L2 - Spikes

Question 1

How do spikes travel?

Answer 1

Propagation, saltory conduction - jumps from node to node - neurons are poor conductors

Question 2

What 3 ways increase conduction in neurons?

Answer 2

1) Myelination - glial cells (lipid)
2) Axon width - wider is faster
3) Temperature - hotter is faster

Speed is <1m/s (up to 100m/s)

Question 3

Describe how different pumps and channels maintain the resting potential

Answer 3

1) Na/K ATPases pump - Na+ out of the dell and K+ into the creating a high internal K+ concentration
2) K+ channels - allow K+ to diffuse over the membrane,, which they tend to do out of the ell due to the gradient created by the Na/K+ ATPases
3) Electrical gradient - K+ diffusing out is removing positive charge from inside the ell and putting it on the outside, therefore making the inside of the cell more negative than the outside
4) K+ equilibrium

Question 4

Describe what is meant by the K+ equilibrium

Answer 4

The negative charge created inside the cell by the Na/K ATPase (3+ out 2+ in each time) pulls K+ back inside the cell.
At the same time the concentration gradient created makes it diffuse back out

K+ reaches an equilibrium between concentration and electrical gradient = the K+ equilibrium potential (around -96mV)

Question 5

Describe the creation of an action potential

Answer 5

1) a few VG-Na+ channels open, causing an influx of Na+
2) Some Na+ channels opening causes Na+ to rush down the gradient into the axon, depolarising the membrane even more - a positive feedback mechanism
3) At the peak AP, Na+ channels become inactive and K+ channels open and K+ begins to leave the cell.

Question 6

What is hyperpolarisation and the refractory period? How are they reversed?

Answer 6

The membrane becomes hyperpolarised as K+ continues to leave the cell, the hyperpolarised cell is in a refractory period and cannot fire again.

The K+ channels close and the Na/K ATPase restores the resting potential