2 - Membrane Excitation

Question 1

intra/ex ion concentrations?

Answer 1

na/ca higher outside

k higher inside

Question 2

what is the normal membrane potential?

Answer 2

-65mv
membrane is negative at rest
Em is membrane potential

in neruones Em is around -70

Question 3

what 2 types of channels control ion conc?

Answer 3

1. permanent
   - NA/K/CA channels always open
2. gated
   - leak channels/voltage gated/ligand gated
   leak set Em
   voltage control action pot

Question 4

how do chemical and electrical force influence ion movement?

Answer 4

Chemical Grad

• if unequal ion distribution
• so K moves out [efflux]
• Na moves in [influx]

Question 5

how is a membrane potential [-65mv] set? assumptions included first

Answer 5

assume start at 0 mv
assume permeable to only K or Na

1. chemical gradient causes K efflux so inside becomes more -
2. • mv causes Electrical force
3. K influx caused as it attracts + to - inside
4. but efflux is higher than influx
5. till chem and elec are balanced
   no more K movement

so Em is a in between of eq potential of K and Na

Question 6

what is equilib potential?

Answer 6

• when the ions chemical and electrical force is equal

Question 7

eq pot for Na and K?

Answer 7

K has eq pot of -80mv
Na has eq pot of +60

Em rests in between both [-65]

Question 8

what is occurring at -65mv in terms of Na and K movement?

Answer 8

neither K or Na satisfied about not being at their value

so driving force occurs

• Na influx [to get to +60] caused by elec and chem grad
• K efflux [get to -80mv] caused by chemical [but also K influx due to electrical gradient]

so K EFFLUX IS EQUAL TO NA INFLUX [due to leak channels