Membrane Potentials Flashcards
What is resting memebrane potential
Electrical potential difference across the membrane. Usually -70 mv
What is an action potential and where does it stem from
A rapid change in membrane potential. The permeability or k+ and Na changes
Forms in the axon hillock
Which channel maintains the negative rmp directly
The k+ leak channel. K+ moves out of cell via diffusion down conc gradient
Why is the membrane called impermeable to NA+ and permeable to K+
Because when cell is resting k moves out of cell freely via the k leak channel
Na+ in transported back out of the cell by the Na pump (ATPase) actively when na tries to move in by diffusion (leak channel)
What 2 things cause chemical disequilibrium
The high permeability to k+ and the active transport of na + out of cell when resting
Why is the na+ pump called electro genic
Because it changes the potential difference of the outside to be more positive
What does the electrical gradient mean when talking about the k leak channel
The more k diffuse out of cell the bigger the electrical charge difference (electrical gradient)
What happens eventually when so many k+ leave the cell
They become attracted back into the cell due to the big negative charge
Why do k+ eventually stop moving via leak channel
When the electrical gradient becomes equal and opposite to the concentration gradient = k has no net movement
What is another word for when the k+ stop moving from leak channel
The equilibrium potential (Ek)
Which equation is used to calculate the equilibrium potential
Nernst equation finds the voltage of it
What is the voltage of Eion in Na and K
K = no net movement at -86mv
Na = + 60 mv (due to it moving in cell)
What generates the resting membrane potential
The equilibrium potential of the ions average out at -70mv - closest to the Ek because resting cell is permeable to K
Which 2 channels are involved in action potentials
Voltage gated K+ channel
Voltage gated na+ channel
Explain what happens when a cell is activated and it goes into slow depolarisation
Some Na+ channels open and they move in cell by diffusion
If they reach threshold of -55mv rapid depolarisation occurs
When threshold is met what happens in rapid depolarisation
All voltage gated Channels open and Na+ rush into cell through the ACTIVATION GATE
This occurs till a potential or +40/60 mv is met
Why does depolarisation eventually slow down and stop
K+ channels some open and k+ starts to leave the cell which opposes the positive charge of cell
What occurs in repolarisation
The inactivation gates on the Na+ voltage gated channels close. No more Na move in
The k+ voltage gated channels become active and k+ leaves the cell slowly bringing the charge of cell down
Why does hyperpolarisation occur after repolarisation
K+ channels are slow to shut and more k+ keep leaving the cell which means cell becomes too negative
However they do finally close
What happens after hyperpolarisation
The resting state is tried to be reinstated by the k+ leaky channels and the Na+ pump
When do activated gates actually close in voltage gated channels
They stay open all the way through Ap until the resting state is met again
What is the absolute refractory period
Membrane cannot generate another AP no matter the stimulus size
Na+ channels are inactivated
What is relative refractory period and when does it occur
Period when there can be another ap generated but stimulus needs to be bigger
Some Na channels recovered
Some k+ stay open
Happens in hyperpolarisation. This means the stimulus has to be stronger due to very negative charge
How does Ap move across the axon
In current loops
When the neighbouring Na+ channels open the previous ones go into repolarisation stage and the next is depolarised
