6. Action Potentials

Question 1

name the five stages of an action potential

Answer 1

1. Stimulus
2. Depolarisation
3. Repolarisation
4. Hyperpolarisation
5. Resting potential

Question 2

an action potential causes a wave of ————

Answer 2

depolarisation

Question 3

what is the period after an action potential called?

Answer 3

Refractory period

Question 4

what is a refractory period?

Answer 4

the time after an action potential is fired when another action potentil cannot be fired

Question 5

what do refractory periods mean?

Answer 5

• keeps impulses unidirectional
• produces discrete impulses
• produces a time delay between action potentials

Question 6

describe the processes involved in action potentials

Answer 6

1. Stimulation:
   - the neurone is excited
   - NA+ ions diffused down the electrochemical gradient
   - membrane becomes more permeable to NA ions and less negative
2. Depolarisation:
   - if the threshold is reached an action potential is fired
   - voltage-gatage sodium channels open, absorbing more NA
   - this sodium influx causes it to become positive on inside and negative on outside
3. Repolarisation:
   - when PD reaches 30Mv, sodium voltage gatage channels lose and potassium ones open
   - means membrane is more permeable to potassium
   - 3K leaving 2Na entering the cell
   - reducing the cell to become more negative
4. Hyperpolarisation:
   - due to more K+ ions leaving the cell and less sodium entering the cell via the potassium channels,
   - cell becomes negative on inside and positive on outside
5. Resting Potential:
   - the cells electrochemical gradient is restored
   - the cell is negative on inside and positive on outside

Question 7

action potentials are ___________

Answer 7

unidirectional