Nerve impulses: action potentials 5.3.3

Question 1

What is an action potential?

Answer 1

A brief reversal of the potential across the membrane of a neurone causing a peak of +40mv compared to the resting potential of -60mv

Question 2

What do the membranes of specialised cells in the nervous system contain?

Answer 2

• Sodium ion (Na+) channels & potassium ion (K+) channels which are gated
• Sodium/potassium pumps which actively pump sodium ions out and potassium ions into the cell
• 3 sodium ions are pumped out, for every 2 potassium pumped into the cell

Question 3

Describe the neurone at rest

Answer 3

• Na+ and K+ channels are closed
• Resting membrane potential: -60mv
• Na+ and K+ pumps aid this

Question 4

Describe the neurone at its threshold potential

Answer 4

• Sodium (Na+) channels open.
• If the threshold is reached, more Na+ gates open (generator potentials)
• Action potential is triggered
  -50mv

Question 5

Describe the neurone during depolarisation

Answer 5

• Na+ channels open
• K+ channels closed
• Na+ rushes into cell and inside becomes positive
  +40mv

Question 6

Describe the neurone during repolarisation

Answer 6

• Na+ channels close
• K+ channels open
• K+ leave the cell and the inside becomes more negative

Question 7

Descibe the neurone during hyperpolarisation

Answer 7

• Na+ channels closed but the slower K+ channels remain open - and the K+ ions leak out
• Becomes more negative than at rest

Question 8

How is the resting rate restored?

Answer 8

By the Na+/K+ pumps

Question 9

How does the sodium potassium pump work?

Answer 9

It uses the energy from ATP, splitting to simultaneously pump 3 sodium ions out and 2 potassium ions in.
This results in the inside being more negative as there are also many negative ions within it.
Creating a POTENTIAL DIFFERENCE!