the eye

Question 1

key features of ROD cells

• pigment
• sensitivity
• acuity

Answer 1

> monochromatic BECAUSE they contain 1 pigment
they are more sensitive to low light BECAUSE many rods join 1 neurone (spatial summation)
they have lower visual acuity because many rods join 1 neurone

Question 2

key features of CONE cells and why:

Answer 2

> cone cells enable colour vision BECAUSE they contain trichromatic pigments (RBG)
they are less sensitive to low light BECAUSE each cone has its own bipolar neurone –> stronger stimulus needed to reach threshold
they have high visual acuity BECAUSE each cone has its own bipolar neurone

Question 3

describe how an action potential is triggered by light:

Answer 3

• the lens focusses light onto the retina
• pigments in the photoreceptors absorb the light
• causing some Na+ channels to OPEN (leading to slight depolarisation of membrane which = the generator potential)
• if the generator potential reaches threshold, an action potential is triggered