Membrane Potential / Action Potential Flashcards
(31 cards)
What are the main ions involved in action potentials and maintaining membrane potential?
Na+, K+, Cl-, (minorly - Ca2+)
What is the charge on the inside of the cell?
Negative: attracts K+ ions in
What is the charge on the outside of the cell?
Positive
When can the concentration of K+ change outside the cell?
During an epileptic tonic-clonic seizure, the synchronous release of K+ to outside the cell
How can a seizure spread?
This shift in the equilibrium potential (K+) can
increase the excitability of affected neurons and
neuronal processes and thus promote the spread of
the seizure activity
What does the Na+—K+ pump do?
It moves Na+ out of the cell while moving K+ into it, by the hydrolysis of ATP
How is the Na+—K+ pump stimulated?
By increased Na+ in the cell
What is the rate for the Na+–K+ pump?
3Na+ out for 2K+ in
What is the cause of a membrane potential?
ion concentration gradients across the membrane (maintained by active transport systems, e.g. the Na/K ATPase)
If a membrane is permeable to 2 ions, what will determine the resting potential of the membrane?
Its value will be determined by the relative permeability of the membrane to these two ions.
Who measured the first AP?
Hodgkin and Huxley in a squid axon: it was big so faster action potentials
What is an action potential?
A rapid depolarization (positive) followed by repolarization (and then hyperpolarization) of the membrane potential
What is the voltage-clamp technique?
applying a set voltage to a cell while simultaneously measuring the resulting currents flowing through the membrane.
What does Tetrodotoxin (TTX) do?
Selectively blocks voltage-dependent Na+ currents
Why is tetrodotoxin useful?
You can selectively isolate K+ currents and examine its voltage dependence and time course
What is Tetraethylammonium (TEA)?
Selectively blocks K+ currents
What are the fundamental properties of Na+ and K+ currents?
- Na+ current rapidly activates and inactivates.
- K+ current slowly activates and remains sustained once activated
Describe in detail the steps of an action potential
- Depolarization of the membrane increases chance of Na+ going into cell
- One action potential threshold is reached (-55mV) Na+ ions move into cell
- This causes more Na+ channels to open and then more depolarization
- As more of these channels activate the original ones are becoming inactive
- the K+ channels are opening now and K+ is leaving the cell
- Peak of AP is when Na+ movement in is equal to K+ movement out
- K+ then continues moving out and cell is repolarised
- K+ continues for a few milliseconds which leads to hyperpolarization (refractory period)
9.
Where do APs originate?
the initial portion of the axon (top of it)
How do APs travel?
down the axon to the synaptic terminal where neurotransmitters are released and start the next AP in the next neuron
What are the nodes of Ranvier?
gaps formed between the myelin sheath where the axons are left uncovered
What can increase the speed of APs?
Myelin sheaths on an axon
How can myelination affect disease?
Example: in MS, demyelination is thought to prevent APs
What is ADPEAF
Autosomal dominant lateral temporal lobe epilepsy
with auditory features
