action potentials Flashcards
when cell membrane of neurones are stimulated do they become polarised/depolarised
DEPOLARISED
Action potentials: sequence of events
1) Stimulus
2) Depolarisation
3) Repolarisation
4) Hyperpolarisation
5) Resting potential
The bigger the stimulus…
the faster a change in potential difference occurs
Action potential: Stimulus
The stimulus excites the membrane of the neurone, which causes sodium ion channels to open and the membrane becomes more permeable to sodium.
Sodium ions diffuse down the sodium ion electrochemical gradient , this makes the inside of the neurone LESS NEGATIVE
Action potential: Depolarisation
If potential difference reaches the threshold (-55mV) then voltage gated sodium ion channels open, and more sodium ions diffuse into the neurone.
Action potential: Repolarisation
At around 30mv sodium ion channels close and voltage gated potassium ion channels open.
membrane becomes more permeable to potassium ions, so potassium ions diffuse out of the neurone down the potassium ion concentration gradient.
This starts to get the potential difference of the membrane back to resting potential
Action potential: Hyperpolarisation
The potassium ion channels are “slow to close”, which means there is a slight “overshoot” where too many potassium ions are diffusing out of the neurone, which causes potential difference to become more negative than resting potential (-70)
Action potential: Resting potential
The ion channels are reset
sodium potassium pump returns membrane to its resting potential.
what is the refractory period
The period of recovery after an action potential has been fired
( can not be fired straight away due to closing of channels)
bigger stimulus allows action potentials to be fired…
more frequently
Once the threshold is reached what happens?
Action potential fires with the SAME CHANGE IN VOLTAGE ALWAYS
no matter how big the stimulus
if threshold isn’t reached
then action potential WONT FIRE
what is a myelinated neurone
A neurone with a myelin sheath
- a myelin sheath is an electrical isulator
what cells are myelin sheath made up from
Schwann cells
where does depolarisation occur in a mylinated neurone
In the nodes of ranvir
- sodium ion channels are concentrated at the nodes
