6.1.2 Receptors

Question 1

What features are common to all sensory receptors?

Answer 1

• Act as energy transducers which establish a generator potential
• Respond to specific stimuli

Question 2

Describe the basic structure of a Pacinian corpuscle

Answer 2

• Single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule
• Stretch-mediated sodium channels on plasma membrane
• Capillary runs along base layer of tissue

Question 3

What stimulus does a Pacinian corpuscle respond to? How?

Answer 3

1. Pressure deforms membrane, causing stretch-mediated sodium ion channels to open
2. If influx of sodium ions raises membrane to threshold potential, a generator potential is produced
3. Action potential moves along sensory neuron

Question 4

Name the 2 types of photoreceptor cell located in the retina

Answer 4

Cone and Rod cells

Question 5

Where are rod and cone cells located in the retina?

Answer 5

Rod: evenly distributed around periphery but not in central fovea
Cone: mainly central fovea
No photoreceptors at blind spot

Question 6

Compare rod and cone cell’s pigment

Answer 6

Rod: rhodopsin
Cone: 3 types of iodopsin (blue, red, green)

Question 7

Compare rod and cone cell’s visual acuity

Answer 7

Rod: low resolution - many rod cells synapse with 1 bipolar neuron
Cone: high resolution - 1 cone cell synapses with 1 bipolar neuron = no retinal convergence

Question 8

Compare rod and cone cell’s colour sensitivity

Answer 8

Rod: monochromatic - all wavelengths of light detected
Cone: Tricolour - red, blue, green wavelengths absorbed by different types of iodopsin

Question 9

Compare rod and cone cell’s light sensitivity

Answer 9

Rod: very sensitive - spatial summation of subthreshold impulses
Cone: less sensitive - not involved in night vision

Question 10

Outline the pathway of light from a photoreceptor to the brain

Answer 10

photoreceptor –> bipolar neuron –> ganglion cell of optic nerve –> brain