Potentials

Question 1

Explain how the resting potential of –70 mV is maintained in the sensory neurone
when no pressure is applied.

Answer 1

1. Membrane more permeable to potassium ions
   and less permeable to sodium ions;
2. Sodium ions actively transported/pumped out
   and potassium ions in;

Question 2

Explain how applying pressure to the Pacinian corpuscle produces the changes in
membrane potential recorded by microelectrode P.

Answer 2

1. (Pressure causes) membrane/lamellae to
   become deformed/stretched;
2. Sodium ion channels in membrane open and
   sodium ions move in;
3. Greater pressure more channels open/sodium
   ions enter;

Question 3

The membrane potential at Q was the same whether medium or heavy pressure
was applied to the finger tip. Explain why

Answer 3

1. Threshold has been reached;
2. (Threshold or above) causes a maximal response
   / all or nothing principle;

Question 4

Multiple sclerosis is a disease in which parts of the myelin sheaths surrounding
neurones are destroyed. Explain how this results in slower responses to stimuli.

Answer 4

1. Less/no saltatory conduction / action
   potential/impulse unable to ‘jump’ from node to
   node;
2. More depolarisation over length/area of
   membranes;

Question 5

Define nerve impulse

Answer 5

self-propagating wave of electrical energy that travels down axon membrane

Question 6

Name the resting potential in humans

Answer 6

-65mV

Question 7

Describe how the resting potential is established

Answer 7

S/K pump actively transports Na+ out at a greater rate of P+ in. 3 Na+ for 2K+
Electrochemical gradient due to move Na+ outside than inside axon. Vice versa with K+

Question 8

Describe how the action potential is established

Answer 8

Stimulus detection causes a temporary reversal of charges above the threshold
Na+ voltage-gated channel open so Na+ enter the axon down their con. gradient
This causes a positive feedback mechanism along the axon
The axon becomes depolarise and the membrane potential reverses
Na+ channels close and K+ channels open
K+ leaves via electrochemical gradient
Hyperpolarization occurs
Na/K pump restores resting potential hence repolarisation

Question 9

Name the action potential in humans

Answer 9

40 mV

Question 10

Describe what an action potential is

Answer 10

A travelling wave of depolarisation

Question 11

How does the impulse travel down a myelinated neurone?

Answer 11

salvatory conduction ( faster)