3.6.1.2 Receptors

Question 1

Describe the basic structure of a pacinian corpuscle

Answer 1

lamellae
sensory neurone ending
sensory neurone axon
myelin sheath
stretch mediated sodium ion channel
gel

Question 2

describe how a generator potential is established in a pacinian corpuscle

Answer 2

1) mechanical stimulus deforms lamellae and stretch mediated sodium ion (Na+) channels
2) So Na+ channels in membrane open and Na+ diffuse into sensory neurone
- greater pressure caused more Na+ channels to own and more Na+ to enter
• This cause’s depolarisation, leading to a generator potential
- if generator potential reaches threshold it triggers an action potential

Question 3

explain what the pacinian corpuscle illustrates

Answer 3

• receptors respond only to specific stimuli
- pacinian corpuscle only responds to mechanical pressure
• stimulation of a receptor leads to the establishment of a generator potential
- when threshold is reached , action potential sent

Question 4

explain the differences in sensitivity to light for rods and codes in the retina

Answer 4

rods are more sensitive to light :
•several rods connected to a single neurone
• spatial summation to overcome threshold to generate an action potential
Cones are less sensitive to light :
• each cone connected to a single neurone
• no spatial summation

Question 5

Explain the differences in visual acuity for rods and cones in the retina

Answer 5

rods give lower visual acuity :
• several rods connected to a single neurone
• so several rods send a single set of impulses to brain (so can’t distinguish between separate sources of light )
Comes give higher visual acuity :
• each cone connected to a single neurone
• comes send separate impulses to brain ( so can distinguish between 2 separate sources of light )

Question 6

explain the differences in sensitivity to colour for rods and cones in the retina

Answer 6

rods allow monochromatic vision :
• 1 type of rod / 1 pigment
Cones allow colour vision :
• 3 types of cones - red , green and blue sensitive
• with different optical pigments - absorb different wavelengths
• stimulating different combinations of cones gives range of colour perception