chpt 10 eye

Question 1

What are the to types of photoreceptors and what do they do ?

Answer 1

1. rod cells
   low light intensity
   photosensitive pigment is visual purple
   when exposed to light, visual purple breaks down and reforms in absence of light
   roughly 30min to visual purple to reform as it gets destroyed faster in bright light than being reformed in dim light
2. cone cells
   higher light intensity and differences in wavelength
   3 types of cone -> red green blue
   fovea has highest conc of cone cells but no rod cells

Question 2

What happens to the eye in bright light ?

Answer 2

circular muscles of iris contract
radial muscles of iris relax
pupil diameter decreases
less light enters eye

Question 3

What happens to the eye in dim light ?

Answer 3

1. circular muscles of iris relax
2. radial muscles of iris contract
3. pupil diameter increases
4. more light enters eye

Question 4

How is an image formed ?

Answer 4

1. light rays from object are refracted when they pass through the cornea and aqueous humour onto the lens
2. light rays further refracted by lens onto retina
3. stimulates rod (low) or cone (high) depending on light intensity
4. image formed is vertically inverted, laterally reversed and diminished
5. impulses generate when light falls onto retina and these impulses and transmitted via optic nerve to brain so we can see correctly

Question 5

What is the role of brain in vision ?

Answer 5

1. nerve impulses are transmitted to the optic centre of the brain via the optic nerve
2. brain interprets info and formed an upright image
3. if blind has his sight restored, they will temporarily see upside down
4. brain can interpret information from overlapping visual fields from both eyes and interprets them a one image

Question 6

What happens when someone focuses on a distant object after seeing a close one ?

Answer 6

1. parallel light rays from distant object enters eye
2. ciliary muscles relax
3. suspensory ligament becomes taut
4. lens become thinner
5. photoreceptors -> nerve impulses -> brain -> can see distant object

Question 7

What happens when a person focusses on a close object after seeing a distant one ?

Answer 7

1. diverging light rays from close object enters eye
2. ciliary muscle contract
3. suspensory ligaments slacken
4. lens becomes thicker
5. photoreceptors -> nerve impulses -> brain’s optic centre -> can see close object