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Eye Movements

Dive into the intricate world of eye movements as we unravel the oculomotor plant, neural constraints, gaze behaviors, motor neurons, VOR dynamics, and more. Understand the mechanisms behind reflexive and voluntary eye movements, gaze holding, shifting, and vergence. Delve into the fascinating interplay between the oculomotor muscles, nerves, and sensory mechanisms that govern our eyes' intricate motions.

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Eye Movements

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  1. Eye Movements

  2. 1. The Plant

  3. The Oculomotor Plant Consists Of only 6 muscles in 3 pairs

  4. This Yields 3 degrees of Mechanical Freedom

  5. Donder’s Law/ Listing’s Law Neural Constraints Reduce this to 2 degrees of freedom

  6. 3-D eye movements • Donder’s Law • Relates torsion to eye position • Listing’s law • Torsion results from rotation of eye around perpendicular axis • Listing’s plane • Plane orthogonal to line of sight • Does not apply when head is free

  7. Kinematics vs Dynamics In the Oculomotor System Rotations about the Center of Gravity No Loads No Inertia Force = Position

  8. Oculomotor muscles and nerves • Oculomotor nerve (III) • Medial rectus • Superior/Inferior recti • Inferior oblique • Trochlear nerve (IV) • Superior oblique • Abducens nerve (VI) • Lateral rectus • Medial longitudinal fasciculus

  9. 2. The Behaviors Gaze Holding: VOR OKN Gaze Shifting: Saccades Vergence Smooth Pursuit

  10. 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

  11. Gaze During Nystagmus

  12. Saccades

  13. 3-D Gaze Trajectory Vergence

  14. 2. The Motor Neurons

  15. Force Patterns Robinson’s Lollipop Experiments Statics Dynamics

  16. Oculomotor Neurons During Static Gaze

  17. Dynamics and Statics

  18. 3. VOR

  19. Cupula and otoliths move sensory receptors Cristae Maculae

  20. Angular Acceleration Angular Velocity Angular Position Cupula Deflection

  21. Canal afferents code velocity • Spontaneous activity allows for bidirectional signaling • S-curve is common • Different cells have different ranges and different dynamics • Population code

  22. Canal Output During Slow Sinusoidal Rotation

  23. VOR With and Without Vision

  24. rVOR gain varies with frequency • Almost perfect > 1Hz • Low gain for low frequencies (0.1Hz) • Sensory mechanisms can compensate (optokinetic reflex)

  25. Oculomotor muscles and nerves • Oculomotor nerve (III) • Medial rectus • Superior/Inferior recti • Inferior oblique • Trochlear nerve (IV) • Superior oblique • Abducens nerve (VI) • Lateral rectus

  26. The 3-Neuron ArcPrimary 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

  27. Robinson’s Model of the VOR

  28. Robinson

  29. 4. OKN

  30. Type I Vestib Neuron

  31. Bode Plot of OKN

  32. Bode Plot of VOR

  33. Bode Plot of OKN

  34. 5. Saccades

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