Joint Position Sense: Population Coding by Articular Mechanoreceptors

Knowing your knee angle without looking at it depends on a ring of stretch-sensitive mechanoreceptors embedded in the joint capsule and ligaments, each broadly tuned to fire most strongly near one particular angle across the joint's range of motion. This simulation renders a 3D hinge joint surrounded by a population of these Ruffini/Pacinian-type afferents, each with its own Gaussian tuning curve, and decodes the population's combined firing pattern into a single joint-angle estimate using vector-average population coding — the same read-out strategy the nervous system relies on. Drag the flexion slider to move the joint and watch each receptor's bar respond to its own tuning curve, add afferent noise or remove receptors to see position sense degrade the way it does after joint injury or peripheral neuropathy, and compare the live population estimate against the true angle.