L4 Flashcards
For cell to be excitable:
- Receive and respond to stimuli
- Have a resting membrane potential - i.e. Difference in voltage across membrane
- Be able to rapidly change this membrane potential- i.e. ACTION POTENTIALS
Bioelectricity
Created by ions moving across membranes
Movement of ions is affected by:
Chemical force
Electrical force
Chemical and Electric forces are OPPOSING
How do ions pass through cell membrane
Ion channels only
- leaky IC:
- Ligand gated IC
Features of ion channels
- V selective - only all Na ions to pass for ex.
- Aqueous pores in membrane
- Leaky - open all, the time
- Gated - specific factors open them e.g. Depolarisation of membrane potential. Or ligand binding
- Down CG
Why cell is + outside and - inside
- Because pos+ K+ molecules follow their CG and move out of cell
- Thus inside becomes neg-
Reversal potential
- When electrical and chemical driving force are equal
- Therefore, the net flux (no ATP necessary) of ions is nil
- The equilibrium potential = reversal potential
- Represents the max potential the membrane would reach if it was only permeable to one ion only eg Na.
Na: +60mV
K : -95mV
Flux is Na and K will bring the membrane potential to what value hypothetically
This would only happen if membrane was permeable to one ion only
Na: +60.5
K: -95
What provides the energy for ions to move down conc gradient
Na+/K+ ATPase pump
NB NB NB NB
What does the Na ATPase pump do
- 3 Na+ out
2 K+ in - Active ion transporter - depend on ATP
Ate they moving against their conc grad tho???i yes
- Mildly electrogenic (causes small change in membrane potential) but only v small contribution
Why is RMP of K+ not equal to reversal potential?
K+ channels are not always open
As well as K+ currents- there are Na and Ca currents which depolarise membrane - make it more positive ( they travel into the cell down their CG)
