6.2 - Nervous coordination

Question 1

Explain what resting potential means and describe how it is maintained

Answer 1

• more + ions (Na+ and K+) outside compared to inside neurone
• so more - inside neurone: -70mV
• sodium-potassium pump: 3 Na+ out, 2 K+ in via active transport
• electrochemical gradient
• membrane more permeable to K+ than Na+ ions

Question 2

How do larger stimuli affect action potentials?

Answer 2

increase FREQUENCY of action potentials

Question 3

Why is the refractory period important?

Answer 3

• to ensure discrete, separate, distinguishable impulses produced
• to ensure action potentials travel in one direction: if two directions, response prevented
• limits frequency of impulse transmission to prevent overreaction to stimulus and overwhelming of senses

Question 4

What happens in the refractory period?

Answer 4

sodium voltage gated channels are closed and cannot be opened

Question 5

Name the 3 factors which affect the speed of conductance

Answer 5

• myelination (saltatory conduction)
• axon diameter
• temperature

Question 6

What is saltatory conduction in myelinated neurones and why is it a benefit?

Answer 6

• action potential jumps from node to node of Ranvier
• so faster travel along axon
• as doesn’t have to generate action potential along entire length of axon like in unmyelinated

Question 7

Why does a wider axon diameter increase speed of conductance?

Answer 7

less leakage of ions so action potentials travel faster

Question 8

Why does a higher temperature increase speed of conductance?

Answer 8

• ions diffuse faster
• respiratory enzymes work faster so more ATP for active transport in sodium-potassium pump

Question 9

Describe how an action potential travels down an unmyelinated neurone

Answer 9

• depolarisation of axon membrane causes formation of local currents
• sodium voltage gated channels open, Na+ ions diffuse in
• so adjacent region also depolarises

Question 10

Describe the steps in the generation of an action potential

Answer 10

• stimulus causes Na voltage gated channels to open
• axon more permeable to Na+ ions
• Na+ ions diffuse into axon down electrochemical gradient
• axon membrane depolarised
• if -55mV threshold reached, more sodium voltage gated channels open
• +40mV reached and repolarisation starts
• Na voltage gated channels close and K voltage gated channels open
• K+ ions diffuse out of neurone down conc gradient, eventually restoring resting potential
• hyperpolarisation occurs before this as the closing of K voltage gated channels is slightly delayed
• sodium-potassium pump returns P.D. to -70mV (resting potential)