; types A, B, AB, O with Rh factor.
Blood Flow Velocity
Blood flow velocity is the speed of blood in vessels (cm/s or m/s), measured mainly by Doppler ultrasound; flow = velocity × cross-sectional area. Key uses: stenosis grading, transcranial Doppler thresholds (vasospasm 180 cm/s, sickle cell 200 cm/s), angle-dependent errors.
Blood pressure
Blood pressure is the force of blood against artery walls, reported as systolic/diastolic in mm Hg; normal is under 120/80, high at 130/80 or above, measured by cuff methods and confirmed with ambulatory or home monitoring.
Blood sugar regulation
Blood sugar regulation: hormonal control of blood glucose by pancreatic insulin (lowering) and glucagon (raising), plus incretins, counterregulation, A1C and CGM monitoring, and diabetes treatment.
Blood type
Blood type: classification of blood by ABO group (A, B, AB, O) and RhD status, discovered by Karl Landsteiner in 1901; determines transfusion compatibility, with O negative the universal red cell donor and 49 ISBT-recognized systems by 2026.
Blood vessel
Blood vessels are the arteries, veins, and capillaries that carry blood through the body in pulmonary and systemic circuits; about 60,000 miles total, with three-layered walls, venous valves, and roughly 70 percent of blood volume held in veins.
Blood Viscosity
Blood viscosity, the internal resistance of whole blood to flow, is non-Newtonian and shear-thinning, governed by hematocrit, plasma fibrinogen, and red cell aggregation and deformability; it marks cardiovascular, hematological, and inflammatory risk.
Blood volume
Blood volume, also called volemia, is the total amount of blood circulating in the arteries, capillaries, veins, and heart, about 5 liters in an average adult, varying with body size.
Blood–brain barrier
Blood–brain barrier (BBB): selective endothelial interface of brain capillaries with tight junctions and efflux pumps; blocks over 90% of small-molecule drugs; crossed via GLUT-1, receptor-mediated transcytosis (TfR1, LRP1), or focused ultrasound opening; term coined by Lewandowsky in 1900.
Blue Brain Project
Blue Brain Project: Swiss EPFL brain-simulation initiative led by Henry Markram, 2005–2024, using IBM and HPE supercomputers to digitally reconstruct rat and mouse neocortical microcircuits, culminating in the 2015 31,000-neuron reconstruction and a whole mouse brain model.