Action Potentials Flashcards
What is the pattern of communication in the nervous system?
Sensory stimulus -> neural code -> Interpretation/Action
How long can action potentials travel?
0.1mm to 1m
What are the 4 phases of an action potential?
- Rising Phase (depolarization)
- Overshoot
- Falling phase (repolarization)
- Hyperpolarization
What is the difference between an absolute and relative refractory period?
An absolute refractory period means no other action potentials can be fired at this time, a relative one means that it is just much more difficult to fire an action potential
Who was responsible for the discovery of in squid?
Hodgkin + Huxley
What can we say mathematically about different ion channels at rest?
Gk «< Gna
What happens to channels when depolarization happens?
Rapid opening of Na channels
What happens to channels during the repolarization phase?
The rapid closing of Na channels and slow opening of K channels
What did Hodgkin and Huxley conclude about action potentials?
It requires that certain channels become inactivated independent of membrane potential.
What is the variable of interest in a voltage-clamp experiment?
Current
How can we verbalize the results of a current clamp experiment?
How can we measure Vm by injecting currents through an electrode?
How can we verbalize the results of a voltage clamp experiment?
To measure Im at a desired Vm, we fix Vm at a value and determine the current needed to keep Vm equal to Vclamp
What can we learn about the neuron based on the voltage-clamp experiments?
We can measure the Na+ and K+ currents activated when Vm is at different points in an action potential cycle
What ionic current is activated by the depolarization and is sustained throughout the depolarization?
The K+ current
What happens to the Na+ current when a depolarization happens?
The current is activated by a depolarization but is not sustained - it deactivates itself
What is patch clamping?
It is a way of determining the permeability of a single channel of a cell membrane. It involves extracting a portion of membrane and imposing a voltage on it
What are the three types of patch clamping?
- Cell attached
- Inside-Out mode
- Whole-cell mode
How can we tell if a channel is voltage gated?
When the voltage across the membrane is higher or lower with the same ion concentration, the frequency of action potentials change.
What are the two gates that are responsible for the status of channels?
The activation and inactivation gate
What is the gate cycle of channel cells?
Closed (activation gate closed, inactivation gate open)->
Open (activation gate open, inactivation gate open) ->
Inactivated (activation gate open, inactivation gate closed)
What gate cycle phases are associated with which neuronal action potential cycle phases?
Activation = Polarization
Inactivation = maintained depolarization
Recovery from inactivation = repolarization
Would a voltage gated cell be more likely to be open at -80 or -40mv?
-40
What can be said about delay times and how long Na+ channels remain open?
They open very rapidly and remain open for about 1 ms
What is the mechanism responsible for the quick closure of Na+ channels?
The ball and chain mechanism
