Rods and Cones

What is the pigment in rod cells?

Rhodopsin

What is the pigment in cone cells?

Iodopsin

What are the 3 types of cone cells?

• Cones sensitive to red light

• Cones sensitive to green light

• Cones sensitive to blue light

Why do rods have a high sensitivity/ can detect low levels of light

1. Multiple rod cells attached to one bipolar cell

2. Rhodopsin is broken down in each rod cell

3. Collectively the broken down rhodopsin creates a big enough stimulus to trigger an action potential (spatial summation)

Why do cone cells have a high visual acuity?

1. No retinal convergence

2. So action potential generated by each individual cell travels along its own optic nerve to the brain

What is the blind spot caused by?

1. Absence of photoreceptor cells

2. Where optic nerve joins to the retina

Why do rod cells have a low visual acuity?

Retinal convergence

What are the 2 reasons the cone cells having a low sensitivity

• Iodopsin is only broken down in a high light intensity, as low sensitivity to light

• No retinal convergence, so no spatial summation

Where are most cone cells distributed and why?

• Fovea

• Receives the highest intensity of light

• Cone cells only respond to high light intensities

Visual acuity

The ability to distinguish between 2 different sources of light