Pharmacology- The Action Potential Flashcards
Depolarisation
the membrane potential becomes less negative or even positive
Hyperpolarisation
the membrane potential becomes more negative
Direction of change in potential depends on
- direction of movement of the ion (influx or efflux)
- charge carried by the ion
what drives passive movement of an ion through an ion channel?
electrochemical gradient for the ion
what direction does Na+ flow and why?
Vm-Ena
= -70 - 60
=-130-> negative-> inward movement
what direction does K+ flow and why?
Vm-Ek
=-70 - (-100)
=30-> positive-> outwards movement
Ion channel
protein complex which spans the lipid bilayer forming a central pathway which permits the rapid flow of selected ions
Describe the activation of Na+ channels
Self-reinforcing- the opening of a few channels causes a few more to open, causing further depolarisation and so on
this is positive feedback
Describe the activation of K+ channels
self limiting
outward movement of K+ causes repolarisation, which turns off the opening stimulus
this is negative feedback
Absolute refractory period
no stimulus can elicit a second action potential ie all Na+ channel are inactivated
Relative refractory periof
a stronger than normal stimulus can elicit a second action potential (membrane is hyper polarised, mix of closed and inactive channels)
Why do passive signals not travel far from their origin site in nerve cells
current is lost across membrane and there is a reduced change in potential
How to increase passive current spread and therefore action potential velocity
- increase axon diameter, thus increasing current spread
- decrease leak of current across the axon by myelinating the axon
What mediates the upstroke/ depolarising phase?
opening of voltage activated Na+ channels
What causes the downstroke?
opening of voltage activated K+ channels and inactivation of Na+ channels
