Action Potentials True or False Questions
When muscle is diseased, the number of muscle fibers in a motor unit is reduced. In an EMG, the potentials appear smaller and shorter than normal.
True
When recruited physiologically, recruitment is in order of size.
True
if the strength of the stimulus is kept the same, high excitability axons will need a very short duration pulse to reach threshold while low excitability axons will need a longer pulse to reach threshold
True
Action potentials in myelinated nerves are not regenerated. The internodes are not insulated.
False Action potentials in myelinated nerves are REGENERATED (at the nodes of Ranvier). The internodes ARE insulated.
Rheobase is the minimum current duration to excite a cell at twice the chronaxie current
False CHRONAXIE is the minimum current duration to excite a cell at twice the RHEOBASE current
Intracellular recording yield a biphasic response whereas extracellular recording yields a monophasic response
False Intracellular recording yields a MONOPHASIC response whereas extracellular recording yields a BIPHASIC response
Overall, with an increase in axon diameter: current will spread farther and slower; conduction velocity will decrease
False Overall, with an increase in axon diameter: current will spread FARTHER and FASTER. Conduction velocity will INCREASE
Chronaxie is the minimal current strength necessary to excite a cell such as a neuron or muscle fiber with essentially infinite current duration
False RHEOBASE is the minimal current strength necessary to excite a cell
The compound action potential includes several different populations of nerve fibers (some myelinated and some unmyelinated) of the same diameter
False The compound action potential includes several different populations of nerve fibers (some myelinated and some unmyelinated) of DIFFERENT DIAMETERS (and therefore different thresholds, different conduction velocities, etc) --> looks different than the AP of a single fiber
The membrane under the cathode becomes hyperpolarized.
False The membrane under the cathode becomes DEPOLARIZED.
The rapid response of the sodium channels eventually result in a net outward current [ionic level]
False The rapid response of the sodium channels eventually result in a net INWARD current
When the stimulus is passive and subthreshold, there is a large capacitive and leakage current
False When the stimulus is passive and subthreshold, there is a small capacitive and leakage current When the stimulus is above threshold, a larger depolarization results in larger capacitive and leakage currents, plus an inward current followed by an outward current
Within a given motor unit, fiber type can vary.
False Within a given motor unit, fiber type IS THE SAME.
electrotonic passive potentials are means whereby graded potentials are propagated along the membrane
False electronic passive potentials are means whereby ACTION potentials are propagated along the membrane BUT graded potentials are needed to set up the APs
In myelinated nerves, the points of action potential regeneration are all across of the nerve
False In myelinated nerves, the points of action potential regeneration are only at the nodes
Action potentials do not add together
True
As diameter increases, axial resistance decreases as the square of the diameter
True
Conduction velocity can be measured by mm/msec which yields meters/sec
True
Even for one single nerve fiber, many different sized stimuli can be a "threshold stimulus" meaning that it's just big enough to reach threshold
True
In the presence of TEA, potassium current is blocked and only the sodium current is recorded
True
In the presence of TXA, sodium current is blocked so only the potassium current is recorded
True
Increasing axon diameter reduces axial resistance and myelinated axons reduce membrane capacitance and increase membrane resistance
True
Initially, a depolarization subthreshold stimulus will cause the membrane to have initial outward current leakage. Potassium channels open slowly to cause an outward current and sodium channels open to cause an inward current [ionic level]
True
Local (passive) currents spread out from the region of active depolarization, and at each point on the membrane threshold is reached and the action potential is regenerated
True
Phases of an action potential 1. resting membrane potential 2. threshold 3. depolarization 4. peak of AP 5. repolarization 6. after hyperpolarization 7. resting
True
The clinical measurement of conduction velocity can also be measured with two sets of receptors rather than two sets of stimulating electrodes.
True
The clinical measurement of conduction velocity requires a stimulus distally, stimulus proximally, and a recording artefact
True
The compound action potential gives a series of stimuli where each stimulus is larger than the one before
True
The larger the membrane capacitance and the axial resistance, the slower the conduction velocity
True
The membrane under the anode becomes hyperpolarized.
True
The rapid depolarization is associated with a rapid increase in Na permeability and thus a rapid opening of the Na channels
True
The threshold Vm may vary. For example, it may be raised during relative refractory period.
True
The threshold stimulus can be determined by looking at a strength duration curve
True
The wave form of the recorded action potential depends on the method of recording
True
There is a delayed opening of the potassium channels. Potassium channels open and close slowly.
True
Under unphysiological conditions, the most excitable fibers are the large diameter fibers. The opposite of the size principle.
True
When a stimulus is applied and it reaches threshold, an action potential can be generated causing the polarity of the membrane to reverse, becoming momentarily positive at that location on the membrane
True
When axons are stimulated unphysiologically with extracellular electrodes, the most excitable fibers are the large diameter ones
True
