Organisms Respond to their Changes in their Internal and External Environments: Nervous Coordination - Nerve Impulses, Speed of Conductance

Question 1

What factors affect the speed of a nerve impulse?

Answer 1

• Myelination and saltatory conduction
• Axon diameter
• Temperature

Question 2

How does temperature affect the speed of a nerve impulse?

Answer 2

• As temperature increases (up to 40°C), speed of conduction increases
• Ions have more kinetic energy so diffuse faster
• Above 40°C protein channels and pumps denature so speed decreases

Question 3

How does axon diameter affect the speed of a nerve impulse?

Answer 3

• The wider the diameter, the higher the speed of a nerve impulse
• Axons with wider diameters have less resistance to diffusion of Na⁺ ions into and along the axon

Question 4

How does myelination affect the speed of a nerve impulse?

Answer 4

• Myelinated fibres conduct faster than unmyelinated fibres

Question 5

Explain what happens during saltatory conduction

Answer 5

• Depolarisation only occurs at nodes of Ranvier
• Impulse jumps from node to node

Question 6

How do action potentials pass along non-myelinated neurones?

Answer 6

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