Cambridge International A Level Biology Revision Guide

Cambridge International A Level Biology
Pressure was applied to the Pacinian corpuscle and recordings made of the electrical activity in the axon at
microelectrodes A and B. The results are shown in the diagram below.
recordings from microelectrode A recordings from microelectrode B
40
40
Light
pressure
20
Potential difference
0
across membrane / mV
–20
–40
20
0
–20
–40
–60
40
1 2 3
–60
40
1 2 3
20
20
Medium
pressure
Potential difference 0
across membrane / mV
–20
–40
0
–20
–40
362
–60
60
1 2 3
–60
60
1 2 3
40
40
20
20
Heavy
pressure
0
Potential difference
across membrane / mV
–20
–40
–60
0
–20
–40
–60
–80
1 2 3
Time / ms
–80
1 2 3
Time / ms
a Suggest what happened in the unmyelinated region of the axon as pressure was applied to the
Pacinian corpuscle. [4]
b Explain the pattern of recordings from microelectrode B as the pressure applied to the corpuscle
was increased. [4]
c Explain why sensory neurones from Pacinian corpuscles are myelinated and not unmyelinated. [3]
[Total: 11]