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- J waveAbnormal electrocardiogram finding
- James BorthwickScottish surgeon
- Jamming avoidance responseBehavior of some weakly electric fishes
- Janellen HuttenlocherAmerican psychologist (1932–2016)
- Jaw jerk reflexStretch reflex of trigeminal nerve
- Jean SteinJean Babette Stein (February 9, 1934 – April 30, 2017) was an American author and editor.
- Jean-Baptiste Marc BourgeryFrench physician and anatomist
- Jean-Pierre ChangeuxFrench neuroscientist (born 1936)
- JenkemPurported inhalant drug
- Jervell and Lange-Nielsen syndromeMedical condition
- Johann Christian ReilJohann Christian Reil (20 February 1759 – 22 November 1813) was a German physician, physio
- John MollonBritish scientist
- John Newsom-DavisJohn Michael Newsom-Davis (18 October 1932 – 24 August 2007) was a neurologist who played
- John O'Keefe (neuroscientist)American–Irish neuroscientist
- John T. CacioppoAmerican academic
- Joint capsuleIn anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joi
- Journal of Clinical NeurophysiologyThe Journal of Clinical Neurophysiology is a bimonthly peer-reviewed medical journal cover
- Jugular foramenOpening in the base of the skull allowing many structures to pass
- Jugular veinVeins that bring deoxygenated blood from the head back to the heart
- Junctional ectopic tachycardiaIrregular heartbeat due to abnormal conduction from the atrioventricular nerve
- Junctional epitheliumArea of gum tissue which attaches to the base of a tooth
- Junctional escape beatMedical condition
- Junctional rhythmMedical condition
- Junctional tachycardiaAbnormally fast heartbeat, the cause of which involves the atrioventricular node
- Juncturae tendinumConnective tissues linking the tendons which extend the fingers
- Jürgen AschoffGerman physician, biologist and behavioral physiologist
- Juxtaglomerular apparatusStructure that regulates function of each nephron