Special Senses Vision

Question 1

Describe light rays and the eye for objects nearby

Answer 1

Light rays are still diverging

It takes more refraction (bending) to make diverging rays focus on the retina

Question 2

Describe the cornea and refraction

Answer 2

The cornea is the first site in the eye where refraction occurs
It bends the light the most of any structure in the eye and accounts for 2/3 of the ability of the eye to bend light
Amount of bending is fixed

Question 3

What does accommodation require?

Answer 3

Ciliary muscle
Suspensory ligaments
Lens

Question 4

What does near vision require?

Answer 4

Requires contraction of the ciliary muscle
As the ciliary muscle contracts, the tension on the suspensory ligaments is released
The suspensory ligaments become slack
The natural elasticity of the lens causes the lens to become rounder
The increased curvature of the lens increases the refractive power of the lens

Question 5

Describe contraction of the ciliary muscle and diopters during life

Answer 5

In young kids, this adds 20 diopters
In young adults, loss of elasticity results in strength of 10 diopters
By the 50’s, loss of elasticity results in 1 diopter

Question 6

What does increased curvature of the lens do to light rays?

Answer 6

Allows the light rays from a nearby object to be bent sufficiently to bring them into focus on the retina

Question 7

What does far vision require?

Answer 7

Requires relaxation of the ciliary muscle
As the ciliary muscle relaxes, the tension on the suspensory ligaments is increased
Suspensory ligaments become taut, which pulls the lens into a flat position
The decreased curvature of the lens decreases the refractive power of the lens

Question 8

Besides contraction of the ciliary muscles, what else does near vision require?

Answer 8

Convergence of the eyes to point of focus

Constriction of the pupil

Question 9

How does constriction of the pupil help near vision?

Answer 9

By constricting the pupil, the opening for light to enter is reduced
This eliminates some of the diverging light rays and allows better focus

Question 10

What is the vertical pathway of the retina composed of?

Answer 10

Photoreceptor
Bipolar cell
Ganglion cell

Question 11

Describe photoreceptors and release of glutamate

Answer 11

When it is dark (no stimulation), the release of glutamate is high
When a photon activates the photoreceptor, the release of glutamate decreases
Light hyperpolarizes rods and cones

Question 12

Describe vertical pathway for cones

Answer 12

Photoreceptor is struck by a photon of light

This decreases glutamate release onto a bipolar cell

Question 13

Describe on-center bipolar cells

Answer 13

Activation of a photoreceptor in the center of the bipolar cell’s receptive field causes depolarization of the bipolar cell
Activation of a photoreceptor in the surrounding region causes hyperpolarization of the bipolar cell

Question 14

Describe off-center bipolar cells

Answer 14

Activation of a photoreceptor in the center of the bipolar’s receptive field causes hyperpolarization of the bipolar cell
Activation of a photoreceptor in the surrounding region causes depolarization of the bipolar cell

Question 15

What happens if a photoreceptor activates an on-center bipolar cell?

Answer 15

A metabotropic receptor is activated
Neurotransmitter release causes a decrease in cation influx
In the dark, the on-center cell is hyperpolarized
With light, release of glutamate from the photoreceptor decreases, so the cation current increases, and the on-center cell is depolarized

Question 16

What happens when the photoreceptor activates an off-center bipolar cell?

Answer 16

An AMPA receptor is activated
Neurotransmitter release causes an increase in cation influx
In the dark, the off-center cell is depolarized
With light, glutamate release from the photoreceptor decreases, the AMPA receptor is not activated, and the off-center cell is hyperpolarized

Question 17

Describe on-center and off-center ganglion cells

Answer 17

Cells are what the connecting bipolar cells is
The bipolar cell releases glutamate to excite the ganglion cell
Ganglion cell axons become fibers on the optic nerve
Cause action potentials
Relies on glutamate as neurotransmitter

Question 18

Describe the vertical pathway for rods

Answer 18

Composed of many rods
Converge on one on-center bipolar cell
Which then synapses on an A11 amacrine cell
Which synapses on a cone on-center bipolar cell
Which then activates on a ganglion cell

Rods do well in low-light situations

Question 19

What is the role of on- and off-center cells?

Answer 19

On-center cell tells us where something is

Off-center cell tells us where it ends

Question 20

What do amacrine and horizontal cells do?

Answer 20

Provide inhibitory signals that modify the activity of neighboring photoreceptors, bipolar cells, or ganglion cells

Question 21

The retina from each eye sees ____ visual fields

Answer 21

Two different

Question 22

Describe activation of temporal retina and nasal retina

Answer 22

The left temporal retina is activated by light coming from the right visual field as is the right nasal retina
The right temporal retina is activated by light coming from the left visual field as is the left nasal retina

Question 23

Describe the axons in the optic chiasm

Answer 23

The axons from the nasal retina on each side will cross and join the axons from the temporal retina
All the information from the right visual field is sent to the same part of the brain (in the case of the right visual field, the left side of the brain)

Question 24

What are the functions of the lateral geniculate body?

Answer 24

Control the motions of the eyes, so they converge on the desired point of interest (convergence/divergence)
Control focusing so that the image we are interested in is in best focus possible
Identify major elements within our visual image and send that identification to the cortex
Identify motion within our visual image

Question 25

Describe the 6 layers of the primary visual cortex

Answer 25

Layers 1, 2, and 3 allow networking between primary visual cortex and other parts of the cortex
Layer 4 receives inputs from the lateral geniculate nucleus
Layers 5 and 6 send information back to LGN

Question 26

Describe the columns in the cortex

Answer 26

Cortex is composed of columns that start from surface of cortex and extend through all 6 layers
Each column does a different job
Neighboring columns have related jobs
If one column detects horizontal edges, neighboring column detects edges oriented at 30 degrees

Question 27

What is the major job of the primary visual cortex V1?

Answer 27

Identify the edges/contours of components in our visual image

Question 28

What is the major job of V2?

Answer 28

Identify disparities in the visual images presented by the two eyes
Disparities between the two eyes are used for depth perception

Question 29

What are blobs?

Answer 29

Collections of neurons within the columns

Enable color detection

Question 30

What is the major role of V4?

Answer 30

Complete processing of color inputs

Question 31

What does the dorsal pathway that leaves the occipital cortex do?

Answer 31

Relays visual information to the motor cortices and enables us to complete motor acts based on visual input

Question 32

What does the ventral pathway do?

Answer 32

Relays visual information to areas of the brain involved in higher processing of sensory inputs
Integration of visual input with other sensory inputs allows us to use that visual image to accomplish higher order functions, including naming the object and copying the object

Question 33

Describe the light rays and the eye for objects far away

Answer 33

Light rays have diverged far enough that only parallel light rays enter the eye
Therefore, it doesn’t take much refraction to make parallel rays focus on retina