3.6.2.1 nerve impulses

Question 1

What is the voltage across the membrane at resting potential?

Answer 1

-70mV

Question 2

How is resting potential maintained?

Answer 2

Sodium potassium pumps transports 3 sodium ions out of the neurone for every 2 potassium ions that are transported in. The membrane is impermeable to sodium and permeable to potassium.

Question 3

What happen in response to the stimulus to make the inside of the neurone less negative?

Answer 3

Sodium channels open. Sodium diffuses into the neurone down the electrochemical gradient.

Question 4

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

Answer 4

Depolarisation occurs. More sodium channels open, sodium diffuses rapidly into the neurone.

Question 5

At what potential difference do sodium channels close?

Answer 5

+30mV

Question 6

After depolarisation, how does the neurone return to resting potential?

Answer 6

Sodium channels close and potassium channels open. Potassium diffuses out of the neurone.

Question 7

Why does hyperpolarisation occur?

Answer 7

The potassium ion channels are slow to close so there’s a slight overshoot where too many potassium ions diffuse out of the neurone.

Question 8

What is the refractory period?

Answer 8

The period of time after an action potential when the neurone can’t be excited.

Question 9

How does the nuerone respond to a bigger stimulus?

Answer 9

Action potentials will occur more frequently.

Question 10

During an action potential, the membrane potential rises to +40 mV and then falls. Use information from the graph to explain the fall in membrane potential.

Answer 10

Potassium channels open;

Potassium out;

Sodium channels close;

Question 11

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

Explain why.

Answer 11

can not pass through phospholipid bilayer;
because water soluble / not lipid soluble / charged / hydrophilic /
hydrated;

Question 12

Explain the importance of reflex actions.

Answer 12

1. automatic (adjustments to changes in environment) / involuntary;
2. reducing / avoiding damage to tissues / prevents injury / named injury
   e. g. burning;
3. role in homeostasis / example;
4. posture / balance;
5. finding / obtaining food / mate / suitable conditions;
6. escape from predators;

Question 13

Give two differences between a cholinergic synapse and a neuromuscular junction.

Answer 13

neurone to neurone and neurone to muscle;
action potential in neurone and no action potential in muscle /
sarcolemma;
no summation in muscle;
muscle response always excitatory (never inhibitory);
some neuromuscular junctions have different neurotransmitters;