Lecture 27 Flashcards
If the potential inside neurons becomes more negative:
The potential inside the cell moves closer to Ek+ and away from ENa+
If the potential inside the cell becomes less negative:
The potential moves closer to ENa+ and away from Ek+
Hyperpolarisation:
The potential becomes more negative
Depolarisation:
The potential becomes less negative
The action potential is:
A brief fluctuation in membrane potential caused by a transient opening of a voltage-gated ion channels, which spreads like a wave along an axon.
Action potentials occur when:
The membrane potential reaches certain voltage called the threshold (~55mV)
Three stages of action potential:
- Fast depolarisation (to about +30mV, or ‘overshoot)
- Repolarisation:
- After-hyperpolarisation
Which stages of action potential are absolute refractory periods?
1 and 2 (fast depolarisation and repolarisation)
Which stages of AP are relative refractory periods?
3 (After hyperpolarisation)
What happens when MP reaches the threshold?
There is a sudden activation of voltage gated Na+ channels.
P Na+ increases.
Therefore MP shifts towards the ENa+ –> overshoot
Repolarisation:
Fast depolarisation is followed by the transient opening of voltage gated K+ channels, leading to repolarisation and AHP.
MP shifts towards Ek+ since Pk+/PNa+ becomes 100: 1.
Influx of Na+ slows down and stops when:
- The inside potential becomes potential (moves towards ENa+) and thus attracts Na+ ions less.
- Na+ channels inactivate.
How can AP be evoked?
Anode
Cathode
Current flows from:
Outside from + to -
or Across membrane and inside axon
When the current generated by an outside source flows through the cell membrane from outside to inside
hyperpolarisation
