6- Receptors =)

Question 1

Describe how a Pacinian corpuscle produces a generator potential when stimulated. (3)

Answer 1

• ↑ pressure deforms stretch-mediated Na+ channels
• Na+ in
• depolarisation (–> g.p.)

Question 2

The membrane potential at the sensory neurone was the same whether medium or heavy pressure was applied to the finger tip (Pacinian corpuscle).
Explain why. (2)

Answer 2

• threshold reached
• causes maximal response/ all or nothing principle

Question 3

When an image is focussed on the fovea, the person sees the object in colour.
Explain why. (3)

Answer 3

• colour detected by cone cells
• fovea only has cone cells
• 3 types of cones- each sensitive to diff λ

Question 4

Explain why vision using the fovea has high visual acuity. (1)

Answer 4

each cone connected to separate neurone, rods in other parts share a neurone

Question 5

Explain why vision using other parts of the retina has high sensitivity to light. (3)

Answer 5

• many rods in other parts
• rhodopsin v sensitive to light
• rods connected in groups to ganglion cell
• summation
• if enough light > threshold hits any cell in the group, nervous impulses to brain along optic nerve

Question 6

Explain waht causes vision using the fovea to be in colour. (1)

Answer 6

3 diff types of cone cells- sensitive to diff λ

Question 7

Cone cells give higher visual acuity than rod cells.
Explain how. (2)

Answer 7

• each cone cell- separate neurone to brain/ ganglion cell
• x retinal convergence/ x summation

Question 8

Complete achromatopsia is a form of complete colour blindness. It is caused by having only rods and no functional cone cells.
People with complete achromatopsia have difficulty in seeing detail.
Explain why. (3)

Answer 8

• no functional cones
• each cone connected to single neurone
• send separate impulses to brain