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Lecture 8

Lecture 8.docx

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University of Toronto Scarborough
Matthias Niemeier

Lecture 8 Posture and gaze control SAQ 1. What is direct feedback and what is internal feedback? 2. How is feedback different from feedforward? Overview 1. Posture a. Contributions from pressure receptors b. Vestibular contributions c. Visual contributions d. Interactions e. Synopsis 2. Eye movements Contributions from pressure receptors 1. Support area a. Center of gravity b. Small support area in humans c. Pressure receptors 2. Responses to pressure distribution a. Tonic response i. Positive supporting reaction b. Transient component i. Extensor thrust c. Stepping reaction if COG outside critical area Vestibular contributions 1. Static vestibular reactions a. Otolith organs i. Absolute head position in space 1. Head righting reflex 2. Static vestibulo-ocular reflex 3. Tonic postural vestibular reflexes 2. Dynamic vestibular reaction a. Semicircular canals velocity sensitive i. Respond more quickly b. VOR i. Phases 1. Quick 2. Slow c. Postural vestibular reflexes Visual contributions 1. Visual cues about upright 2. Dynamic responses a. Optic flow i. OKN 3. Eye in head signals a. Efference copy Interactions 1. Vestibular lesions a. Imbalanced push-pull b. False sense of rotations c. Recalibration with vision 2. Motion sickness 3. Proprioceptive neck reflexes a. Complementary to vestibular neck reflex i.  Any head position possible 1. E.g. a. Vestibular i. Head down  Front legs extend b. Propriception i. Dorsiflexion  Front legs extend Synopsis 1. Eye in visual space (+) / Eye related to head (-) a. Retina / Oculomotor system 2. Head in visual space (+) / Head in inertial space (+) a. Retino-Oculomotor / Vestibular system 3. Head in space (+) / Head relative to body (-) a. Retino-Oculomotor-Vestibular / Neck joint receptors 4. Body in space (+) / Body in space (+) a. Retino-Oculomotor-Vestibular-Neck / Pressure receptors 5. Postural commands a. Receives anticipatory feed forward innervation 6. Postural adjustment 7. M. Spindles Overview 1. Posture 2. Eye movements a. Six kinds of eye movements b. Six eye muscles c. Eye movements are three dimensional d. The motor circuits for the saccades lie in the brain stem e. Cerebral control of saccades f. Smooth pursuit and vergence g. Eye-head coordination Six kinds of eye movements 1. Bring fovea to target and keep it there a. Saccades and fixations i. Move fovea to target ii. Up to 900 degrees / second iii. Saccade amplitude under voluntary control, not velocity b. Smooth pursuit c. Requires moving stimulus d. Vestibulo ocular reflex e. Sawtooth pattern f. Optokinetic nystagmus g. Vergence movements h. Linked with accommodation i. Near response 2. Six eye muscles 1. 3 axes of rotation 2. Each eye has 3 pairs of agonist / antagonist muscles 3. This allows rotations about any axis in 3 dimensions a. Turning eye i. Right or left ii. Up or down iii. Clockwise or counter clockwise 4. Muscles a. Lateral rectus / medial rectus b. Superior rectus / inferior rectus c. Superior / inferior oblique 5. Horizontal eye movements a. Lateral rectus (abduction) b. Medial rectus (adduction) 6. Vertical and torsional eye movements a. More complicated abduction and adduction b. Table (slide 28) 7. Eye muscles are controlled by 3 cranial nerves a. Abducens (VI) i. Lateral rectus b. Trochlear (IV) i. Superior oblique c. Oculomotor (III) i. Other 4 muscles 8. Problems with eye muscle control can be a serious warning sign a. Double vision b. Lesions can be localized based on symptoms i. E.g. lesion of the trochlear nerve results in deficits in intorsion and depression Eye movements are 3D 1. 2D problem a. To point the fovea at a target requires certain amount of vertical and horizontal rotation i. Free choice of final positions ii. Donders' law
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