Transcript Document
Compensatory Eye Movements John Simpson Functional Classification of Eye Movements Movements that stabilize the eye when the head moves Vestibulo-ocular Uses vestibular input to hold images stable on the retina during brief or rapid head movement Optokinetic Uses visual input to hold images stable on the retina during sustained or slow head movement Movements that keep the fovea on a visual target Saccade Brings new objects of interest onto the fovea Smooth Pursuit Holds the image of a moving target on the fovea Vergence Adjusts the eyes for different viewing distances in depth Cupula and otoliths move sensory receptors Cristae Maculae Angular Acceleration Angular Velocity Angular Position Cupula Deflection Canal afferents respond to cupula motion Canal afferents code velocity • Spontaneous activity allows for bidirectional signaling • S-curve is common • Different cells have different ranges and different dynamics • Population code Cupula and otoliths move sensory receptors Cristae Maculae Classes of eye movements • Reflexive – gaze stabilization – VOR • Stabilize for head movements – Optokinetic • Stabilize for image motion • Voluntary – gaze shifting – Saccades • Acquire stationary target – Smooth pursuit • Acquire moving target – Vergence • Acquire target in depth VOR With and Without Vision rVOR gain varies with frequency • Almost perfect > 1Hz • Low gain for low frequencies (0.1Hz) • Sensory mechanisms can compensate (optokinetic reflex) Optokinetic reflex • Optokinetic nystagmus • Neural pathway (AOS) convergent with VOR Oculomotor muscles and nerves • Oculomotor nerve (III) – Medial rectus – Superior/Inferior recti – Inferior oblique • Trochlear nerve (IV) – Superior oblique • Abducens nerve (VI) – Lateral rectus The 3-Neuron Arc Primary Effects of Canals on Eye Muscles Canal Excites Inhibits Horizontal Ipsi MR, Contra LR Ipsi LR, Contra MR Anterior Ipsi SR, Contra IO Ipsi IR, Contra SO Posterior Ipsi SO, Contra IR Ipsi IO, Contra SR Secondary Effects of Canals on Eye Muscles 19.3 Organization of the cranial nerve nuclei that govern eye movements. 19.7 Synaptic circuitry responsible for horizontal movements of the eyes to the right. Translational VOR • Compensates for change in head position with respect to gravity • Compensates for linear motion as opposed to rotational motion