Flashcards in Introduction to Electrophysiology Deck (13):
What is resting potential vs threshold potential?
Resting potential - normal state of cell, around -60 mV
Threshold potential - Excitatory synaptic input will cause depolarization. When reaching this threshold, an action potential will commence
What is meant by "overshoot" of action potential? How long is an action potential?
Peaks of action potentials are over 0 mV. An action potential is around 1 ms for most neurons
What is the after-hyperpolarization and what causes it?
Membrane potential is temporarily more negative than the resting potential, due to rush of potassium ions out of the cell from voltage-gated potassium channels, again making the membrane very negative
What causes the peak of the action potential? How does reduction of extracellular sodium affect a cell?
Peak is sodium dependent, caused by voltage-gated sodium channels opening, allowing Na+ influx to increase the charge inside the cell. Reduction of external sodium gradient will reduce the peak of action potential, but does not affect the resting potential or after polarization (controlled by K+)
What are distinguishing characteristics of pacemaker cells?
Long action potentials -> 100 ms spikes.
Still overshoots 0 mV
Spontaneously active, membrane potentially never really comes to rest. Just goes back to increasing until triggering a spike at threshold potential
What is conductance?
The inverse of resistance. 1/G = R. It is promoted by opening channels.
Ohm's law is I = V*G
This makes sense, because to have the same current with less voltage you would need a greater conductance
What is the equilibrium potential and what is it dependent on?
The value of the voltage whereby the amount of ion flow in one direction due to the concentration gradient is equal to the amount of flow in the opposite direction due to the electric field
Dependent on the ratio of concentrations of the permeate ion (greater gradients will allow for larger voltages pushing back to balance them)
What equation describes the voltage across a membrane as a function of the ion ratios in and out? What are typical 2-fold, 10-fold, and 20-fold values?
Nernst equation. At 37 degrees C
2 fold: -18 mV
10 fold: -62 mV
20 fold: -80 mV
How is membrane potential affected when there are multiple ions?
ions with greater permeability / membrane conductance will have a greater contribution to the resting membrane potential than those with low permeability / membrane conductance.
Membrane is most permeable to potassium -> primarily decides resting membrane potential.
What ions decide the resting membrane potential, and is this at equilibrium? How is it controlled?
Membrane is highly permeable to potassium, which would have a Nernst equilibrium at -90 mV
Na+ is less permeable, would have equilibrium at +55 mV given the concentrations
Cl- is passively distributed, and its equilibrium is around -70 mV
It is a non-equilibrium situation -> potassium and sodium leak because neither is at equilibrium. This must be maintained in a steady state by Na+/K+ ATPase
What are the Hodgkin-Huxley and the Goldman-Hodgkin-Katz equations?
Equations that calculate the membrane potential.
HH: Uses membrane conductance of specific ions to show contributing portions
GHK: Uses various ion permeabilities and concentrations, basically equivalent
Why is an Na/K-ATPase required to maintain a gradient?
Since the membrane potential is a sum of each individual ionic potential, the ions are not each at their electrical equilibrium. Electrical equilibrium for potassium would be at -90 mV, but the cell is only at -65 mV. Thus, potassium still has a tendency to leak out, and sodium has a tendency to leak in (its equilibrium is +55 mV). Overtime, the chemical gradients would be destroyed if not maintained by the ATPase