Electrophysiology

Question 1

What is the (resting) membrane potential?

Answer 1

Difference between the electric potential in the intracellular and extracellular matrices of the cell when it isn’t excited.

Question 2

Where does membrane potential originate from?

Answer 2

The different concentrations of ions (expressed in mmol/l) at the inner and outer surface of the cell membrane.

Question 3

What are the four excitable tissues in the body and what are their EM values?

Answer 3

Skeletal muscle cell = -90 millivolts (mV)

Smooth muscle cell = -55mV

Cardiac muscle cell = -80mV

Neuron = -65mV

Question 4

Does every cell have a membrane potential?

Answer 4

Yes

Question 5

What can change the membrane potential and generate an action potential?

Answer 5

Excitable cells - nerves and muscles

Question 6

What is meant by electronegativity?

Answer 6

Describing elements that tend to gain electrons and form negative ions.

Question 7

What is meant by electropositivity?

Answer 7

Tending to lose electrons and form positive ions in chemical reactions.

Question 8

What do negative values of the membrane potentials indicate?

Answer 8

The cytoplasm is more electronegative than the extracellular space.

Question 9

What does the value of the membrane potential depend on?

Answer 9

Concentration of ions inside and outside the cell.

Activity of the sodium-potassium pump.

Variable permeability of the cell membrane for ions.

Question 10

What ions contribute to the value of the membrane potential the most?

Answer 10

Sodium, potassium, calcium, and chloride ions.

Question 11

What happens in the NA-K pump?

Answer 11

Uses energy to expel 3 molecules of sodium in exchange for 2 molecules of potassium.

Question 12

Why is the sodium potassium pump important?

Answer 12

Creates concentration gradients for sodium and potassium, allowing more sodium in the extracellular space, and more potassium in the intracellular space.

Question 13

What type of signals are action potentials?

Answer 13

Nerve cells

Question 14

What are the three phases and two stages of action potentials?

Answer 14

An action potential has three phases: depolarization, overshoot, repolarization.

The first one is hypopolarization which precedes the depolarization, while the second one is hyperpolarization, which follows the repolarization.

Question 15

What is hyper-polarisation?

Answer 15

Initial increase of the membrane potential to the value of the threshold potential.

Question 16

What happens in depolarisation?

Answer 16

The threshold potential opens voltage-gated sodium channels and causes a large influx of sodium ions.

Question 17

Does the inside of the cell become more positive or negative during depolarisation?

Answer 17

More electropositive, until the potential gets closer the electrochemical equilibrium for sodium of +61 mV.

Question 18

What is the overshoot phase?

Answer 18

Phase of extreme positivity

Question 19

What happens to sodium permeability after the overshoot phase and why?

Answer 19

Sodium permeability suddenly decreases due to the closing of its channels.

Question 20

What happens in repolarisation?

Answer 20

The overshoot value of the cell potential opens voltage-gated potassium channels, which causes a large potassium efflux, decreasing the cell’s electropositivity.

Question 21

What is the purpose of repolarisation?

Answer 21

Restore the resting membrane potential

Question 22

What does repolarisation lead to?

Answer 22

Hyperpolarization then the membrane establishes again the values of membrane potential.

Question 23

What is hyperpolarisation?

Answer 23

A state in which the membrane potential is more negative than the default membrane potential

Question 24

What is the refractory period?

Answer 24

Time after an action potential is generated, during which the excitable cell cannot produce another action potential.

Question 25

What does excitation-contraction coupling refer to?

Answer 25

Rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction.