Lecture 6

Question 1

Light: The stimulus for Vision

Answer 1

The stimulus for vision is visible electromagnetic radiation, which can be be characterized by its wavelength.

The human visual system is sensitive to wavelengths from 400-700 nanometers (10-9 meter)

Question 2

Cornea

Answer 2

The transparent “window” into the eyeball.

No blood supply, but has nerves to feel scratches and dryness.

Highly organized structure to let light through

Quick regeneration.

MOST OF THE REFRACTION HAPPENS HERE!!

Contact lenses sit on a layer of tears in front of cornea.

Question 3

Aqueous humor

Answer 3

The watery fluid in the anterior chamber

nutrient oxygen delivery

Question 4

IRIS

Answer 4

muscular structure.

Color of your eyes.

Question 5

Crystalline lens

Answer 5

The lens inside the eye, which enables changing focus.

Focus is controlled by ciliary muscle.

Question 6

Crystalline lens

Answer 6

The lens inside the eye, which enables changing focus.

Focus is controlled by ciliary muscle.

Question 7

Zonules of Zinn

Answer 7

connect the ciliary muscles with the lens.

Question 8

Vitreous humor

Answer 8

The transparent fluid that fills the vitreous chamber in the posterior part of the eye.

80% of volume of eye.

FLOATERS: bio-debris. No concern.

Egg-whites!!

50% decrease in light from cornea to retina (where we actually “detect” light).

Question 9

Retina

Answer 9

A light-sensitive membrane in the back of the eye that contains rods & cones, which receive an image from the lens and send it to the brain through the optic nerve.

Question 10

LIGHT IS ONLY A SENSATION IF IT IS ABSORBED BY PHOTORECEPTORS IN THE RETINA.

Not all the light reaching the retina is absorbed either.
That’s why some animals have what is called:

Answer 10

TAPETUM: the colorful, shiny material located behind the retina that reflects light back through the retina to get a second chance at capturing missed photons!

Question 11

Refraction is necessary to focus light rays and this is done by…..

Answer 11

the cornea and the lens

Question 12

Accommodation

Answer 12

The lens can change its shape, and thus alter the refractive power

Question 13

Cataracts

Answer 13

loss of transparency in lens (solved with silicone implants)

Question 14

Presbyopia

Answer 14

“old sight”.

Inability to accommodate nearby objects.

Question 15

Receptors face away from light.

Question 16

Pigment Epithelium

Answer 16

nourishes receptors, non-reflective in humans & absorbs stray light

Question 17

Tapetum

Answer 17

A layer of tissue in the eye of many vertebrate animals.

It lies immediately behind the retina.

It reflects visible light back through the retina, increasing the light available to the photoreceptors.

This improves vision in low-light conditions, but can cause the perceived image to be blurry from the interference of the reflected light

Question 18

a slice of the retina, about half the thickness of a credit card.

Answer 18

photoreceptors in LAST LAYER, mostly because of the pigment epithelium (provide vital nutrients to the photoreceptors).

Question 19

100 million photoreceptors

Answer 19

Chemical signals.

Question 20

Photoreceptors

Answer 20

Cells in the retina that initially transduce light energy into neural energy.

Question 21

Rods

Answer 21

Photoreceptors that are specialized for night vision

Question 22

Cones

Answer 22

Photoreceptors that are specialized for daylight vision, fine visual acuity and color.

Question 23

Outer segment is where feeding from the epithelium occurs.

Answer 23

VISUAL PIGMENTS are made in the INNER SEGMENT and stored in OUTER segment

Question 24

CHROMOPHORE

Answer 24

the light-catching part of the visual pigments of the retina.
4 different types of pigments.

RHODOPSIN in rods.
Cones have 3 different kinds which respond to Long, medium, and short wavelengths.
.

Question 25

biochemical cascade of events:

Answer 25

1. Closing of channels to the outer segment.
2. This causes HYPERPOLARIZATION in the cell body.
3. Reduction of neurotransmitter (GLUTAMATE) at the synaptic level.

Bipolar cell knows a photon has been caught.

GRADED POTENTIALS: the more photons, the less neurotransmitter.

Only takes milliseconds

Question 26

GRADED POTENTIALS (not ACTION POTENTIALS):

Answer 26

the more photons, the less neurotransmitter.

Question 27

Fovea

Answer 27

inside macula, near optic nerve.

Question 28

Photoreceptor Density across the Retina

Answer 28

90 million rods
4 million cones.

1 degree of visual angle where no RODS, only cones. Right behind center of pupil.

BLIND IN THE DARK. Don’t look straight at faint stars.