Action Potential

Question 1

what is action potential?

Answer 1

• occurs when neurons are electrically stimulated.
• Is a reversal of the resting potential
• Na+ and K+ ion channels are open and close depending upon the voltage

Question 2

what main 3 phases does action potential have?

Answer 2

• Repolarisation
• Deporalisation
• Hyperpolarisation

Question 3

What happens during depolarisation?

Answer 3

• Negative inside the cells at resting potential
• when neuron is stimulated, voltage becomes more positive
• Na+ channels open and flood into the neuron down their concentration gradient
• making it positive inside the cell

Question 4

What happens during repolarisation?

Answer 4

• Voltage gated Na+ close again
• The K+ channels open and allow K+ to go out of the cell, making it negative again

Question 5

What happens during hyperpolarisation?

Answer 5

• Too many k+ leave the cell
• this drops the voltage past resting potential (-70mV) to (-90mV)
• K+ channels close at this voltage
• resting potential is re-established by the Na+K+ pump to bring it back to -70mV
• THIS IS THE REFRACTORY PERIOD
• Ensures no overlapping of action potentials and that they can only travel in one direction

Question 6

What is stage one of action potentials? - stimulus

Answer 6

• STIMULUS
• excites the neuron cell membrane
• Na+ ion channels open
• sodium diffuses into the neuron down the sodium ion electrochemical gradient
• as the membrane is now more permeable to sodium
• makes the inside of the neuron less negative

Question 7

What is stage two of action potentials? - Depolarisation

Answer 7

• if potential difference reaches the threshold (around -55mV)
• voltage gated ion channels open
• more sodium diffuses into the neuron
• an example of positive feedback

Question 8

What is stage three of action potentials? - Repolarisation

Answer 8

• potential difference around +30mV
• sodium ion channels close
• voltage gated potassium channels open
• membrane becomes more permeable to potassium
• potassium ion channels diffuse out
  of neuron and down the potassium ion concentration gradient
• gets the membrane back to resting potential
• THIS IS NEGATIVE FEEDBACK

Question 9

What is stage four of action potentials? - Hyperpolarisation

Answer 9

• potassium ion chennsl are too slow to close
• there is a REFRACTION - too many potassium ions diffuse out of the neurone
• potential difference becomes more negative at resting potential

Question 10

What is stage five of action potentials? - Resting potential

Answer 10

• ion channels reset
• sodium-potassium pump returns the membrane to resting potential
• maintains it until the membrane is excited by another stimulus

Question 11

What happens if the membrane potential becomes more positive than its resting potential?

Answer 11

• membrane is said to be polarised

Question 12

What happens if the membrane potential becomes more negative than its resting potential?

Answer 12

• membrane is said to be depolarised

Question 13

What happens if there is a difference in charge (a potential difference/voltage) across a membrane?

Answer 13

• membrane is said to be hyperpolarised