Motor Control- Vision Eye Movements

Motor Control- Vision Eye Movements - Sensory Systems...

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Unformatted text preview: Sensory Systems Involved in Sensory Systems Involved in Motor Control Sensory Physiology Sensory Physiology There are different sensory receptors for each of the senses. 3 things in common: ­Respond to physical stimulus (light energy, sound waves, etc.) ­Convert stimulus to AP’s ­Give information to CNS so that you can perceive that sensation Sensation vs. Perception Visual Physiology Visual Physiology 1. Light enters eye and is focused by lens onto retina. 2. Photoreceptors transduce light energy into electrical signals. 3. Electrical signals transmitted to brain to allow for perception. Visual Physiology Lens refracts light rays so that they are focused on the retina. If object moves closer lens must change shape to keep focus. Visual Physiology Changing lens shape = accommodation To flatten lens, ciliary muscles relax. To make lens more round, ciliary muscles contract. Visual Physiology Hyperopia: (farsightedness) eyeball is too short, focal point behind retina. Convex lenses will correct this problem by slightly refracting the light inward before it enters the eye. Visual Physiology Myopia: (nearsightedness) eyeball is too long, focal point in front of retina. Concave lenses will correct this problem by slightly refracting the light outward before it enters the eye. Phototransduction Light travels through retinal cells, reflects off back layer of eyeball, then stimulates the photoreceptors. ­convert light energy to electrical signals at the retina. Photoreceptors Rods: ­ mostly in peripheral retina ­ function well in low light ­ monochromatic black, white, shades of gray Cones: ­ most abundant at fovea ­ color vision Signal Transmission Photoreceptors synapse on bipolar cells which project to ganglion cells. nd Optic Nerve (II 2 Cranial Nerve) Ganglion cells form optic nerve. Optic nerve and blood supply to eye go through optic disk. No photoreceptors at optic disk = blind spot Visual Pathway Ganglion cells from the nasal hemiretinas cross at the optic chiasm. Ganglion cells from the temporal hemiretinas stay on the same side. Synapse on neurons in lateral geniculate nucleus in the thalamus that project to primary visual cortex (V1). Cortical Processing V1 projects to ventral and dorsal visual streams Ventral stream: the “what pathway” Temporal lobe ­face matching task Dorsal stream: the “where pathway” Parietal lobe ­location matching task Cortical Processing Ventral and dorsal streams composed of many functionally separate visual areas. Many areas are interconnected Each area contributes more complex information as move from V1 through each stream. Cortical Damage Damage to the dorsal stream can cause deficits in perceiving Damage to the dorsal stream can cause deficits in perceiving portions of space or visual motion. A stroke affecting the right parietal cortex results in visual (spatial) neglect. Cortical Damage Damage to the ventral stream can cause deficits in perceiving object color, shape, etc. Certain areas of the ventral stream specifically process face stimuli. A stroke affecting these areas can lead to prosopagnosia ­ difficulty recognizing faces. Eye Movements Eye Movements Eye Movements Eyes are moved with 6 extraocular muscles acting as 3 agonist­ Eyes are moved with 6 extraocular muscles acting as 3 agonist­ antagonist pairs: Intorsion Elevation Abduction Adduction Depression Extorsion Right Eye Cranial Nerves Eye Movements Extraocular muscles controlled by 3 cranial nerves: Oculomotor Nerve (III) Oculomotor Nerve (III) Superior Division ­superior rectus (elevation) Inferior Division ­ medial rectus (adduction) ­ inferior rectus (depression) ­ inferior oblique (extortion) Trochlear Nerve (IV) Trochlear Nerve (IV) Superior Oblique (intortion) Abducens Nerve (VI) Abducens Nerve (VI) Lateral Rectus Abducens = “abducts” Eye Movements Lesions to extraocular muscles or nerves leads to misalignment of Lesions to extraocular muscles or nerves leads to misalignment of the eyes and diplopia. ­(double vision) Normal R. Abducens Nerve Lesion R L R L Eye Movements There are 5 types of eye There are 5 types of eye movements: 1. Saccades ­very fast jumping movements of the eyes from one position to another ­bring new images of interest onto fovea ­REM sleep (saccadic sleep) Infrared corneal reflection Eye Movements There are 5 types of eye There are 5 types of eye movements: 2. Smooth Pursuit ­track moving objects smoothly ­maintain image on fovea ­image on fovea is necessary ­eyes cannot be closed for this movement to occur, which differs from saccades Eye Movements Aligning eyes with vergence eliminates retinal disparity. There are 5 types of eye There are 5 types of eye movements: 3. Vergence 4. Vestibulo­ ocular reflex (VOR) 5. Optokinetic nystagmus Neural Control of Eye Movements Neural Control of Eye Movements Eye movements controlled in the brainstem: superior colliculus Superior colliculus affected by several cortical and subcortical sites. ...
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This note was uploaded on 02/09/2011 for the course MOVESCI 110 taught by Professor Katch during the Spring '08 term at University of Michigan.

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