Nerve impulses

Question 1

How is a resting potential set up and maintained?

Answer 1

3 sodium ions pumps out of neurone
2 potassium ions pumped into neurone
By sodium potassium pump
Potassium ions diffuse out of neurone
Sodium ions unable to diffuse into neurone

Question 2

Define resting potential?

Answer 2

The potential across the plasma membrane of a cell that is not conducting an impulse.

Question 3

Which type of transport is used by the sodium potassium pump?

Answer 3

Active transport

Question 4

When a resting potential is set up which side of the membranes is
more positively charged?

Answer 4

Outside the neurone is more positively charged than the inside of the membrane

Question 5

Describe what happens when an action potential is produced.

Answer 5

Sodium ion channel proteins open
Sodium ions diffuse through the membrane into the neurone
Potassium ion channel close.
Inside of axon becomes more positively charged.

Question 6

Name the process that causes an action potential to be produced.

Answer 6

Depolarisation

Question 7

What does repolarisation mean?

Answer 7

Membrane becomes polarised again
Resting potential is established

Question 8

Describe what happens during repolarisation

Answer 8

Sodium ion channels close
Potassium ion channels open
Potassium ions diffuse out of the neurone

Question 9

What is the refractory period?

Answer 9

The period of time after an action potential when a neurone cannot produce a second action potential as the membrane is not sufficiently polarised.

Question 10

How does the neurone respond to a bigger stimulus?

Answer 10

More frequent action potentials produced.

Question 11

Sodium and potassium ions can only cross the axon membrane through proteins. Explain why.

Answer 11

Polar ions
Cannot pass through hydrophobic phospholipid membrane

Question 12

What is the voltage across the membrane at resting potential?

Answer 12

-70mV

Question 13

What happens if the threshold (around -55mV) is reached?

Answer 13

Depolarisation occurs
More sodium ion channels open
Sodium ions diffuse into neurone

Question 14

Why does hyperpolarisation occur?

Answer 14

Potassium ion channels slow to close
Too many potassium ions diffuse out of neurone

Question 15

Name 2 factors that affect the speed of impulses and describe their effect.

Answer 15

Temperature - Higher temperature –> faster impulse transmission as ions diffuse faster.
Diameter of axon- wider axon –> faster speed of conduction
Myelination - increases impulse speed due to saltatory conduction

Question 16

What is saltatory conduction?

Answer 16

Action potential jumps between Nodes of Ranvier
Faster conduction of impulses
Occurs on myelinated neurones

Question 17

Give one function of the refractory period

Answer 17

Produces discrete impulses that are unidirectional

Question 18

Describe a motor neurone

Answer 18

Dendrites to carry electrical impulse from synapse to cell body
Cell body containing the nucleus and cell organelles
Axon to transmit electrical impulse to the effector

Question 19

Describe the structure and function of the Schwann cells

Answer 19

Wrap round axon many times
Made from myelin rich membranes
Insulates the axon
Nodes of Ranvier - short gaps between neighbouring Schwann cells where there is no myelin sheath. Allow saltatory conduction

Question 20

What is the ‘all or nothing’ principle?

Answer 20

Any stimulus that causes the membrane to reach threshold potential will generate an action potential.
All action potentials have the same magnitude

Question 21

How does temperature affect speed of conductance?

Answer 21

Faster rate of diffusion of ions
Faster rate of respiration releases more ATP for active transport to re-establish resting potential.
High temperature ruptures cell membrane and denature enzymes/protein carriers/channels