nerve impluses

Question 1

Describe resting potential

Answer 1

Inside of axon has a negative charge relative to outside

Question 2

Describe the all-or-nothing principle

Answer 2

● for action potential to be produced, depolarisation must exceed threshold potential
● Action potentials produced are always same peak/magnitude at same potential
○ Bigger stimuli instead increase frequency of action potentia

Question 3

Passage of action potential in non mylenated axon

Answer 3

● Action potential passes as a wave of
depolarisation
● Influx of Na+ in one region increases
permeability of adjoining region to Na+ by
causing voltage-gated Na+ channels to open
so adjoining region depolarises

Question 4

Suggest how damage to the myelin sheath can lead to slow responses and /
or jerky movement

Answer 4

● Less / no saltatory conduction; depolarisation occurs along whole length of axon
-So nerve impulses take longer to reach neuromuscular junction; delay in muscle contraction
● Ions / depolarisation may pass / leak to other neurones
○ Causing wrong muscle fibres to contract

Question 5

Describe the nature of the refractory period

Answer 5

● Time taken to restore axon to resting potential ,no further action potential can be generated
● As Na+ channels are closed / inactive / will not open

Question 6

Explain the importance of the refractory period

Answer 6

● Ensures discrete impulses are produced (action potentials don’t overlap)

● Limits frequency of impulse transmission at a certain intensity (prevents over reaction to stimulus)
● Also ensures action potentials travel in one direction – can’t be propagated in a refractory region