Membrane Potential / Action Potential

Question 1

What are the main ions involved in action potentials and maintaining membrane potential?

Answer 1

Na+, K+, Cl-, (minorly - Ca2+)

Question 2

What is the charge on the inside of the cell?

Answer 2

Negative: attracts K+ ions in

Question 3

What is the charge on the outside of the cell?

Answer 3

Positive

Question 4

When can the concentration of K+ change outside the cell?

Answer 4

During an epileptic tonic-clonic seizure, the synchronous release of K+ to outside the cell

Question 5

How can a seizure spread?

Answer 5

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

Question 6

What does the Na+—K+ pump do?

Answer 6

It moves Na+ out of the cell while moving K+ into it, by the hydrolysis of ATP

Question 7

How is the Na+—K+ pump stimulated?

Answer 7

By increased Na+ in the cell

Question 8

What is the rate for the Na+–K+ pump?

Answer 8

3Na+ out for 2K+ in

Question 9

What is the cause of a membrane potential?

Answer 9

ion concentration gradients across the membrane (maintained by active transport systems, e.g. the Na/K ATPase)

Question 10

If a membrane is permeable to 2 ions, what will determine the resting potential of the membrane?

Answer 10

Its value will be determined by the relative permeability of the membrane to these two ions.

Question 11

Who measured the first AP?

Answer 11

Hodgkin and Huxley in a squid axon: it was big so faster action potentials

Question 12

What is an action potential?

Answer 12

A rapid depolarization (positive) followed by repolarization (and then hyperpolarization) of the membrane potential

Question 13

What is the voltage-clamp technique?

Answer 13

applying a set voltage to a cell while simultaneously measuring the resulting currents flowing through the membrane.

Question 14

What does Tetrodotoxin (TTX) do?

Answer 14

Selectively blocks voltage-dependent Na+ currents

Question 15

Why is tetrodotoxin useful?

Answer 15

You can selectively isolate K+ currents and examine its voltage dependence and time course

Question 16

What is Tetraethylammonium (TEA)?

Answer 16

Selectively blocks K+ currents

Question 17

What are the fundamental properties of Na+ and K+ currents?

Answer 17

• Na+ current rapidly activates and inactivates.
• K+ current slowly activates and remains sustained once activated

Question 18

Describe in detail the steps of an action potential

Answer 18

1. Depolarization of the membrane increases chance of Na+ going into cell
2. One action potential threshold is reached (-55mV) Na+ ions move into cell
3. This causes more Na+ channels to open and then more depolarization
4. As more of these channels activate the original ones are becoming inactive
5. the K+ channels are opening now and K+ is leaving the cell
6. Peak of AP is when Na+ movement in is equal to K+ movement out
7. K+ then continues moving out and cell is repolarised
8. K+ continues for a few milliseconds which leads to hyperpolarization (refractory period)
   9.

Question 19

Where do APs originate?

Answer 19

the initial portion of the axon (top of it)

Question 20

How do APs travel?

Answer 20

down the axon to the synaptic terminal where neurotransmitters are released and start the next AP in the next neuron

Question 21

What are the nodes of Ranvier?

Answer 21

gaps formed between the myelin sheath where the axons are left uncovered

Question 22

What can increase the speed of APs?

Answer 22

Myelin sheaths on an axon

Question 23

How can myelination affect disease?

Answer 23

Example: in MS, demyelination is thought to prevent APs

Question 24

What is ADPEAF

Answer 24

Autosomal dominant lateral temporal lobe epilepsy
with auditory features

Question 25

50% of ADPEAF patients
have mutations where?

Answer 25

In the leucine-rich glioma inactivated
gene 1 (LGI1)

Question 26

What do the mutations do?

Answer 26

Disease-causing mutations in the
Lgi1 protein render it unable to prevent fast inactivation of presynaptic KV1.1 currents.

Question 27

What is ion selectivity of ion channels influenced by?

Answer 27

1. pore diameter
2. Nature of the residue lining the pore

Question 28

What is the mechanisms of local anesthetic?

Answer 28

It binds to the intracellular portion of the VGSC when open and then blocks the channel preventing APs

Question 29

Who was the voltage clamp invented by?

Answer 29

Kenneth Cole

Question 30

What is an advantage of the voltage clamp?

Answer 30

It allows ionic and capacitive components to be analyzed separately