Electrophysiology Flashcards
What is the (resting) membrane potential?
Difference between the electric potential in the intracellular and extracellular matrices of the cell when it isn’t excited.
Where does membrane potential originate from?
The different concentrations of ions (expressed in mmol/l) at the inner and outer surface of the cell membrane.
What are the four excitable tissues in the body and what are their EM values?
Skeletal muscle cell = -90 millivolts (mV)
Smooth muscle cell = -55mV
Cardiac muscle cell = -80mV
Neuron = -65mV
Does every cell have a membrane potential?
Yes
What can change the membrane potential and generate an action potential?
Excitable cells - nerves and muscles
What is meant by electronegativity?
Describing elements that tend to gain electrons and form negative ions.
What is meant by electropositivity?
Tending to lose electrons and form positive ions in chemical reactions.
What do negative values of the membrane potentials indicate?
The cytoplasm is more electronegative than the extracellular space.
What does the value of the membrane potential depend on?
Concentration of ions inside and outside the cell.
Activity of the sodium-potassium pump.
Variable permeability of the cell membrane for ions.
What ions contribute to the value of the membrane potential the most?
Sodium, potassium, calcium, and chloride ions.
What happens in the NA-K pump?
Uses energy to expel 3 molecules of sodium in exchange for 2 molecules of potassium.
Why is the sodium potassium pump important?
Creates concentration gradients for sodium and potassium, allowing more sodium in the extracellular space, and more potassium in the intracellular space.
What type of signals are action potentials?
Nerve cells
What are the three phases and two stages of action potentials?
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.
What is hyper-polarisation?
Initial increase of the membrane potential to the value of the threshold potential.
What happens in depolarisation?
The threshold potential opens voltage-gated sodium channels and causes a large influx of sodium ions.
Does the inside of the cell become more positive or negative during depolarisation?
More electropositive, until the potential gets closer the electrochemical equilibrium for sodium of +61 mV.
What is the overshoot phase?
Phase of extreme positivity
What happens to sodium permeability after the overshoot phase and why?
Sodium permeability suddenly decreases due to the closing of its channels.
What happens in repolarisation?
The overshoot value of the cell potential opens voltage-gated potassium channels, which causes a large potassium efflux, decreasing the cell’s electropositivity.
What is the purpose of repolarisation?
Restore the resting membrane potential
What does repolarisation lead to?
Hyperpolarization then the membrane establishes again the values of membrane potential.
What is hyperpolarisation?
A state in which the membrane potential is more negative than the default membrane potential
What is the refractory period?
Time after an action potential is generated, during which the excitable cell cannot produce another action potential.
What does excitation-contraction coupling refer to?
Rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction.
