Nerve impulses: transmission 5.3.5

Question 1

How is the impulse passed along the axon?

Answer 1

When a neurone is stimulated, the action potential does not actually travel along the axon, but instead triggers a sequence of action potential along the axon.
- Due to the insulation of the myelin sheath
( the refractory period allows it to travel in only one direction )

Question 2

What is the all or nothing rule?

Answer 2

States that the action potential only occurs if the stimulus causes enough sodium ions to enter the cell, to change the membrane potential to a certain threshold level.

If the depolarisation is not great enough to reach the threshold, then the action potential (and hence an impulse) will not be produced.

Question 3

What is a generator potential?

Answer 3

It occurs when a few channels open, and they allow a few sodium ions into the cell a produce a small action potential.

Question 4

What does an action potential cause in the neurone?

Answer 4

• Depolarisation of that section of the axon.
• The current causes the opening of sodium ion channels a little further up th axon.
• This causes an influx of sodium ions in this section, resulting in an action potential in this direction.
• The previous section is in the depolarisation stage and is unresponsive.
• This makes the action potentials discrete events and means the impulses can only travel in one direction (refractory period).

Question 5

What happens when the strength of stimulus increases?

Answer 5

The receptor potential increases - generating a high frequency (not amplitude) of impulses in the sensory neurone

Question 6

Where does depolarisation occur in myelinated neurones?

Answer 6

At the nodes of Ranvier, only in one direction as repolarisation is occurring at the previous node