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
