Nervous tissue

Question 1

Describe a neurone’s resting potential. (5 points)

Answer 1

• When a neurone is not transmitting an action potential
• The inside is more negative -65mv
  -This is achieved by the sodium potassium pump
• The neurone membrane is more permeable to K+ than Na+
• Pump sets up a concentration gradient with more sodium ions outside the neurone and more potassium ions inside

Question 2

What does the sodium potassium pump do?

Answer 2

Pumps 3 Na+ (sodium) ions out of the neurone for every 2 K+ (potassium) inside the neurone.

Question 3

Describe a neurone’s action potential. (3 points)

Answer 3

• This is when a stimulus acts on a neurone and causes sodium ion channels in the neurone membrane to open up.
• Sodium ions then diffuse into neurone due to previous concentration gradient set up.
• This causes membrane potential to become less negative than -60mv. This is known as the generator potential.

Question 4

Describe a depolarisation during the action potential in a neurone. (4 points)

Answer 4

-If generator potential reaches -50mv, which is known as threshold potential, Na channels will start to open up.
- This causes more sodium ions to flood into the neurone.
- Membrane potential reaches +40mv.
- This must be reversed so sodium ion channels close and potassium ion channels open up.

Question 5

Describe repolarisation during the action potential in a neurone. (1 point)

Answer 5

• Due to there being more potassium ions in the neurone, potassium ions diffuse out. This returns the membrane back to a negative value.

Question 6

Describe hyperpolarisation during the action potential in a neurone. (3 points)

Answer 6

• The membrane potential can become more negative than at resting potential.
• This occurs because too many potassium ions leave the neurone.
• The sodium potassium pump ensures the resting potential of 60mv is restored.

Question 7

Describe the refractory period in a neurone. (3 points)

Answer 7

• After an action potential sodium and potassium ions are in the wrong place.
• The concentration of these ions must be restored by the Na+/K+ pump.
• Therefore, this is the time after the action potential where another action potential cannot b e generated. This is to ensure the action potentials go in one way along a neurone.

Question 8

What is the order of events in a neurone starting from the resting potential?

Answer 8

Resting potential, action potential which during the neurone goes through depolarisation, repolarisation and then hyperpolarisation, and then lastly the refractory period.

Question 9

What is a neurone?

Answer 9

A nerve cell.