Electrical Excitability - The Action Potential and its Properties Flashcards
What is an action potential?
A change in voltage across the membrane, caused by depolarisation of the membrane. It’s an all or nothing action. It travels across cells to elicit a response.
What does the action potential depend on?
Ionic gradients and the relative permeability of the membrane.
What does it mean that it needs a threshold level to be reached?
A certain potential is needed to be reached in depolarisation in order for an action potential to be caused. When this threshold is reached it can’t go back, an action potential will be reached and propagated.
How does the axon hillock relate to the threshold?
The closer depolarisation occurs to the axon hillock the more likely threshold is to be reached.
Which ion is responsible for the action potential?
The influx of sodium. This is because both the electrical gradient and the chemical gradient is towards the inside of the cell. Meaning Na+ wants to go in.
What happens during depolarisation?
Na+ wants to go into the cell as both the electrical and chemical gradients are in favour of going into the cell.
As an action potential is about to go back to the resting potential it will become slightly more negative than the resting potential before it goes back to the resting potential. Why is this?
Because voltage gated K+ channels are still open. They have not had the time to close yet.
How does the membrane repolarise?
By inactivation of Na+ channels and opening of K+ channels. This causes Na+ influx to stop and K+ efflux to begin. This gives a more negative cell interior.
What is the absolute refractory period?
When another action potential cannot happen. This is because nearly all Na+ channels are inactivated. Not just closed but inactivated.
What is the relative refractory period?
The Na+ channels recover from their inactivation and their excitability returns to normal as the Na+ channels recover from their inactivated states and the voltage-gated K+ channels close. The RRP is still hyperpolarisation but technically another action potential can happen here.
What is the structure of a voltage gated Na+ channel?
They have a pore region where the Na+ will pass through. It’s a six transmembrane protein. It has one alphasubunit which consists of 4 similar sections. It has a voltage sensor on S4 and an inactivation particle. Important to note is that it is only one alpha subunit.
What is the structure of a voltage-gated K+ channel?
Pore region. Six transmembrane protein. Consist of four alpha subunits. A functional K+ channel needs four individual alpha subunits. It also has a voltage sensing S4 region. However it has no inactivation particle.
What differs between voltage-gated K+ channels and voltage-gated Na+ channels?
K+: 4 alphasubunits and no inactivation particle
Na+: 1 alpha subunit and has an inactivation particle
Many local anaesthetics can be protonated or unprotonated. Which form is membrane permeable?
The unprotonated.
What is lidocaine used for?
Treat certain cardiac arrhythmias.
