action potentials

Question 1

6 properties of action potential

Answer 1

1. triggered by depolarisation
2. threshold of depolarisation
3. all or none
4. propagates without decrement
5. at peak: Vm approaches E(Na)
6. refractory period - in-excitable

Question 2

describe structure of K channels

Answer 2

2 or 4 subunits

Question 3

what happens when membrane becomes permeable

Answer 3

during AP membrane e becomes permeable to Na first the K

E(Na) –> E(K)

Question 4

what does prolonged depolarisation cause

Answer 4

sodium inactivation

Question 5

why is there a threshold

Answer 5

at rest P(K)&raquo_space; (P(Na)

flow of K out counteracts flow or Na in

Question 6

eqn. for charge

Answer 6

charge = capacitance x voltage

Q (coulombs)= C x V

Question 7

what can a transmembrane current be (2)

Answer 7

resistive - ions flow through channel

capacitative - ion approaches one surface of membrane, another is expelled from other side

Question 8

describe myelinated conduction

Answer 8

• 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

Question 9

describe unmyelinated conduction

Answer 9

• thinner axons: higher longitudinal axoplasmic resistance
• lower R(M) (membrane resistance)- current dissipates faster, voltage falls rapidly
• higher C(M)- voyage changes more slowly