Action Potentials Flashcards
How long from start to finish is an action potential?
The process of an AP firing from start to finish is approximately 3ms with the peak at about 1ms!
what does resting membrane potential mean?
differences in concentration of ions – outside more positively charged
explain the features of resting membrane potential
- Poised and ready to fire (measured as an electrical potential).
- Electrical and chemical force at the same time:
o Electrical force: opposites attract – outside more positive.
o Chemical force: concentration gradient – unequal ion concentration. - Requires lots of energy (concentration gradient maintenance).
o Na+/K+ exchanger
3 Na+ out/2 K+ in
Uses a lot of ATP - -70mV resting potential
what are the 2 forces during resting membrane potential?
electrical and chemical
electrical force at resting membrane potential
opposites attract – outside more positive.
chemical force at resting membrane potential
concentration gradient – unequal ion concentration.
how much energy does resting membrane potential require?
a lot!
what is the o Na+/K+ exchanger?
3 Na+ out/2 K+ in
Uses a lot of ATP
what is the figure for resting potential?
- -70mV resting potential
Explain the process happening at resting membrane stage of AP if an excitatory NT is released
The NT attaches to the ligand-gated Na+ channel which opens the channel allowing Na+ to move down the concentration gradient.
explain what happens at the threshold stage of an AP
Intracellular becomes more positive
-55mV threshold met.
The threshold opens the voltage-gated Na+ channels in the axon hillock.
threshold figure
-55mV
what are A-?
big organic ions
what ions are more highly concentrated inside the neuron at rest?
K+
A-
what ions are more highly concentrated outside the neuron at rest?
Na+
Ca2+
Cl-
what happens at the peak of an AP?
- voltage-gated Na+ channels close
- Voltage-gated K+ channels open (K+ leaves neuron) (falling phase)
- Voltage-gated K+ channels are also triggered by a change in the membrane potential but open with a 1ms delay allowing the electrical signal to generate and the AP to remain local (falling phase).
why is there a delay before the K+ channels open?
open with a 1ms delay allowing the electrical signal to generate and the AP to remain local.
what happens during the refractory period?
- (after hyperpolarisation phase – neuron overcompensates)
- -90mV before this
- Can’t fire another AP (as below resting potential)
- Na+/K+ exchanger gets to work to restore the resting state.
figure of the refractory period
-90mV
what happens in the falling phase?
- Voltage-gated K+ channels open (K+ leaves neuron) (falling phase)
- Voltage-gated K+ channels are also triggered by a change in the membrane potential but open with a 1ms delay allowing the electrical signal to generate and the AP to remain local.
how does AP transfer from neuron to neuron?
Voltage-gated calcium channels allow the transfer of AP (turn electrical signal into chemical signal – NT)
- Voltage-gated Ca2+ channels open
- Ca2+ enters
- NT move out of the presynaptic cell into the synapse and bind to the postsynaptic terminal.
what is the all or nothing principle?
AP will either fire or it won’t (no varying strengths of AP.
describe the action of inhibitory NT
- Internal becomes more negative
- Hyperpolarisation occurs (-85mV)
- So much more Na+ is needed to reach the threshold
(ligand-gated Cl- channels are located on the dendrites).
where are ligand-gated Cl- channels located?
on the dendrites
