Lecture 8: Action Potential Flashcards
How can Membrane potential can be visualised in real-time?
with an oscilloscope or specialised software
what are the 5 phases of action potential ?
- Resting:The membrane is at the RMP (–65 mV).
- Rising phase: a rapid depolarisation of Vm.
- Overshoot: inside of the neuron is now positive relative to the outside.
- Falling phase: rapid repolarisation 1 of Vm.
- Undershoot: inside of the neuron is now more negative than at rest (hyperpolarised).
whats it called when membrane potential increases, positive to rest?
depolarisation
whats it called when membrane potential decreases?
repolarisation
what will the Injection of positive current into a neuron do?
depolarise the membrane potential
The _______ the stimulus, the _____ action potential a neurone will generate
- stronger
2. more
The magnitude of each action potential is the ____.
same
what does tonic firing in stellate neurones look like?
spikes are very close together
what does Spike adaptation is medium pyrimidal neurons look like?
spikes are further apart
Some neurons can be toggled into more than one firing mode depending on their _____ _____.
membrane potential
Na+/K+ pumps maintain what?
concentration gradients across the membrane
Astrocytes buffer extracellular ______ concentrations.
potassium
what’s needed for a functioning nervous system?
Negative charge inside of a neurone is a requirement for a functioning nervous system.
what are the two states of a neuron?
action and resting
what are the conditions at rest?
there is a large concentration and electrostatic push on sodium to enter a neuron
what happens at an action potential?
- Na+ rushing into the neurone makes the inside more positive than normal.
- The membrane becomes permeable to Na+, diffusion and electrostatic pressure push Na+ into the neurone.
- for an instant membrane eis more permeable to Na+.
The _____ _______ must cross the ______ in order for a neuron to have a action potentials.
membrane potential
threshold
at the threshold what is the membrane more permeable towards?
sodium
Are voltage-gated channels sensitive to changes in membrane potential?
yes
what happens at threshold, linked to activation of bolted gated Na+ channels ?
interior of the cell is positive enough to repel the positively-charged voltage sensor of the Na+ channel. Allowing Na+ through the pore.
what holds the Na+ channels closed?
Negative interior attracts positive charge of voltage sensor and holds channel closed. More positive interior repels voltage sensor thereby opening the channel.
what happens when sodium channels pop open for a short time?
- Depolarisation to Threshold opens Na+ channels.
- Na+ channels inactivate a short time later (<1 msec).
- A globular (glob) portion of the channel blocks the open pore.
- Channels remain inactivated until repolarisation to rest.
what does depolarisation of a neurone lead too?
Depolarising a neuron leads to Na+ channel activation which leads to further depolarisation and the opening of more Na+ channels!
An action potential is initiated at the _____ _____.
axon hillock
where are some Na+ channels located?
from the hillock down the entire length of the axon
what do Dendrites do?
Dendrites receive signals from other neurons.
what happens in the rising phase?
- The positive interior repels the voltage sensor thereby opening the channel
- Voltage-gated Na+ channels open at Threshold.
- Opening of voltage-gated Na+ channels; Vm depolarises.
- Inactivation of Na+ channels.
what happens in the falling phase?
- K+ flows out of the neurone down both its concentration and voltage gradients.
Voltage-gated K+ channels are known as what, and why?
Voltage-gated K+ channels are known as delayed rectifiers since they open about 1 ms after Na+ channels.
Voltage-gated K+ channels _______ at _______, too, but they take ______ to open
activate
threshold
longer
Are K+ channels involved in action potential the same as those that mediate RMP?
no they are not the same
During the undershoot, the permeability of the membrane to K+ is what?
and this causes what?
higher than it is at rest causing the Vm to reach EK.
what does the refractory periods do the regeneration of an action potential?
makes it difficult or impossible.
what is the Absolute Refractory Period?
when Na+ channels are still inactivated therefore making it IMPOSSIBLE to generate another action potential.
what is the Relative Refractory Period?
Na+ channels have de- inactivated and it takes more positive current to bring the neuron to ring threshold
what happens to channels at rest?
At rest, both voltage-gated Na+ and voltage-gated K+ channels are closed.
what is the permeability of the membrane like at rest?
The permeability of the membrane for Na+ is low, but high for K+ since background K+ channels are open helping to maintain the RMP.
what happens at the rising phase of the action potential?
- If the neuron is depolarised to Threshold then both voltage-gated Na+ and voltage- gated K+ channels are activated.
- Increased positive charge in the neuron repels the voltage sensors on both voltage-gated Na+ and K+ channels.
- Voltage-gated Na+ channels pop open and Na+ immediately flows into the neurone bringing Vm close to ENa (~ +40 mV) in <1 ms.
- K+ channels slowly start to open.
what happens at the overshoot phase ?
- Voltage-gated Na+ channels inactivate before Vm reaches ENa due to the pore becoming blocked from the inside.
- In less than 1 ms the Vm nearly reaches ENa, but voltage-gated Na+ channels inactivate. K+ channels have yet to fully open.
- Na+ channels are still open, but they are inactivated due to the block by the globular portion of the channel. Voltage- gated K+ channels are still slowly opening.
wha happens at the falling phase of the action potential?
- Voltage-Gated K+ channels open and K+ leaves the neuron and repolarises Vm to a more negative value.
- During repolarisation, Na+ channels are open, but inactivated, and K+ is pushed out of the neuron down its concentration and voltage gradients.
- The high concentration of K+ inside of the neuron together with the fact that the Vm is close to ENa forces K+ out through the now fully-open voltage-gated K+ channels.
what happens at the The absolute refractory period?
- Na+ channels close, but K+ channels stay open which hyperpolarises the membrane to EK (–80 mV).
- The increased membrane permeability to K+ allows it to continue flowing down its concentration gradient out of the neuron bringing Vm to EK.
- Na+ channels, are inactivated thereby preventing the initiation of another action potential.
what happens at the relative refractory period?
- Na+ channels finally de-inactivate and K+ channels have yet to fully close. The membrane is still hyperpolarised.
- It takes much less positive current to bring the neuron to ring Threshold when Vm is at rest at –65 mV as opposed to when it is hyperpolarised to –80 mV
- It is now possible to generate another action potential, but it takes significantly more positive current to bring the neuron to Threshold.
what does Lidocane do?
This chemical inhibits action potentials by binding to and preventing Na channels from opening.
