6.2 Receptors

Question 1

How is a Pacinian corpuscle structured?

Answer 1

Sensory neurone surrounded by lamellae (layers of connective tissue)

Question 2

How is a generator potential established in a Pacinian corpuscle?

Answer 2

• Pressure causes lamellae to stretch and deform
• So stretch-mediated sodium ion channels open and Na+ diffuse into sensory neurone
• Greater pressure causes more sodium ion channels to open so more Na+ to enter
• This causes depolarisation
• If generator potential reaches threshold an action potential is triggered (all-or-nothing principle)

Question 3

Rods

Answer 3

Allow monochromatic vision (one pigment)
More sensitive to low light (several rods connected to one bipolar neurone so spatial summation to overcome threshold)
Lower visual acuity

Question 4

Cones

Answer 4

Allow colour vision (three different pigments absorb different wavelengths)
Less sensitive to low light
Higher visual acuity (each cone connected to one bipolar neurone so cones send separate impulses to the brain)