Section 3: The Eye

Bouncing of light rays off a surface can be described as _________.

reflection

Transfer of light energy to a particle or surface → color is described as __________.

absorption

Bending of light rays (cornea, lens) is known as ________________.

refraction

The mucous membrane that covers the front of the eye and lines the inside of the eyelids is called the _____________.

conjunctiva

What are the three layers of the eyeball?

fibrous layer → vascular layer (uvea) → inner layer (retina)

What structures of the eye make up the fibrous layer of the eyeball?

sclera and cornea

The ______________ is the white layer of dense connective tissue (White of the eye).

sclera

The ____________ covers the entire eyeball except for the _________.

sclera, cornea

The vascular layer (uvea) is composed of what structures?

choroid, ciliary body, iris (pupil)

The ____________ lines most of the internal surface of the sclera.

choroid

The choroid is highly ___________________ and contains ______________.

highly vascularized and contains melanocytes

____________ pigments absorb stray light rays and prevent reflection and scattering of light in the eyeball.

Melanin

____________ ______________ contain blood capillaries and secretes aqueous humor.

Ciliary processes

__________ ___________ extend from ciliary processes and attach to the lens.

Zonular fibers (Suspensory ligaments)

____________ muscle is circular smooth muscle that adapts the lens for near and far vision.

Ciliary muscle

Adapts the lens for near and far vision = _____________.

accommodation

The ________ is the colored portion of the eyeball - between the cornea and the lens; attached to the ciliary process.

iris

The _______ is the hole in the center of the iris.

pupil

The ___________ regulates the amount of light entering the eye.

iris

Dilator pupillae (Radial) muscles ___________ the pupil in size. 

increase the pupil in size (dilation)

Sphincter pupillae (Circular) muscles _____________ in the size of the pupil.

decrease in the size of the pupil (constriction).

What structures make up the retina?

Macula/Fovea centralis, optic disc, ora serrata

The ______________ ________ is the yellow spot at the posterior center of the retina and has a relative absence of large blood vessels.

macula lutea

The _________ __________ is the highest visual acuity (resolution) and contains only cones. 

fovea centralis 

The _________ _________ is the exit site of the optic (II) nerve and blood vessels enters the eyeball.

optic disc

The _____________ humor fills the space between the retina and lens.

vitreous humor

The distance from the refractive surface to the point where parallel light rays converge is defined as __________ ____________.

focal distance

Reciprocal of focal distance; measurement of refractive power is defines as ____________.

diopter

The refractive power of the ______ is greater than the _________.

cornea, lens

_____________ means the refractive power of the lens can be changed (added).

Accommodation 

Accommodation by lens results in a ______ lens for far points, and a ____________ lens for near points.

results in a flat lens for far points, and a fat lens for near points

____________ is the medical terminology for normal vision.

Emmetropia

________________ is the medical terminology for farsightedness.

Hyperopia 

____________ is the medical terminology for shortsightedness.

Myopia

________ defines the total amount of space that can be viewed by the retina when the eye is fixated straight ahead.

Visual field

What is the term used to define the ability to distinguish two nearby points?

Visual acuity

________ ____________ is the distance across the retina described in degrees.

Visual angle

Trace the retinal information processing pathway.

Photoreceptors → Bipolar cells → Ganglion cells → Brain

__________ cells receive input from photoreceptors and project to other photoreceptor and bipolar cells.

Horizontal cells

_________________ cells receive input from bipolar cells and project to ganglion cells, bipolar cells, and other amacrine cells.

amacrine cells

What are the two main types of photoreceptors in the eye?

rods and cones

Three are about 92 million __________ per human retina and about 5 million __ per human retina. 

92 million rods, and 5 million cones

____________ are 1000 times more sensitive than _______.

rods are 1,000 times more sensitive than cones

________ provide vision in scotopic conditions (dim light)

Rods

What photoreceptors produce black and white vision?

Rods

__________ photoreceptors are stimulated in phototopic conditions (brighter light).

Cones

How many types of ones are there in human eyes?

