Slide 1 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Bear: Neuroscience: Exploring the Brain 3e Chapter 09: The Eye

Slide 2 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Introduction Significance of vision Relationship between human eye & camera Retina Photoreceptors: Converts light energy into neural activity Detects differences in intensity of light Lateral geniculate nucleus (LGN) First synaptic relay in the primary visual pathway Visual information ascends to cortex  interpreted and remembered

Slide 3 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Properties of Light Light Light and electromagnetic radiation Electromagnetic radiation Wavelength, frequency, amplitude Hot colors: Orange, red Cool colors: blue, violet

Slide 4 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Properties of Light Optics Study of light rays and their interactions Reflection Bouncing of light rays off a surface Absorption Transfer of light energy to a particle or surface Refraction Bending of light rays from one medium to another

Slide 5 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Structure of the Eye Gross Anatomy of the Eye Pupil: Opening where light enters the eye Sclera: White of the eye Iris: Gives color to eyes Cornea: Glassy transparent external surface of the eye Optic nerve: Bundle of axons from the retina

Slide 6 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Structure of the Eye Ophthalmoscopic Appearance of the Eye

Slide 7 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Structure of the Eye Cross-Sectional Anatomy of the Eye Aqueous Humor: Fluid nourishing cornea Ciliary muscles: Ligaments that suspend lens Lens: Change shape to adjust focus Divides eyes into two compartments Aqueous humor in anterior chamber Jelly-like vitreous humor in posterior chamber

Slide 8 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Image Formation by the Eye Introduction Eye collects light, focuses on retina, forms images Refraction of light by the cornea

Slide 9 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Image Formation by the Eye Accommodation by the Lens Changing shape of lens allows for extra focusing power

Slide 10 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Image Formation by the Eye The Pupillary Light Reflex Connections between retina and brain stem neurons that control muscle around pupil Continuously adjusting to different ambient light levels Consensual Pupil similar to the aperture of a camera

Slide 11 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Image Formation by the Eye The Visual Field Amount of space viewed by the retina when the eye is fixated straight ahead Visual Acuity Ability to distinguish two nearby points Visual Angle: Distances across the retina described in degrees

Slide 12 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Microscopic Anatomy of the Retina Photoreceptors: Cells that convert light energy into neural activity Direct (vertical) pathway: Horizontal cells Amacrine cells Ganglion cells Photoreceptorsbipolar cells ganglion cells

Slide 13 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Microscopic Anatomy of the Retina The Laminar Organization of the Retina Cells organized in layers Inside-out

Slide 14 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Microscopic Anatomy of the Retina Photoreceptor Structure Electromagnetic radiation to neural signals Four main regions Outer segment Inner segment Cell body Synaptic terminal Types of photoreceptors Rods and cones

Slide 15 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Microscopic Anatomy of the Retina Regional Differences in Retinal Structure Varies from fovea to retinal periphery Peripheral retina Higher ratio of rods to cones Higher ratio of photoreceptors to ganglion cells More sensitive to light

Slide 16 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Microscopic Anatomy of the Retina Regional Differences in Retinal Structure (Cont’d) Cross-section of fovea: Pit in retina Structure: Maximizes visual acuity Central fovea: All cones (no rods) 1:1 ratio with ganglion cells Area of high visual acuity

Slide 17 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Phototransduction Phototransduction in Rods Depolarization in the dark: “Dark current” Hyperpolarization in the light One opsin in rods: Rhodopsin Receptor protein that is activated by light

Slide 18 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Phototransduction Phototransduction in Cones Similar to rod phototransduction Different opsins Red, green, blue Color detection Contributions of blue, green, and red cones to retinal signal Spectral sensitivity Young-Helmholtz trichromacy theory of color vision

Slide 19 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Phototransduction Dark and Light Adaptation Dark adaptation—factors Dilation of pupils Regeneration of unbleached rhodopsin Adjustment of functional circuitry All-cone daytime visionAll-rod nighttime vision 20–25 minutes

Slide 20 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Phototransduction Dark and Light Adaptation Calcium’s Role in Light Adaptation Calcium concentration changes in photorteceptors Indirectly regulates levels of cGMP  channels

Slide 21 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Retinal Processing Research by Keffer Hartline, Stephen Kuffler, and Horace Barlow Research study Action potential discharges retinal ganglion cells Retina: Stimulated with light

Slide 22 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Retinal Processing Transformations in the Outer Plexiform Layer Photoreceptors Release neurons when depolarized Bipolar Cell Receptive Fields

Slide 23 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Retinal Output Ganglion Cell Receptive Fields On-Center and Off-Center cells Responsive to differences in illumination

Slide 24 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Retinal Output Types of Ganglion Cells Categories based on appearance, connectivity, and electrophysiological properties Two types of ganglion cells in monkey and human retina M-type (Magno) and P-type (Parvo) Color-Opponent Ganglion Cells

Slide 25 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Retinal Output Parallel Processing Simultaneous input from two eyes Information from two streams is compared in the central visual system Depth and the distance of object Information about light and dark: ON- center and OFF-center ganglion cells Different receptive fields and response properties of retinal ganglion cells: M- and P- cells, and nonM-nonP cells

Slide 26 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Concluding Remarks Light emitted by or reflected off objects in space  imaged onto the retina Transduction Light energy converted into membrane potentials Phototransduction parallels olfactory transduction Electrical-to-chemical-electrical signal Mapping of visual space onto retinal ganglion cells not uniform

Slide 27 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins End of Presentation