vision

Question 1

the iris - amount of light

Answer 1

donut shaped band of tissue which regulates the amount of light that reaches the retina by adjusting the size of the pupil

Question 2

Pupil dilation/ constriction

Answer 2

Dilation - the iris relaxes - sensitivity is improved, acuity is poor
Constriction - iris contracts , acuity is improved

Question 3

the cornea- focusing the image

Answer 3

covers the front of the eye and works with the lens to focus incoming light

Question 4

the lens - focusing

Answer 4

held in place nu suspensory ligaments called zonules.

Changes shape by a process of accommodation

Question 5

Accommodation - the lens

Answer 5

A rounder thicker lens - bends light more (near objects)

A flatter lens- bends light less (far objects)

Question 6

The retina - transduction

Answer 6

Thin sensitive tissue at the back of the eye, contains a layer of photoreceptor cells.

Question 7

The macula - transduction

Answer 7

the centre of the retina is the macula

- VERY high concentration of photoreceptor cells

Question 8

The fovea

Answer 8

The centre of the macula- sharpest vision.

• no rods only cones
• blood vessels and other cells are displaced to the sides

Question 9

Rods

Answer 9

best in dim light

Very few around the fovea - why stars disappear when you look directly at them.

Question 10

The optic disc - the blind spot

Answer 10

Where GANGLION cell axons leave the retina
there are no photoreceptors
the brain uses completion to fill in the gap.

Question 11

the sclera

Answer 11

white of the eye - protective layer

Question 12

the choroid

Answer 12

a layer of tisse between the retina and sclera

contains many blood vessels and is critical for providing o2 and glucose to the retinal cells

Question 13

tapetum lucidum

Answer 13

animals have a reflective tusse

Question 14

What are the three layers of the retina

Answer 14

1. photoreceptors
2. bipolar cells
3. retinal ganglion cells

Question 15

photoreceptors

Answer 15

Rods and cones.
Rods: Rhodopsin inactive, sodium channels are kep open by cyclic GMP , cell is depolarised. Rods release glutamate

Cones: Rhodopsin activates, cyclic GMP is broken down, sodium channels close, cell is hyperpolarised, glutamate reduced.

Question 16

what is scotopic vision

Answer 16

dim light (Rods)

Question 17

do rods have high or low convergence

Answer 17

rods have high convergence: Many to 1 = results in poor acuity but good sensitivity

Question 18

do cones have high or low convergence

Answer 18

Cones have low convergence: 1 to 1= results in good acuity but poor sensitivity.

Question 19

deuteranomoly

Answer 19

form of colour blindness where the sensitivity of the green cones is shifter towards the red.

Question 20

saccades

Answer 20

the eye continually scans the visual field so information can be integrated

Question 21

bipolar cells

Answer 21

process input from the photoreceptors and output to retinal ganglion cells

allow some low level signal processing (aided by interneurons: horizontal and amacrine cells)

photoreceptors converge via bipolar cells to retinal ganglion cells (few to 1 for cones, many to 1 for rods)

Question 22

retinal ganglion cells

Answer 22

Facilitate the detection of edges.

Either on centre off surround or off centre on surround= This means that edges can be detected.

Question 23

Horizontal cells

Answer 23

mediate the detection of mach bands.

when activated they inhibit other cells which creates a bigger difference between areas of high and low illumination