The Action Potential Flashcards
The action potential is unique to these cells
neurons, muscle, and neuroendocrine cells
In most nerve cells at rest, the membrane potential is about ____.
-60 mV
Hyperpolarization
Making the membrane more negative (increasing the membrane potential)
Depolarization
Decrease in the membrane potential (makes the membrane more positive)
Typically, the membrane must be depolarized by about _____ in order for an action potential to be triggered.
10 to 20 mV
True or false. The amplitude of the action potential is independent of the strength of the stimulus.
True.
The ______, however, is a function of stimulus strength.
frequency of discharge
Have an understanding of what overshoot and undershoot are.
After an action potential, the cell is positive (overshoot) then it returns to normal and becomes more negative than normal (undershoot)
Absolute refractory period
Brief period during which time it is impossible to make the neuron fire another action potential. Usually lasts about 1 ms. ( Limits maximum firing rate to ~1000 Hz.)
Methods for measuring the membrane potential and the current necessary to maintain the potential
Voltage clamp technique: Electrode inside cell measures membrane potential and compares to “command voltage” or desired membrane voltage. Difference in voltage is passed back into the cell (error signal) to set the membrane potential to the command voltage. The amount of current necessary to maintain this voltage is monitored.
Whole-cell patch clamp recording records membrane potential and current needed to keep the membrane potential equal to the desired membrane voltage.
There is no ____ when Em is clamped at +55mV.
inward current
The early inward current is carried by entry of ___ across the membrane.
Sodium ions
Tetrodoxin
An alkaloid neurotoxin that blocks sodium currents while potassium currents remain
Tetraethylammonium
Selectively blocks potassium currents while the sodium currents remain
Membrane conductance is the reciprocal of ___.
Membrane resistance
Equation of membrane conductance
gion = ionic current / (membrane potential - equilibrium potential for the ion flowing with conductance gion)
(The difference betwee the two potentials is the electrochemical driving force acting on the ion)
What is important to know about sodium and potassium membrane conductance?
Both gNa and gK are voltage dependent. The conductance increases progressively as the neuron is depolarized.
Both conductances change over time. Both require time to activate, and the inward flow of sodium precedes the outward flow of potassium.
____ is responsible for action potential generation.
A selective increase in the membrane conductance of sodium
Membrane potential for sodium (value)
58 mV
Membrane potential for potassium (value)
-81mV
Membrane potential for chloride (value)
-86mV
The membrane conductance of potassium is responsible for ____.
Restoring the resting membrane potential, also responsible for undershoot.
The effect of depolarization on sodium conductance is ____.
regenerative
The voltage dependence of potassium conductance is ____ and involves ____.
self-limiting,
negative feedback
