ACTION POTENTIALS Flashcards
How is the resting membrane potential established?
The resting potential is determined by concentration gradients of ions across the membrane and by membrane permeability to each type of ion. … Ions move down their gradients via channels, leading to a separation of charge that creates the resting potential.
How is that done? with Na+ & K+?
Na+/K+ -ATPase has a role to generate ion gradients which uses energy from ATP breaking to ADP producing a lot of energy to drive active transport across the membrane
3 Na+ out
2 K+ in
the potential of k?
-90mV
the potential of Na?
65 mV
What is the resting membrane potential?
-70mV
Do all cells have a membrane potential?
Yes all cells have a membrane potential, ionic gradients are important in all cells
Where do rapid changes occur in cells?
Rapid changed to occur in excitable cells like neurons, myocytes and pancreatic cells
What is membrane potential?
It is the voltage of the inside of the membrane relative to the outside (equilibrium)
What is hyperpolarisation?
it is when the inside of the membrane becomes more negative because of the opening of voltage-gated K+ ions (lets K+ out) the mV goes below resting potential when exposed to stimuli
What is depolarisation?
where the inside of the membrane becomes more positive due to the opening of the voltage-gated Na+ channels, it lets Na+ in, the more channels open mean more depolarisation. The mV goes higher than resting potential when exposed to stimuli
What is the threshold voltage?
The threshold voltage is -50 to -55mV
what does it mean when it’s an all or nothing process?
The generation of an action potential is all or nothing process, once this threshold is reached a full action potential must be generated
How fast is the generation of an AP?
Very fast: 1-2 milliseconds and high frequency
What is the magnitude independent on?
The magnitude is independent of the strength of the original stimulus
Summary of steps
Resting potential –> threshold is reached –> sodium channels are open (the depolarization stimulus) –> produces the action potential –> repolarisation
What are voltage-gated Na+ and K+ channels
a gate that opens when a change in voltage occurs
What occurs during the resting stage?
In the resting stage (-70mV) the ion gated sodium and potassium channels and the cell’s selective permeability are inactivated resulting in no movement
What occurs in Na+ channels
When depolarisation occurs, to let Na+ ions in. It has a three-step stage where the gate remains closed, once stimulated, the voltage-gated Na+ ion channels opens where Na+ can enter the cell. Once the stimulus strength is sufficient an action potential is produced. Once the action potential is produced the voltage-gated Na+ channels inactivate, facilitating repolarization to the resting potential. The channel’s a gate (activation gate) is closed at rest and activates in several steps to an open state after depolarization.
How does the Na+ channel become inactivated?
The peptide that sits on the end of the channel, in short time blocks the channels then it eventually closes (the tail moves) There are three processes, you cannot skip them! This Na+ process is faster!
What occurs in the voltage-gated K+ channels?
Repolarisation occurs, where the K+ channels open and K+ ions rush out of the cell, generally this process is slow. There are only two steps open and closed. The Na+ channels are inactive ans it start to close
What occurs in an action potential! LABEL
LLL
What occurs in the undershoot?
A small hyperpolarisation occurs, it needs Na+/K+ ATpase to restore Na_ and K+ concentration
What happens in absolute refractory period?
Absolute refractory period: during this time it is absolutely impossible to send another action potential. The inactivation (h) gates of the sodium channels lock shut for a time, and make it so no sodium will pass through. No sodium means no depolarization, which means no action potential. Absolute refractory periods help direct the action potential down the axon, because only channels further downstream can open and let in depolarizing ions.
What occurs in relative refractory period?
Relative refractory period: during this time, it is really hard to send an action potential. This is the period after the absolute refractory period, when the h gates are open again. However, the cell is still hyperpolarized after sending an action potential. It would take even more positive ions than usual to reach the appropriate depolarization potential than usual. This means that the initial triggering event would have to be bigger than normal in order to send more action potentials along. Relative refractory periods can help us figure how intense a stimulus is - cells in your retina will send signals faster in bright light than in dim light, because the trigger is stronger.