3 types of cones

What are the 3 types of cones found in the human eye?

blue cones, green cones, and red cones

What are the main structural components of photoreceptors?

outer segment, inner segment, and synaptic terminal

The ____________ part of photoreceptors contains discs containing ______________.

outer segment contains discs containing photopigments 

The __________ __________ contains ONLY cones!

fovea centralis

Rods are found mostly in the ____________ _________.

peripheral retina

In the _____________ retina, relatively few photoreceptors send information to a ganglion cell => High resolution

central retina

In the ____________ retina, many photoreceptor cells provide input to a ganglion cell => detection of dim light.

peripheral retina 

_______ vision has greater visual acuity at photopic light levels (daylight).

central

________ vision is more sensitive to scotopic light levels.

peripheral

We cannot perceive color differences at ______ light levels.

scotopic

___________ is a photopigment in rods. 

Rhodopsin 

There are 4 types of photopigments: ____ in cones and ___ in rods.

3 types in cones and 1 in rods

__________ are seven transmembrane G-protein coupled receptors in photopigments.

Opsin

How many types of opsin are there in photopigments?

4 different types (3 in cones, 1 in rods)

Both opsin and __________ make up photopigments.

retinal

Retinal is a ________ derivative.

Vitamin A

______________ is the conversion of light energy received by photoreceptors into changes in membrane potential (electrical signals).

Phototransduction

Phototransduction occurs in the ______ segment of rods and cones.

outer

When the photoreceptor is at rest (in the dark), the cell is __________. 

depolarized

Activation of a photoreceptor by light causes a _______________ in receptor potential.

hyperpolarization

In the dark, the membrane potential of the rod outer segment is _____________.

depolarized

Draw out the phototransduction that occurs in the dark:

1. The enzyme guanylyl cyclase produces cyclic guanosine monophosphate (cGMP).

2. cGMP opens cGMP-gated Na+ channels, and a Na+ inflow (dark current) causes depolarization.

3. Depolarization keeps the voltage-gated Ca2+ channels open, and the Ca2+ influx triggers the release of glutamate.

Light causes a conformational change of retinal from _____-retinal to _______-retinal.

cis-retinal to trans-retinal

Draw out phototransduction that occurs in light:

1. Light causes a conformational change of retinal from cis-retinal to trans-retinal. 

2. Trans-retinal separates from opsin (bleaching). 

3. Transducin is activated.

4. Transducin activates cGMP phosphodiesterase that degrades cGMP = cGMP levels decrease.

5. cGMP Na+ channels close which causes a Na+ inflow (dark current decreases) = Hyperpolarization! 

6. Hyperpolarization decreases the number of open voltage-gated Ca2+ channels = Decrease in Ca2+ influx 

In phototransduction of light glutamate release is turned _______.

OFF

When glutamate release is turned off, ______ bipolar cells are activated and stimulate ganglion cells.

ON bipolar cells

Dark adaptation is the transition from daytime (_________) vision to night time (_______) vision.

from daytime (all-cone) vision to night time (all-rod) vision

In dark adaptation, the pupils ________, allowing _____ light to enter the eye.

the pupils dilate, allowing more light to enter the light.

In light adaptation, the pupils _____________, allowing ______ light to enter the eye.

the pupils constrict, allowing less light to enter the eye.

Only ______ cells fire action potentials.

ganglion cells

The ________ ________ is an area of the retina where light would change the firing rate of a neuron.

receptive field

Bipolar cells receive _______ and _______ inputs from photoreceptor cells.

direct and indirect inputs

What is the direct pathway for bipolar cell receptive fields?

light → photoreceptor cells → bipolar cells

What is the indirect pathway for bipolar cell receptive fields?

Light → photoreceptor cells → Horizontal cells → bipolar cells

The receptive field ______ provides a _______ input from photoreceptors to bipolar cells.

The receptive field center provides a direct input.

The receptive field ______ provides a _______ input from photoreceptors to bipolar cells via horizontal cells. 

The receptive field surround provides an indirect input.

Antagonistic center-surround receptive fields are defines as: receptive field center and receptive field surround cause _________ changes in membrane potential of bipolar cells.

opposite

Cones turn on _____ bipolar cells.

Cones turn on ON bipolar cells.

Cones turn off _____ bipolar cells.

Cones turn off OFF bipolar cells.