626 Visual System - 1 V isual S ystem I : P eripheral 1....

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Unformatted text preview: 1 V isual S ystem I : P eripheral 1. The Eyeball: Like a camera 2. The Retina: Five cells types 3. Receptors: Phototransduction 4. Retinal Processing: High fidelity 5. Retinal Projections to the Brain Human Neuroanatomy The Eyeball Anatomy of Eye: Optics of the lens focuses & inverts the image on the retina at the back of the eye. The intrinsic muscles (smooth) control the Pupil & Lens , and are innervated by ANS: (accommodation & luminance) The six extrinsic muscles (somatic) of each eye control conjugate sacccades , and are innervated by cranial nerves 3, 4, & 6. (perception) Vision is an active event 2 The Eyeball The Fundus Choked Disk: ICP The Retina Five Types of Retinal Cells: Receptor > H > Bipolar > A > Ganglion Cells 2 The Eyeball The Fundus Choked Disk: ICP The Retina Five Types of Retinal Cells: Receptor > H > Bipolar > A > Ganglion Cells 3 Receptors Rod and Cone outer segments contain: Photopigment : Rhodopsin = ( Opsin + Retinal ) Phototransduction What is SensoryTransduction? Where physical energy is changed to neural energy ( Vm ) Phototransduction: Photoreceptors Hyper polarize to light! (Receptors are depolarized in the dark due to dark current [Na+ current], with steady release of glutamate . Photon > cis-trans isomerization of rhodopsin > Activates transducin > Activates phosphodiesterase > Destroys cGMP on Na+ channel > NA+ channel closes > Reduces membrane gNa + > Receptor hyperpolarizes > (less glutamate released) . 4 Retinal Processing In the Straight Through Path: Receptors ( Hyper polarize) > Bipolars ( De polarize) > RGC ( Action Potential ) However-- with the addition of the Horizontal & Amacrine Cells : Contrast is Enhanced through a process called Lateral Inhibition Retinal Processing Lateral Inhibition Enhances contrast of RGC receptive fields Example: Illusion of Mach Bands Horizontal cells suppress excitability of adjacent bipolars & RGCs 5...
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626 Visual System - 1 V isual S ystem I : P eripheral 1....

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