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Basal ganglia
Basal ganglia (basal nuclei): interconnected subcortical brain nuclei (caudate, putamen, globus pallidus, subthalamic nucleus, substantia nigra) that modulate voluntary movement via direct and indirect striatal pathways; dysfunction causes Parkinson disease, Huntington disease, and dystonia.
Basilar artery
Basilar artery: unpaired brain artery formed by union of the vertebral arteries at the pontomedullary junction, ascending on the pons and ending as the posterior cerebral arteries; supplies brainstem, cerebellum, and occipital lobes.
Basilar membrane
Basilar membrane: elastic membrane dividing the cochlea's scala media and scala tympani, carrying the tonotopic traveling wave discovered by von Békésy (Nobel 1961), later shown to be nonlinear and amplified by outer hair cells.
Basilic vein
Basilic vein (vena basilica): large superficial vein of the arm, arising from the ulnar dorsal venous network, joining the brachial veins to form the axillary vein; preferred site for PICC and midline catheters and used for hemodialysis fistulas.
Basket cell
Basket cell: GABAergic inhibitory interneuron forming basket-like axon terminals around pyramidal cell somata and proximal dendrites; two classes, fast-spiking parvalbumin and regular-spiking CCK basket cells, controlling principal cell output and oscillations.
Bates method
Bates method: alternative vision-improvement system by ophthalmologist William H. Bates (Perfect Sight Without Glasses, 1920), using palming, sunning, swinging, and central fixation; rejected by ophthalmology, trials show no refractive improvement, and sungazing risks solar retinopathy.
Batten disease
Batten disease, also called Spielmeyer-Vogt disease or Batten-Mayou syndrome, is the common name for the neuronal ceroid lipofuscinoses, inherited lysosomal storage disorders causing childhood vision loss, seizures, and early death.
Beard
Beard: androgen-driven terminal facial hair of men, grown from puberty. Covers biology, minoxidil beard trials, pseudofolliculitis barbae, bacterial colonization and shedding evidence in surgeons, and beard history.
Beauty mark
Beauty mark: cultural term for an attractive small facial mole, medically a nevus (melanocytic nevus). Includes artificial mouches worn in 17th-18th century Europe and Marilyn Monroe's 1950s icon; ABCDE rule flags dangerous change.
Beck's triad (cardiology)
Beck's triad: hypotension, elevated jugular venous pressure, and muffled heart sounds described by Claude Beck in 1935, the classic but insensitive bedside sign of acute cardiac tamponade.
Behavioral neuroscience
Behavioral neuroscience, also known as biological psychology or biopsychology, is the branch of neuroscience studying how the nervous system produces behavior, emotions, and mental processes, largely through experiments with laboratory animals.
Belching
Belching, also called eructation or burping, is the audible escape of air from the esophagus or stomach into the pharynx, usually normal but a disorder when excessive.
Bell's palsy
Bell's palsy, or idiopathic facial nerve palsy, is sudden one-sided facial weakness, the most common cause of facial paralysis; steroids within 72 hours help, and most patients recover within 3 to 6 months.
Benign neoplasm of tonsil
Benign neoplasm of tonsil (ICD-11 2E90.4, ICD-10 D10.4): rare non-malignant tonsillar tumors, most commonly squamous papilloma; diagnosed histologically, treated by surgical excision.
Benign vascular tumors of the spleen
Benign vascular tumors of the spleen are noncancerous masses arising from splenic blood vessels, including hemangioma, hamartoma, lymphangioma, and the rare SANT, first reported in 2004.
Bepridil
Bepridil is a long-acting calcium channel blocker with anti-arrhythmic activity, approved in 1990 for angina and hypertension, withdrawn in the United States for causing torsade de pointes.
Bernheim syndrome
Bernheim syndrome: proposed right ventricular compression by a hypertrophied septum causing right heart failure without lung congestion, described by Hippolyte Bernheim in 1910 and now considered a doubtful entity.
Beta Rhythm
Beta rhythm: EEG brain waves of 15–30 Hz (often 13–30 Hz) seen during wakefulness and mental activity; named by Hans Berger in 1930, low amplitude (10–20 µV), frontal-central, enhanced by sedatives.
Beta-1 adrenergic receptor
Beta-1 adrenergic receptor (ADRB1), a cardiac Gs-coupled GPCR activated by norepinephrine; target of beta-1 selective blockers like metoprolol and bisoprolol; gene on chromosome 10q24-q26.
Betz cell
Betz cell, giant pyramidal neuron (Riesenpyramide) of layer Vb of the primary motor cortex, described by Volodymyr Betz in 1874; largest cortical neurons, projecting via the corticospinal tract, monosynaptic to spinal motoneurons in primates, absent in rodents, and implicated in ALS.
Bezold–Jarisch reflex
Bezold–Jarisch reflex (BJR): cardioinhibitory reflex from left ventricular inferoposterior receptors via vagal C fibers causing bradycardia, vasodilation, hypotension; key in spinal anesthesia asystole, vasovagal syncope, inferior MI.
Biceps
Biceps (biceps brachii) is the two-headed upper-arm muscle flexing the elbow and supinating the forearm, innervated by the musculocutaneous nerve (C5-C6), inserting on the radial tuberosity, and highly variable, with accessory heads in 2-5% of people.
Biceps femoris muscle
Biceps femoris (Musculus biceps femoris), the most lateral hamstring muscle of the posterior thigh, has long and short heads with different origins and innervation (tibial vs common fibular divisions of the sciatic nerve) sharing insertion on the fibular head; it extends the hip, flexes the knee, and is the most commonly injured hamstring.
Bicuculline
Bicuculline is a plant-derived alkaloid isolated in 1933 from Dutchman's breeches that competitively blocks GABAA receptors; a powerful convulsant, it has been the standard pharmacological tool for studying GABA-mediated inhibition since 1970.
Bietti crystalline dystrophy
Bietti crystalline dystrophy (BCD, Bietti crystalline corneoretinal dystrophy) is a rare autosomal recessive retinal disease caused by CYP4V2 mutations, marked by yellow-white retinal crystals, night blindness, and progressive vision loss.
Bifascicular block
Bifascicular block, also called bifascicular heart block, is an ECG conduction disorder affecting two of three His-Purkinje fascicles (RBBB plus LAFB or LPFB, or LBBB), risking complete AV block, syncope, and pacemaker decisions.
Bigeminy
Bigeminy: a heart rhythm in which every normal beat is followed by a premature ectopic beat, atrial or ventricular. Also called bigeminal rhythm. Causes include heart disease, stimulants and electrolyte imbalance; diagnosed by ECG and Holter; ablation succeeds in 75% or more of cases.
Bile
Bile (gall) is the yellowish-green digestive fluid made by the liver (800–1,000 mL/day), stored in the gallbladder, and released into the duodenum; its bile salts emulsify fats, carry bilirubin out, and recycle via enterohepatic circulation, while bile acids signal through FXR and TGR5.
Bile duct
Bile ducts are the tubular channels that carry bile from the liver to the gallbladder and small intestine; their main trunk is the common bile duct, about 10 cm long, whose obstruction can cause cholangitis or cholangiocarcinoma.
Binaural hearing
Binaural hearing is the brain's use of input from both ears to locate sounds in space, based on differences in arrival time and intensity between the ears.