The Action Potential Flashcards
1
Q
Characteristics Of Action Potentials
A
- All-or-none law
* voltage gates at the trigger zone always open if threshold is reached - Nondecremental
* does not get weaker with distance 3. Irreversible
* once started goes to completion and cannot be stopped
2
Q
Action Potential
A
- The mechanism by which neurons conduct electrical signals.
- An “all or none response”
- Action potentials depend on several types of ion channels that regulate Na + and K + permeability (PNA and PK)
- Brief change in voltage caused by movement in ions.
- Results in change in membrane potential.
- Ions are self-serving and function to reach their equilibrium potential (if given the chance)
- K+ (hyperpolarization)
- Na+ (depolarization)
3
Q
Depolarization – Positive Feedback Drive Transmission Of The Signal
A
- Threshold potential is reached at the axon hillock
- The axon is enriched in voltage-gated Na+ channels
- Local voltage-gated Na+ channels open causing further depolarization
- The Hodgkin cycle
4
Q
Graded Potentials
A
- Short distance signals and travel via electronic current spread
- Graded potentials are caused by ligand-gated Na+ channels
- The concentration of + ions (Na+) is highest near the channel
- Local depolarization
- Depolarization moves through a cell via positive and negative ion interaction.
- New Na+ ions are drawn toward (-) ions and away from (+) ions
- spread of depolarization like ripples in a pond.
5
Q
Signal Integration
A
- Axon hillock “decides” if an action potential will occur.
- Depends on strength of graded potentials.
- Axon hillock aka Trigger Zone - contains many voltage gate Na+ channels.
6
Q
Threshold Potential
A
- The depolarization level required to initiate an action potential.
- Generally -55mV in neurons
7
Q
Subthreshold
A
- less than +15 mV; a graded potential not large enough to trigger an action potential.
8
Q
Suprathreshold
A
- Graded potential that is larger than needed to trigger A.P.
9
Q
Spatial Summation
A
- Graded potentials at two locations influence the net changes in membrane potential at the axon hillock
10
Q
Temporal Summation
A
- Graded potentials at two overlapping times influence the net changes in membrane potential at the axon hillock
11
Q
Signal Reception
A
- Sum of graded potentials from local depolarization of dendrites and soma.
12
Q
Signal Integration
A
- Axon hillock contains voltage-gated Na+ ion channels
- Open at -55 mV, triggering an action potential
13
Q
Steps To Trigger An Action Potential In A Neuron
A
- Graded potentials move to axon hillock
- If threshold is reached, depolarization occurs via activation of voltage-
gated Na+ channels - Repolarization by inactivation of voltage-gated Na+ channels and activation of voltage-gated K+ channels
- Hyperpolarization caused by voltage-gated K+ channels staying open longer
than needed to reach RMP. - Return to normal permeability by closing of voltage-gated K+ channels and the Na+/K+ pump
14
Q
Conduction Of An Action Potential
A
- Similar to knocking over a row of dominoes
- All or nothing response
- An A.P. never stops halfway down an axon
Electrotonic current flow causes local depolarization
An action potential in one area triggers action potentials in another
Therefore, conduction of an action potential down the axon represents a combination of action potentials at specific points on the axon.
Dependent on the voltage gated Na+ ion channels.
15
Q
Myelinated Regions Of Axons: Internodes
A
- Lipid-rich cells insulate some neurons
- Schwann cells are in the PNS around motor neurons
- Wrap around the axon several times.
