1
Q
6 properties of action potential
A
- triggered by depolarisation
- threshold of depolarisation
- all or none
- propagates without decrement
- at peak: Vm approaches E(Na)
- refractory period - in-excitable
2
Q
describe structure of K channels
A
2 or 4 subunits
3
Q
what happens when membrane becomes permeable
A
during AP membrane e becomes permeable to Na first the K
E(Na) –> E(K)
4
Q
what does prolonged depolarisation cause
A
sodium inactivation
5
Q
why is there a threshold
A
at rest P(K)»_space; (P(Na)
flow of K out counteracts flow or Na in
6
Q
eqn. for charge
A
charge = capacitance x voltage
Q (coulombs)= C x V
7
Q
what can a transmembrane current be (2)
A
resistive - ions flow through channel
capacitative - ion approaches one surface of membrane, another is expelled from other side
8
Q
describe myelinated conduction
A
- as axon diameter increases, R(L) decreases
- increase R(M)=current forced through axoplasm to next node
- decreased C(M) - charge not stored at membrane
9
Q
describe unmyelinated conduction
A
- thinner axons: higher longitudinal axoplasmic resistance
- lower R(M) (membrane resistance)- current dissipates faster, voltage falls rapidly
- higher C(M)- voyage changes more slowly
