Speed of the nerve impulse

Question 1

When an action potential starts does the subsequent action potentials decrease in size?

but what can differ in ?

Answer 1

No, The action potential at the end of an axon will have the same size
(or ‘electrical energy’) as the one initiated at the beginning.
—————————————–
The speed of action potentials

Question 2

What does the speed of A.P depend on?

Answer 2

properties of the axon.

Question 3

What are the factors that affect the speed of A.P?

Answer 3

1. Myelination
2. The Axon Diameter
3. Temperature

Question 4

How does Myelination affect the speed of A.P?

Answer 4

1-action potentials travel very fast in
myelinated neurones

2-The many layers of the myelin sheath result in specific parts of the
axon being electrically insulated.

3-Remember that in those areas, no action
potentials can occur.

4-This means that they have to be initiated
at the Nodes of Ranvier.

5-They then ‘jump’ from node to node.

Question 5

How does the axon diameter affect the speed of A.P?

Answer 5

1-axons with a larger
diameter conduct action potentials much quicker than their
narrower counterparts.

2-In larger axons, the positive ions tend
not to ‘leak’ as much as in narrow
axons

3-This means that membrane potentials
are more easily maintained.

4-This speeds up action potentials

Question 6

How does the temperature affect the speed of A.P?

Answer 6

1-Higher temperatures will therefore increase the rate of diffusion of
IONS

2-The energy required to drive the sodium-potassium
pumps (used to restore resting potential) is generated in
respiration.

3-Higher temperatures increase the efficiency of enzymes involved in
respiration

Question 7

What is the refractory period?

can any further action potentials can be generated?

Answer 7

the time that it takes for
sodium influx to be possible
again.
—————————
No

Question 8

What are the purposes of the refractory periods?

Answer 8

1. Ensuring That Action Potentials Are Only Propagated In One Direction:

• When an action potential occurs in one area of an axon, we know
  that it stimulates the area next to it to initiate the next action
  potential…
• It can only do this if the next area is at resting potential.
• The area before the action potential will be in the refractory period, so
  a new action potential could never be generated here.

2. Refractory Period Ensures That Action Potentials Are Discrete (Separate):

• This reason is related to the previous one.
• Due to the refractory period, a new action potential cannot be
  formed immediately behind the first one.
• ## This ensures that action potentials are separated from each other.
  3. Refractory Period Limits The Number Of Action Potentials
     Passing Along An Axon At One Time:
• Use your brain on this one.
• Axons are only so long.
• If the refractory period controls which way action potentials travel
  in, and also produces discrete action potentials…
• … then only a certain number of action potentials will ‘fit’ on an
  axon!

Question 9

What is the all-or-nothing principle?

Answer 9

1. If a stimulus does not have enough energy, it will not reach the threshold value
2. Basically, a weak stimulus will not cause enough sodium ions to enter the axon, meaning the voltage does not reach the threshold
3. Stimuli that do reach the threshold, all-cause action potentials of the same strength. It does not matter how much above the threshold
   -the action potential will always be the same