Nerve Impulse

Question 1

Explain the All or nothing principle

Answer 1

(If stimulus isn’t large enough)
If depolarisation doesn’t exceed -55mv (threshold)
Won’t provide enough energy to open enough NA ion channels to go above -55 = NO ACTION POTENTIAL + impulses not produced

IF DO REACH -55
Stimulus does trigger depolarisation to -55mv = action potential - WILL ALWAYS PEEK AT SAME MAX VOLTAGE (+40mv) - increased frequency of action potentials

Question 2

Why do depolarisation peak at +40mV

Answer 2

Volted gated NA ion channels will close when +40 reached inside axon
Not going to increase any further

Question 3

Explain repolarisation

Answer 3

Potassium ion channels opens at +40V
Twice amount of K ion diffusing out
Decrease in voltage = more negative
(More positive ions outside than inside)

Question 4

explain how a resting potential is maintained across the axon membrane of a neurone (3)

Answer 4

higher conc of potassium ions inside higher conc of sodium ions outside
membrane is less permeable to NA ions entering
NA ions actively transport out and K ions in

Question 5

explain why the speed of transmission is faster along a myelinated axon than a non- myelinated axon

Answer 5

myelin sheath provides electrical insulation
in myelinated there is depolarisation at the Nodes of Ranvier whereas in non- myelinated, depolarisation occurs along the whole length of the axon