The Visual System - the Eye and Retina

Question 1

what are some basic importance of vision?

Answer 1

to detect prey,
detect predators,
detect mates,
communicate.

Question 2

define wavelength:

Answer 2

distance between peaks or troughs in waves.

Question 3

define frequency:

Answer 3

number of waves per second.

Question 4

define amplitude:

Answer 4

difference between wave peak and trough.

Question 5

light rays interact in 3 ways:

Answer 5

reflection - off surface,
absorption - gives objects colour,
refraction - bending light.

Question 6

what does the pupil in the eye do?

Answer 6

lets light into the eye.

Question 7

what does the iris in the eye do?

Answer 7

contains muscles to control amount of light entering the eye.

Question 8

what does the sclera in the eye do?

Answer 8

forms the tough, protective wall of the eyeball to give it shape.

Question 9

what does the cornea in the eye do?

Answer 9

the transparent covering of the pupil and iris that refracts light.

Question 10

what do the extraocular muscles in the eye do?

Answer 10

move the eyeball, controlled by the oculomotor nerve.

Question 11

what does the optic nerve do?

Answer 11

carries axons from the retina to the brain.

Question 12

what does the optic disk do?

Answer 12

it is the blind spot - the origin of blood vessels and the optic nerve.

Question 13

what is the Macula in the eye?

Answer 13

region of retina for central vision - high visual acuity.

Question 14

what is the Fovea in the eye?

Answer 14

the centre of the Macula - highest visual acuity.

Question 15

what is the retina in the eye?

Answer 15

contains the sensory receptor cells and afferent neurons.

Question 16

what is the lens in the eye?

Answer 16

suspended by suspensory ligaments attached to ciliary muscle.

Question 17

how are images formed? (simple)

Answer 17

light rays must be focused on the retina, ideally the fovea.

Question 18

the degree of refraction is determined by:

Answer 18

differences in refractive indices between two media (such as air and the cornea, or the aqueous humour and the lens),
angle at which light hits the interface between these two medias.

Question 19

describe refraction by the cornea:

Answer 19

light arrives at the cornea,
light travels slowly through the water of the cornea allowing refraction to occur,
light that hits the cornea directly perpendicular moves straight on to the retina.

Question 20

define focal distance:

Answer 20

distance form refractive surface to convergence of parallel light rays.

Question 21

describe accommodation by the lens, for distant objects:

Answer 21

the light rays are pretty much parallel and the cornea provides sufficient refraction to focus the image on the retina.

Question 22

describe accommodation by the lens, for closer objects:

Answer 22

light rays aren’t that parallel so requires additional refraction to focus image on the retina, provided by the fattening of the lens.

Question 23

what is emmetropia?

Answer 23

when vision is happening correctly.

Question 24

what is hyperopia?

Answer 24

‘far-sightedness’ - we can see distant objects well but cannot refract near objects to form a clear object.

Question 25

what lens improves hyperopia and why?

Answer 25

a convex glass lens can help refract light enough so the image forms on the retina.

Question 26

what is myopia?

Answer 26

‘near-sightedness’ - we can see close objects but refraction happens too much to form a clear image of a far object.

Question 27

what lens improves myopia and why?

Answer 27

a concave glass lens will make light rays less parallel so that there is a normal amount of refraction on to the retina.

Question 28

what cells must light pass through before it reaches the photoreceptors?

Answer 28

ganglion cells and bipolar cells.

Question 29

what are photoreceptors in the retina?

Answer 29

rods and cones - sensory transductors.

Question 30

what do horizontal cells do in the retina?

Answer 30

receive input from and sends output to photoreceptors,

sends input to bipolar cells.

Question 31

what do amacrine cells do in the retina?

Answer 31

they are in between bipolar and ganglion cells,

modulate synaptic activity.

Question 32

what do ganglion cells do in the retina?

Answer 32

can fire action potentials,

and receive output from retina.

Question 33

what do photoreceptors contain?

Answer 33

photopigments that absorb light.

Question 34

what are the properties of rod cells?

Answer 34

high concentration of photopigments,
enable low-light vision (isotopic),
have low visual acuity / resolution.

Question 35

what are the properties of cones?

Answer 35

day-time vision (photopic),
enable colour vision,
high visual acuity / resolution,
have higher sensitivity.

Question 36

what are the properties of the central retina?

Answer 36

there is low convergence,
low sensitivity,
higher resolution.

Question 37

what are the properties of the peripheral retina?

Answer 37

high convergence,
high sensitivity,
low resolution.

Question 38

what does high convergence in the retina mean?

Answer 38

lots of rods and cones on one bipolar cell, but cannot identify which photoreceptor / which part is being activated.