Speed of Conductance

Question 1

What three factors affect the speed of conductance/an action potential?

Answer 1

• myelination and saltatory conduction
• axon diameter
• temperature

Question 2

What is an axon?

Answer 2

a long, conductive fibre that carries the nervous impulse along the motor neuron

Question 3

What forms the myelin sheath?

Answer 3

Schwann cells

Question 4

What about the Schwann cells makes them insulators?

Answer 4

they are lipids

Question 5

What is saltatory conduction?

Answer 5

the action potential jumping/moving from node to node

Question 6

why does the myelin sheath speed up conductance?

Answer 6

as action potentials only have to be generated in a limited number of spaces, not along the whole length of the axon

Question 7

How does a wider diameter impact the speed of conductance?

Answer 7

will make it faster

Question 8

Why does a wider diameter speed up conductance?

Answer 8

it means that there is less leakage of ions

Question 9

Why does a higher temperature increase speed of conductance?

Answer 9

• rate of diffusion increases
  -enzymes involved in respiration act faster so more ATP for co-transport

Question 10

Why would no myelin sheaths lead to slower responses?

Answer 10

• cannot ‘jump’ from node to node
• more depolarisation over a greater length

Question 11

How does the myelin sheath impact speed of conductance?

Answer 11

• myelin sheath increases speed of conductance
• schwann cells cause insulation around an area of the axon
• depolarisation cannot occur in insulated areas, only in the nodes of Ranvier
• saltatory conduction

Question 12

How does temperature impact speed of conductance?

Answer 12

• high temperature increases speed of action potentials
• higher temperature increases diffusion up until a point
• enzymes involved in respiration
• above a certain point enzymes/proteins denature and APs cease

Question 13

What is the All or Nothing principle?

Answer 13

• threshold value (-55mV)
• below the threshold, no AP regardless of strength
• stimulus above threshold will generate an action potential
• all action potentials are the same size

Question 14

Why might damage to the myelin sheath of neurones cause muscular paralysis?

Answer 14

• no saltatory conduction/Depolarisation occurs along whole length
• impulses slowed/stopped
• do not reach/take longer to reach neuromuscular junction