Nerve Cell Potentials Flashcards
What is the Nernst equation?
Ex= (RT/zF).loge([K+ outside]/[K+ inside])
R=gas constant T=absolute temp z=charge of ion and F=Faraday constant
What is the Nernst equation used for?
To measure the equilibrium potential
Why is the RMP never as large as the equilibrium potential?
As some Na+ can get through too which means K+ never reaches equilibrium
How do ligand-gated channels work?
- Open and close in response to binding of ligands
- This causes release of the neurotransmitter into the synaptic cleft
- After binding, the channel changes shape and opens up
Where are ligand-gated channels found?
On post-synaptic membranes
What reverses the change in shape of the ligand-gated channel?
The removal of the neurotransmitter
What does the shape and size of an action potential depend on?
The synaptic event
What is an electrotonic potential?
Where Na+ is allowed in at a specific location causing that section of the membrane to depolarise. Current flows from a more positive to a less positive charge and so the depolarisation spreads
However the signal is only carried for a short distance
What triggers an action potential?
Many electrotonic potentials
What is the main difference between action potentials and electrotonic potentials?
Electrotonic potentials are fired whenever Na+ is allowed into the cell
Action potentials are fired only when the diffusion of Na+ into the cell causes the potential difference to reach the threshold
What is the role of voltage-gated Na+ channels in depolarisation?
- they open and close in response to changes in voltage
- closed at rest
- have a positive charge attached to it which is attracted more to the inside (as inside is more negative)= closed gate
- electrotonic potentials eventually cause depolarisation
- force holding the gate closed is weakened= opens
- positive charge on gate now attracted to the outside (as outside is now more negative)= doesn’t close
How is the influx of Na+ stopped?
The inactivation gate, which also has a positive charge attached to it, is pulled towards the outside and therefore shuts close
What ensures that the action potential is all-or-nothing?
Positive feedback which causes the rapis activation of all available channels
How do anaesthetics effect action potentials and so what must be ensured when giving anaesthetics?
Interferes with voltage-gated Na+ channels, abolishing action potentials
Must make sure that anaesthetics don’t get into the bloodstream
Give examples of anaesthetics that effect action potentials
Lidocaine
Neurotoxins such as tetrodotoxin and funnel-web spider toxin
What is the refractory period?
The period where action potentials can’t be fired again
What does the refractory period ensure?
That there’s no overlap or too rapid firing of action potentials until the membrane is back to its RMP
