Action Potential Flashcards
label the structures of the neuron
ion permeability in cells
Sodium - leaks a little into cell
Chlorine - doesn’t leak
Potassium has a big amount of leakage out of the cell
if the membrane permeability changes allowing more Na+ ions to enter the cell will the RMP become more or less negative
less negative
if the membrane permeability changes allowing more Cl- ions to enter the cell, will the RMP become more or less negative
more negative
mechanically gated ion channels
deforming the membrane opens the channel
ex) touch
chemically gated ion channel
a chemical binding the channel (ligand)
voltage gated ion channels
voltage changes in the cell to open the channel
label the following diagram and indicate what electrical events are important in each zone
input zone: graded potential
trigger zone: action threshold (depends on if threshold value is reached)
conducting zone: action potential (travels here)
output zone: passes signal to next neuron by releasing neurotransmitters
depolarization
cell becomes more positive than RMP
repolarization
cell returns to the RMP
threshold
the minimum voltage that will initiate an action potential
hyperpolarization
a membrane potential that is more negative than the RMP
What causes hyperpolarization?
the voltage gated potassium channels are slow to close which allow excess potassium ions to diffuse out the cell to make the cell membrane potential
graded potential
- occurs in dendrites and soma
- mechanically gated and chemically gated
- signal strength decreases
- amplitude is directly proportional to stimulus strength
- result is a action potential
- temporary changes in membrane voltage
graded potentials do not travel all the way down the axon like action potentials do. Instead, they travel only a short distance and the signal loses strength over time. Why?
the graded potential returns loses strength because the cell’s electric graded potential returns to equilibrium (decay) from ion leak channels
action potential
at the axon hillock of the neuron, if the depolarizing stimulus reaches threshold (-55 mV), an action potential will be triggered and will go down the axon (Na+ voltage-gated channels open)
- “all or none”
- require sufficient depolarization to reach reach threshold
- are the result of opening voltage gated ion channels
- are the same amplitude and duration in a given neuron
- only travel in one direction down an axon
- will trigger the release of neurotransmitters to pass the signal onto another cell or neuron
label and explain each step in the action potential
1-3: Depolarization due to graded potential (Na+ in via mechanically or chemically gated channels opening) to threshold
4: Triggers opening of Na+ voltage-gated channels—Na+ enters (depol.)
5: Na+ voltage-gated channels quick to close—Na+ stops entering (activation gate is open, inactivation gate is closed)
K+ voltage-gated channels slower to open—K+ starts leaving neuron
6: K+ leaving causes repolarization back to RMP
7: K+ voltage-gated channels slow to close so K+ continues to leave (hyperpolarization)
8-9: K+ voltage-gated channels close and returns to RMP
voltage-gated sodium channel
has 2 gates, activation and inactivation gate
when do voltage gated sodium channels open?
around -55 mV the voltage-gated sodium channels open creating a large influx of sodium into the cell
why does the sodium gated channel in action potentials have 2 gates?
the inactivation gate closes and opens much faster than the activation gate, allowing sodium to quickly enter and leave
absolute refractory period
during depolarization the sodium voltage gated channels are already opened and so can’t be stimulated to create another action potential
relative refractory period
during hyperpolarization when the activation gate is closed and inactivation gate is closed
there can be an action potential, but it would take a greater stimulus than usual to activate it as the cell is more negative than RMP
what happens to the gates during depolarization?
cell becomes more positive than RMP
potassium gate is closed
sodium activation and inactivation gate are open
what happens to the gates during repolarization?
cell returns to the RMP
potassium gates are open
sodium activation gate is open
inactivation gate is closed
what happens to the gates during hyperpolarization?
a membrane potential that is more negative than the RMP
potassium gates are open
sodium activation gate is closed
inactivation gate is open
Na+ Voltage-Gated Channel: depolarization (at threshold)
activation gate: open
inactivation gate: open
Na+ Voltage-Gated Channel: Structure at -70 mV (RMP)
activation gate: closed
inactivation gate: open
Na+ Voltage-Gated Channel: repolarization
at peak of action potential, inactivation gate closes to stop Na+ from entering
activation gate: open
inactivation gate: closed
inactivation gate re-opens and activation gate closes at RMP (remaining throughout hyperpolarization)
voltage-gated potassium channel
K+ voltage-gated channel is much slower to open than the Na+ voltage-gated channel
so we dont see the effects until a little later in the action potential
K+ leaving causes repolarization and the hyperpolarization of the action potential
has a single gate (activation gate)
leak channels
always opened channels
channel-mediated diffusion
