22/11/19 eye

Question 1

What is light?

Answer 1

Packets of energy called photons.

Photons travel in waves and have a specific wavelength

Question 2

What interprets different wave length?

Answer 2

Rods and cones

Question 3

What is the visible light spectrum

Answer 3

400-700 nm

Question 4

What happens when speed of light changes?

Answer 4

It refracts.

Question 5

What is the focal point?

Answer 5

Point at which light rays and a ll light of the same source converge. Must be on retina.

Question 6

What is focal distance

Answer 6

Distance between the centrepoint of the lens and the focal point

Question 7

What is a real image

Answer 7

Image formed by a convex lens.

Question 8

Relationship between a convex lens and focal distance?

Answer 8

The more convex the lens, the shorter the focal distance.

Question 9

Difference between a concave and convex lens?

Answer 9

A convex lens focuses light rays to a specific focal point vs a concave lens that diverges or seperates light rays.

Question 10

Process when a convex lens refracts light?

Answer 10

• Rays converge on a single point.
• image is inverted
• image is interpreted by brain

Question 11

What parts of the eye refract light?

Answer 11

The cornea does majority of work, but as it can’t change shape is always constant. The lens does the rest of the work

Question 12

Role of the lens in refraction

Answer 12

The lens must change shae for second part of refraction (following cornea) so the focal point will land on retina.

Question 13

When does light get refracted?

Answer 13

3 times, when it enters the cornea, when it enters the lens, and when it leaves the lens.

Question 14

Role of the cornea?

Answer 14

First part of eye that refracts light, determines distance.

Question 15

Light refraction when object is far away + small?

Answer 15

Rays come in parallel.
Not much refraction is necessary to converge focal point on retina, so cornea does most of work.
- Ciliary muscles of cilliary body are relaxed and ciliary zonules are tight = thin, flat lens. Uses sympathetic nervous system.

Question 16

Light refraction when object is close + large? Lens accommodation?

Answer 16

• Rays not parallel.
• Need lots of refraction, so lens must contribute more by bulging (ciliary muscles of ciliary body contract, ciliary zonules loosen and lens bulges = pushing focal point towards retina.
• Sphincter pupillae of iris also play a role in constricting pupil.

Question 17

What is far view vision?

Answer 17

20 or more feet away.

Question 18

What is close vision?

Answer 18

less than 20 feet away.

Question 19

What is near point of vision?

Answer 19

The closest point you can see an image clearly.

Question 20

Explain Emmetropia (classifying vision).

Answer 20

Normal vision

Question 21

Explain Myopia (classifying vision)

Answer 21

Near sighted, eye ball too long, see close not far away.

Focal point falls before retina.

Need concave contacts.

Question 22

Explain Hyperopia (classifying vision)

Answer 22

Farsighted, eye is too short, see far away but struggle with close.

Focal point falls behind retina.

Need convex contacts/glasses to shorten focal distance.

Question 23

Explain Astigmatism (classifying vision)

Answer 23

Unequal curvatures of cornea or lens.

Need specific contacts for you.

Question 24

What is macula degeneration?

Answer 24

Degeneration of the macula lutae (where the fovea centralis is located).

Question 25

Function of photoreceptors?

Answer 25

Outer segment:
plasma membrane infolding (like discs) with light absorbing pigment.

Inner segment contains organelles.

The end of a photoreceptor has an axon terminal that forms a synapse between the photorecptor and the bipolar cells.

Question 26

What the plasma membrane in photoreceptors do?

Answer 26

Increses surface area, increasing visual pigment.

Question 27

What pigment and associated protein are present in plasma membrane infoldings of phtoreceptors?

Answer 27

• Visual pigment called retinal

- associated protein called opsin which determines wave length of light that retinal can absorb.

Question 28

Pigment and rods and cones:

Answer 28

Rods absorb one type of visual pigment.

Cones absorb 3 types, green, red, and blue.

Each uses a different type of opsin.

Question 29

When is a graded potential formed? (phototransduction)

Answer 29

Once pigment abosrbs light - retinal changes shape (bent to straight) - retinal and opsin seperate = triggers transduction (graded potential)

Question 30

Retinal and opsin in the dark and light

Answer 30

In the dark:
Retinal and opsin are bound together.

In the light:
Retinal absorbs light and seperates from opsin.

Question 31

Phototransduction in the dark:

Answer 31

Photoreceptors depolarize and are ON
Bipolar OFF
Ganglion OFF

small continuous depolarization occuring.
This opens ligand gated ion channels and allows positive ions to flow into cell. Takes membrane past threshold and creates an AP.

Photoreceptors release NT at synapse with bipolar cells, NT is inhibitory (IPSP) = bipolar cells don’t send an AP = ganglion cells can’t fire.

Question 32

Phototransduction in the light:

Answer 32

Photoreceptors hyperpolarization as cyclic GAM cation channels close and are OFF
Bipolar ON
Ganglion ON = info sent

Hyperpolarization occurs in photoreceptor cells. As there is no IPSP, bipolar cells depolarize and send AP.
When it reaches ganglion, EPSP released and info sent to brain via optic nerve.

Question 33

Role of G-protein coupled receptors in phototransduction

Answer 33

In light when retinal seperates from opsin - activates associated g proteins (this is transduction) - these then go and activate the enzyme PDE - this converts clyclic GMP to GMP (removing ligand required for channel to open and depol can’t occur).

Question 34

Optic nerve?

Answer 34

collection of ganglion axons - has branch for each eye (some optic nerve fibers cross depending on where light hits).