13.3 Sensory receptors

Question 1

Features of sensory receptors

Answer 1

Specific to a single type of stimulus
Act as a transducer - convert stimulus into nerve impulse

Question 2

Mechanoreceptor

Answer 2

Stimulus - pressure and movement
Eg - Pacinian corpuscle

Question 3

Chemoreceptor

Answer 3

Stimulus - chemicals
Eg - Olfactory receptor

Question 4

Thermoreceptor

Answer 4

Stimulus - heat
Eg - end bulbs of Krause

Question 5

Photoreceptors

Answer 5

Stimulus - light
Eg - cone cell

Question 6

Sensory receptors as transducers

Answer 6

Sensory receptors detect stimuli
Stimulus converted into nervous impulse (generator potential)

Question 7

Structure of Pacinian corpuscle

Answer 7

End of sensory neurone is found in the centre of the corpuscle
Surrounded by layers of connective tissue
Each layer of tissue is separated by a layer of gel

Question 8

How does a Pacinian corpuscle convert mechanical pressure into a nervous impulse?

Answer 8

1) In its resting state, stretch mediated sodium ion channels in the sensory neurone’s membrane are too narrow to allow Na+ ions to pass through (resting potential)
2) Pressure applied, corpuscle changes shape and membrane surrounding neurone stretches
3) Membrane stretches, so Na+ channels widen and Na+ can diffuse in
4) Influx of Na+ changes potential of the membrane - becomes depolarised, creating a generator potential
5) Generator potential creates an action potential that passes along the sensory neurone