3.6.1.2 Receptors

Question 1

What is a pacinian corpuscle?

Answer 1

Receptor in the skin which responds to pressure

• single sensory neurone wrapped in layers of connective tissue, channel proteins in plasma membrane

Question 2

What is a generator potential?

Answer 2

The change in potential difference due to a stimulus

Question 3

How does stimulation of the pacinian corpuscle cause an action potential?

Answer 3

• lamellae become deformed and press on sensory neurone ending
• membrane of sensory neurone stretches causing stretch mediated Na+ channels to open, increasing permeability to Na+
• Na+ ions diffuse into the cell creating a generator potential
• If depolarisation reaches threshold an action potential will be generated

Question 4

How do photoreceptors convert light into electrical impulses?

Answer 4

1. Light enters eye and hits photoreceptors
2. Light sensitive pigments in the membranes absorb light, causing them to be bleached and broken down
3. Membrane permeability to Na+ increases, more Na+ diffuses in
4. Generator potential created, if threshold reached, depolarisation is generated and transmitted to a bipolar neurone
5. Bipolar neurones transmit the impulse to the optic nerve, which takes the impulse to the brain

Question 5

Locations of photoreceptors in the retina

Answer 5

• Fovea - lots of cones - light is most concentrated here

- lots of rods in rest of retina

Question 6

Rod cells : pigment, colour, summation, visual acuity, sensitivity to light

Answer 6

• Rhodopsin
• Black and white
• Spatial summation
• Low visual acuity (many rod cells to 1 bipolar cells, can’t distinguish source/ which rod is stimulated)
• Very sensitive to light

Question 7

Cone cells : pigment, colour, summation, visual acuity, sensitivity to light

Answer 7

• Idopsin
• Trichromatic (red, green, blue)
• Temporal summation
• High visual acuity (one cone to one bipolar cell so can determine direction of light)
• Low sensitivity to light