Transcript Chapter 09 - The Eye

Bear: Neuroscience: Exploring the
Brain 3e
Chapter 09: The Eye
Slide 1
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 2
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 3
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 4
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 5
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 6
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 7
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 8
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 9
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 10
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 11
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:
Photoreceptors
bipolar cells
ganglion cells
Horizontal cells
Amacrine cells
Ganglion cells
Slide 12
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 13
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 14
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 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
(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 16
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 17
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
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
Slide 18
Phototransduction
Dark and Light Adaptation
All-cone daytime vision
All-rod nighttime vision
20–25 minutes
Dark adaptation—factors
Dilation of pupils
Regeneration of unbleached rhodopsin
Adjustment of functional circuitry
Slide 19
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 20
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 21
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 22
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 23
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 24
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: ONcenter and OFF-center ganglion cells
Different receptive fields and response
properties of retinal ganglion cells: M- and
P- cells, and nonM-nonP cells
Slide 25
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 26
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins
End of Presentation
Slide 27
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins