Action Potentials Flashcards
What does depolarization mean?
The membrane potential becomes less negative (or even positive)
What does hyperpolarization mean?
The membrane potential becomes more negative.
what two factors effect the change in membrane potential (depolarization or hyperpolarization)?
- the direction of the movement of ions
- the charge carried by the ion.
What two components make the electrochemical gradient?
Concentration gradient + chemical charge gradient
What direction of flow does Na+ take?
inwards (into membrane)
What direction of flow does K+ take?
Outwards (out of cell)
What is the equation for the driving force?
Vm - Eion
Does opening of Na+ channels cause hyperpolarization or depolarization?
Depolarization.
Does opening of K+ channels cause hyperpolarization or depolarization?
Hyperpolarization.
What is the difference between leak channels and gated channels?
Leak channels are always open whereas gated channels open in response to stimulus
What are the three states of voltage-activated Na+ channels?
- Open
- closed
- Inactivated
Describe the neuronal action potential pathway employing the appropriate terms.
- At resting potential
- reaches threshold
- upstroke is the depolarisation
- overshoot is when its at its peak
- downstroke is the repolarisation
- undershoot is when it slightly hyper polarises before returning to resting potential.
What is conductance?
Conductance is a measure of conductivity; a ratio of the current flow to the difference in potential in what it is flowing through.
How long does an action potential last?
2-3 milliseconds
What type of feedback is seen when Na+ channels are activated?
Positive feedback
The activation of one channel cause further channels to open and continues depolarisation.
What type of feedback is seen when K+ channels are activated?
Negative feedback
Outward movement of K+ causes depolarisation which turns off the stimulus for opening.
Describe what refractory period means.
When voltage-gated Na+ channels enter their inactive state, waiting for repolarisation to occur to then generate another action potential.
What is the difference between the absolute and relative refractory period?
Absolute refractory period- no stimulus can elicit a second action potential (all channels inactivated)
Relative refractory period- A stronger stimulus may elicit a second action potential (some channels activated, some inactivated)
Where is the action potential initiated?
Axon Hillock.
Once active potential has been initiated at the axon hillock, further trigger stimuli are required to pass impulse down the nerve. True or false?
False.
What are the two methods used to pass impulse down nerve through propagation?
Contiguous conduction and saltatory conduction.
Describe contiguous conduction.
- occurs in unmyelinated fibres
- Like a Mexican wave
- The parts of the axon that are at resting potential before reaching the action potential, they must be depolarised first by the current flow between the activated adjacent area to the resting area.
- The action potential at the end is identical to the one at the start
Describe saltatory conduction.
- occurs in myelinated fibres
- the action potential jumps over nodes
- current flow comes from adjacent nodes
- much quicker than contiguous conduction.
What are nodes of Ranvier?
areas where there isn’t myelin sheath covering it (exposed to ECF)
