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NROC64H3 Study Guide - Outer Plexiform Layer, Pupillary Light Reflex, Inner Plexiform Layer

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Matthias Niemeier

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Chapter 9
The eye
Vision: Based on the light bounced into our eyes from objects, we make sense of a complex world.
Light: Electromagnetic energy that is emitted in the form of waves. The waves are:
1. Absorbed
2. Scattered
3. Reflected
4. Bent
Retina: Located at the back of the eye. Contains photoreceptors specialized to convert light energy into
neural activity.
Eye: Automatically adjusts to differences in illumination and automatically focuses itself on objects of
interest. The eye can track moving objects and keep its surface clean (via blinking and tears). Each eye
has two overlapping retinas:
1. One specialized for low light levels that we encounter from dusk to dawn
2. One specialized for higher light levels and for the detection of color from sunrise to sunset.
Function of the retina: Specialized to detect differences in the intensity of light falling on different parts
of it. Image processing begins in the retina before any visual information reaches the rest of the brain.
Optic nerve: Axon bundles of retinal neurons which distribute visual information (in the form of action
potentials) to several brain structures that perform different functions.
Targets of the optic nerves:
1. Involved in regulating biological rhythms
a. Synchronized with the light-dark daily cycle.
2. Involved in the control of eye position and optics.
Lateral geniculate nucleus: The LGN serves as the first synaptic relay in the pathway that serves visual
perception. It is located in the dorsal thalamus. From the LGN, visual information ascends to the cerebral
cortex, where it is interpreted and remembered.
Chapter summary:
1. Explore eye and the retina
2. See how light carries information to our visual system
3. How the eye forms images on the retina

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4. How the retina coverts light energy into neural signals that can be used to extract information
about luminance and color differences
Properties of light
Visible light: Light is the electromagnetic radiation that is visible to our eyes. Consists of wavelengths
400-700 nm.
Electromagnetic radiation: Described as a wave of energy. Characterized by:
1. Wavelength
a. The distance between successive peaks or troughs
2. Frequency
a. The number of waves per second
b. The energy content of electromagnetic radiation is proportional to its frequency
i. Radiation emitted at high frequency (short wavelengths) has highest energy
ii. Radiation emitted at lower frequencies (longer wavelengths) have less energy
3. Amplitude
a. The difference between wave trough and peak.
Optics: The study of light rays and their interactions. Interactions include:
1. Reflection
2. Absorption
3. Refraction
Reflection: The bouncing of light rays off a surface. Most of what we see is light that is reflected off
objects in our environment
Absorption: Transfer of light energy to a particle or surface. Light sensitive photoreceptor cells in the
retina contain pigments and use the energy absorbed from light to generate changes in membrane
Refraction: The bending of light rays that can occur when they travel from one transparent medium to
another. This bending occurs because of the speed of light between two mediums. Images are formed in
the eye by refraction.
The structure of the eye
The eye: Specialized organ for the detection, localization and analysis of light.
Gross anatomy of the eye

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Pupil: The opening that allows light to enter the eye and reach the retina; it appears dark because of the
light absorbing pigments in the retina.
Iris: Surrounds the pupil. The pigmentation of the iris is what we call the eye color. The iris contains two
muscles that can vary the size of the pupil:
1. One makes it smaller when it contracts
2. One makes it larger when it relaxes.
Cornea: The glassy transparent external surface of the eye that covers the pupil and iris.
Sclera: The white of the eye which forms the tough wall of the eyeball. It is continuous with the cornea.
Inserted into the sclera are three pairs of extraocular muscles which move the eyeball in the orbit.
These muscles are normally not visible because they lie behind the conjunctiva.
Conjunctiva: A membrane that folds back from the inside of the eyelids and attaches to the sclera
Eye’s orbit: The bony eye socket in the skull.
Optic nerve:
1. Carries axons from the retina
2. Exits the back of the eye
3. Passes through the orbit
4. Reaches the base of the brain near the pituitary gland
Ophthalmoscopic appearance of the eye
Ophthalmoscope: Device that enables one to peer into the eye through the pupil to the retina.
Retina through ophthalmoscope: Obvious feature is the blood vessels on its surface. These retinal
vessels originate from a pale circular region called the optic disk. The optic disk is also where the optic
nerve fibers exit the retina.
Sensation of light: Cannot occur at the optic disk because there are no photoreceptors. Also cannot
occur where large blood vessels exist because the vessels cast shadows on the retina. We are not aware
of any holes in our field of vision because the brain fills in our perception of these areas.
Macula: Located at the middle of each retina. It is a darker colored region with a yellowish hue. I is the
part of the retina for central (as opposed to peripheral) vision. The macula is distinguished by the
relative absence of large blood vessels. This absence of blood vessels improve the quality of central
Fovea: A dark spot about 2mm in diameter. It lies in the center of each retina and is surrounded by the
macula. It is classified as:
1. Temporal
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