Vision Quiz

Wavelength

Color

Amplitude

Brightness

Unit of light

Photon

Light

Energy or electromagnetic radiation

Visible spectrum

Lightwaves from 400 nm to 750 nm

Conjunctiva

Clear, thin membrane that covers part of the front surface of the eye and the inner surface of the eyelids

Cornea

Protective layer that covers the iris, pupil, and anterior chamber

Sclera

White part of eye that surrounds cornea

Aqueous humor

Provides nutrients and maintains shape of eye in anterior eye chamber

Pupil and iris

Help regulate the amount of light

Lens

Refracts and focuses light on the retina

Vitreous humor

Phagocytic cells and collagen fibers within the posterior eye chamber

Retina

Contains photoreceptors

Optic nerve

Axons from photo receptors

Process of vision

1. Light reflects off an object

2. Light travels to eye

3. Enters through pupil

• Cornea angles light

4. Light strikes retina

Types of photoreceptors

Rods and cones

Macula

Contains fovea

Fovea

Center of visual field with the highest acuity

Retina

Contains photoreceptors, macula, fovea, and optic disc

Optic disc

Where optic nerve attaches

Red eye

Flash is too fast for pupil to close, reflects blood in vascular tunic

Rods

Detect the amount of light, shapes, and contrast. Sensitive to low levels of light. Found in peripheral retina and are the most plentiful. Have poor acuity

Cones

Detect color and are sensitive to moderate and high levels of light. They are found in central retina. Have excellent acuity and are trichromatic

Center of retina

Fovea, few rods, more cones, great acuity

Peripheral retina

Mostly rods, low amount of cones, low acuity

Blind spot

No photoreceptors and is where the optic nerve leaves the eye

Location of photoreceptors

The very back of the eye, light must pass through layers of ganglion, bipolar, amacrine and horizontal cells

Outer segment of photoreceptors

Lamellae, photopigment molecules, where transduction oocurs

Inner segment of photoreceptors

Cell body, produce NTS, proteins, and other cellular machinery

Synaptic terminal

Releases neurotransmitters

Amacrine cells

Connect retinal ganglion cells to bipolar cells

Bipolar cells

Connection amacrine cells to horizontal cells

Horizontal cells

Connect horizontal cells to photoreceptors

Structure of retina

Retinal ganglion cells, amacrine cells, bipolar cells, horizontal cells, and photoreceptors

Rhodopsin

Photopigment in rods, Opsin or retinal

Opsin

Protein in rhodopsin

Retinal

Lipid in rhodopsin

Photoisomerization

When light strikes retinal and causes conformational change leading to release of NT

Special qualities of photoreceptors and bipolar cells

Do not generate a true action potential, generate graded potential

Special quality of ganglion cells

Respond to units of change, produce an action potential

Neural convergence

120 rods and 6 cones per ganglion cell, 1:1 ratio in fovea

Lateral inhibition

The capacity of an excited neuron to reduce the activity of neighboring neurons

Effects of lateral inhibition

Disables spreading of APs, enhances sensory perception, increase contrast/sharpness, edge responses

On-Center/Off-Surround

Light hits edge=inhibition

Light hits middle=excitation

Off-Center/On-Surround

Light hits edge=excitation

Light hits middle=inhibition

From the retina to the brain

Retina→Optic Nerve→ Optic Chiasm→ Optic tract (superior colliculus)→ LGN→ Optic radiations→ Primary visual cortex

Lateral Geniculate Nucelus

Composed of Magnocellular layers, Parvocellular layers, and Koniocellular layers

Magnocellular layer

Inner layers (1 & 2) that receive information from rods. Process form, movement, depth and brightness, and have large receptive fields

Parvocellular Layers

Outer layers (3-6) and receive information from cones. Deal with color, detail, and have small receptive fields

Koniocellular layers

Between each layer and receive information from short wave cones (blue)

Organization of striate cortex

Organized in layers

Dorsal pathway

Magnocellular (where), deals with guidance of actions and spatial awareness

Ventral pathway

What pathway that deals with object recognition, form representation, and color

Information of dorsal pathway

Travels up the cerebral cortex

Information of ventral pathway

Travels alongside the ventral side of the brain

Dorsal stream

Contains detailed map of visual field, detects and analyzes movements

Conditions associated with dorsal stream

Optic ataxia and Akinetopsia

Optic ataxia

Unable to use visuospatial information to guide arm movements

Akinetopsia

Motion blindness

Ventral stream

Strong connection with limbic system, influenced by extraretinal factors, crucial in judging object significant

Conditions associated with ventral stream

Visual agnosia and prosopagnosia

Visual agnosia

Inability to recognize objects

Prosopagnosia

Face blindness