Organisms Respond to Changes in their Internal and External Environments: Nervous Coordination - Nerve Impulses, Passage of Action Potentials

Question 1

What causes waves of depolarisation?

Answer 1

• When action potentials occur, some Na+ ions that enter the neurone diffuse sideways
• This causes Na+ ion channels in next region of neurone to open and sodium ions diffuse into that part
• Causes wave of depolarisation

Question 2

Why does the wave of depolarisation move away from parts of membrane in refractory period?

Answer 2

• These parts can’t fire an action potential and can’t be depolarised
• Na+ channels closed in these areas

Question 3

How do action potentials pass along non-myelinated neurones?

Answer 3

• Impulse travels as wave along whole length of axon membrane
• Depolarisation occurs whole length of axon membrane

Question 4

How do action potentials pass along myelinated neurones?

Answer 4

• Depolarisation only occurs at nodes of Ranvier (where Na+ ions can get through membrane)
• Impulse jumps from node to node
• This is called saltatory conduction

Question 5

Do action potentials travel faster along non-myelinated or myelinated neurones?

Answer 5

• Myelinated neurones