Lecture 23: The Eye & Lecture 24: Retinal Circuitry

1. Cornea (matching)

clear outer covering

2. Iris

controls the size of the pupil

3. Pupil

focuses light on the retina

4. Lens

hole that lets the appropriate amount of light in

5. Ciliary muscle

pulls on the lens to focus at different distances

6. Sclera

outermmost layer, white

7. Retina

sensory organ of the visual system

8. Fovea

part of the retina with greatest acuity

Optic Disk

where blood vessels and nerves leave the eye

Describe the shape of the lens when we focus on far away images vs. the lens shape when

we focus on close objects

focus away = lens are thin and flat (unaccommodated)

Focus near = lens are thick and found (accommodated)

True or false: Myopia occurs because the lens cannot accommodate enough to focus near
objects correctly

false: Myopia occurs because the lens cannot accommodate enough to focus near
objects correctly
Explanation: Myopia (nearsightedness) occurs when because lens cannot
accommodate enough to focus far objects correctly (always focuses in front of
retina)
The above statement is true regarding hyperopia (farsightedness)

Where is the blind spot in the eye?

the blind spot of the eye is in the optic disk

Why is the blind spot in the eye called the blind spot?

All
outputs of the retina meet there and no photoreceptors are present

What happens to a photoreceptor when light is detected

it hyperpolarizes

is more neurotransmitter released in in the dark or the light from a photoreceptor?

the dark

what kind of channels close when light is detected

cGMP-gated Na+ and Ca2+ channels

rods have ___ light sensitivity and ___ spatial resolution

high, low

cones have ___ light sensitivity and ___ spatial resolution

low, high

bipolar cells connect ____ to ____?

bipolar cells connect photoreceptors to ganglion cells

Parvocellular (P) cells are associated with rods or cones?

cones

Magnocellular (M) cells are associated with rods or cones?

rods

Describe the difference between an on-center ganglion cell and an off-center ganglion cell:

On-center ganglion cells have a burst of action potentials when there is light in the

center of the receptive field

Off-center ganglion cells have a decrease in action potentials when there is light in

the center of the receptive field

what kind of NT do ALL photoreceptors use?

GLUTAMATE

• When light shines onto a center cone cell, will the on-center bipolar cell depolarize or
  hyperpolarize?

DEPOLARIZES

What kind of receptor is acted upon when a cone contributes to the on portion of a
receptive field?

Metabotropic glutamate receptors (inhibitory effect = sign changing

which means more firing in the photoreceptor = less firing in the ganglion cell

When light shines onto a center cone cell, will the off-center bipolar cell depolarize or
hyperpolarize?

Ionotropic glutamate receptors (these are sign conserving which

means that more firing in the photoreceptor = more firing in the ganglion cell)

When light shines onto a center cone cell, will the on-center ganglion cell depolarize or
hyperpolarize?

depolarize

When light shines onto a center cone cell, will the off-center ganglion cell depolarize or
hyperpolarize

hyperpolarize

Surround/center cone cells will excite/inhibit a horizontal cell which in return will make
the horizontal cell excite/inhibit the cone cell.

Surround/center cone cells will excite a horizontal cell which in return will make the

horizontal cell inhibit the cone cell

what is lateral inhibition:

When an excited neuron (in this case the horizontal cell)

inhibits the actions of its neighboring neurons (surround/center cells)