PNB 2274 EXAM QUESTIONS AND ANSWERS
Recruitment refers to:
A) Multiple twitches in one fiber of one motor unit.
B) Twitches in all the fibers of several motor units.
C) One twitch in multiple fibers of one motor unit. - Answers :B) Twitches in all the fibers
of several motor units.
One motor unit can respond with multiple twitches per stimulus.
A) True
B) False - Answers :B) False
What is the optimal sarcomere length for maximal force generation in muscle?
A) Fully stretched
B) Intermediate length
C) Completely contracted - Answers :B) Intermediate length
A single motor neuron innervates one muscle fiber.
A) True
B) False - Answers :B) False
Which of the following is NOT a mechanism of fatigue?
A) Conduction failure
B) Lactic acid buildup
C) Inhibition of cross-bridge cycling
D) Neurotransmitter breakdown - Answers :D) Neurotransmitter breakdown
In light of the "all or none" law of muscle contraction, how can you explain the graded
response? - Answers :Graded responses are the result of a change in the number of
motor units recruited. You can recruit a larger or smaller motor unit, or combine multiple
motor units to generate more force.
Define tetanus (0.5 pt). At which stimulus interval did you observe tetanus? (0.5 pt)
Explain the mechanism behind this phenomenon - Answers :Tetanus is when the action
potentials are so close together in time that it looks like a single prolonged contraction of
the motor unit. Rough tetanus was observed at 60ms and complete tetanus was at
20ms. The idea is that the contractions are so close together in time that the muscle
does not relax, and the contraction appears to be one smooth sustained contraction.
Provide a possible mechanism for why the muscle was unable to maintain a prolonged
contraction in the fatigue experiment. - Answers :Muscle fatigue can be due to a lack of
ATP. If it is not being released from the sarcoplasmic reticulum, the muscle contractions
will slowly die down.
, Does your trace roughly match with a typical length tension curve? If not, could you
provide some explanations? - Answers :Yes, my graph does roughly match the typical
length-tension curve, showing that force is greatest at "resting" length (around 4mm
here) and decreases when it is stretched too much or too little on either side of that.
"Aphid-infected plants that are exposed to ladybugs will have fewer aphids after a week
than aphid-infected plants which are left untreated. "
A) This is a good hypothesis.
B) This is a poor hypothesis because it is not testable.
C) This is a poor hypothesis because it is poorly written.
D) This is a poor hypothesis because it is not true. - Answers :A) This is a good
hypothesis.
During reciprocal activation, why is the antagonist muscle not completely silent? -
Answers :Because it is used to stabilize the joint
1. Unlike the discrete waveform from an electrocardiogram, the electromyogram
waveform is irregular. Why do you suppose this is? - Answers :Electrocardiograms are
smooth and waveform because the cardiac muscle contracts in a smooth synchronous
way. Voluntary muscle on the other hand, such as skeletal muscle with an
electromyogram is contracted in an irregular way due to the unsynchronized recruitment
of separate motor units by different nerves and unsynchronized firing of each neuron.
Which of the following statements about electromyography (EMG) recording is NOT
true?
A) Attaching electrodes to hairy or bony area on the skin will give bad electrical contact.
B) EMG is a technique that measures the contractile force of the muscles.
C) The signal recorded by EMG is from multiple muscle fibers.
D) In our experiment, integrated instead of raw data is used for value measurement. -
Answers :B) EMG is a technique that measures the contractile force of the muscles.
3. Based on your recorded EMG trace and the values you measured in Exercise 1,
describe this phenomenon qualitatively. - Answers :Reciprocal activation is a
phenomenon that happens when you contract a muscle, the antagonist muscle will
show a much lower EMG reading than the primary muscle being contracted. This is
shown in our bicep contraction section, where the bicep trace is much higher than the
tricep trace.
4. In your own words, explain how the EMG trace changed when you added weights to
your arm? Based on the data you collected what can you infer is happening to the
muscles as weight is added? - Answers :The bicep muscle must be the muscle involved
in holding up the weight, because the amplitude of the bicep trace consistently
increased with increased weight, while the tricep remained relatively constant. As we
add more weight, the recruitment of muscle units or muscle fibers of the bicep must be
increasing.
Recruitment refers to:
A) Multiple twitches in one fiber of one motor unit.
B) Twitches in all the fibers of several motor units.
C) One twitch in multiple fibers of one motor unit. - Answers :B) Twitches in all the fibers
of several motor units.
One motor unit can respond with multiple twitches per stimulus.
A) True
B) False - Answers :B) False
What is the optimal sarcomere length for maximal force generation in muscle?
A) Fully stretched
B) Intermediate length
C) Completely contracted - Answers :B) Intermediate length
A single motor neuron innervates one muscle fiber.
A) True
B) False - Answers :B) False
Which of the following is NOT a mechanism of fatigue?
A) Conduction failure
B) Lactic acid buildup
C) Inhibition of cross-bridge cycling
D) Neurotransmitter breakdown - Answers :D) Neurotransmitter breakdown
In light of the "all or none" law of muscle contraction, how can you explain the graded
response? - Answers :Graded responses are the result of a change in the number of
motor units recruited. You can recruit a larger or smaller motor unit, or combine multiple
motor units to generate more force.
Define tetanus (0.5 pt). At which stimulus interval did you observe tetanus? (0.5 pt)
Explain the mechanism behind this phenomenon - Answers :Tetanus is when the action
potentials are so close together in time that it looks like a single prolonged contraction of
the motor unit. Rough tetanus was observed at 60ms and complete tetanus was at
20ms. The idea is that the contractions are so close together in time that the muscle
does not relax, and the contraction appears to be one smooth sustained contraction.
Provide a possible mechanism for why the muscle was unable to maintain a prolonged
contraction in the fatigue experiment. - Answers :Muscle fatigue can be due to a lack of
ATP. If it is not being released from the sarcoplasmic reticulum, the muscle contractions
will slowly die down.
, Does your trace roughly match with a typical length tension curve? If not, could you
provide some explanations? - Answers :Yes, my graph does roughly match the typical
length-tension curve, showing that force is greatest at "resting" length (around 4mm
here) and decreases when it is stretched too much or too little on either side of that.
"Aphid-infected plants that are exposed to ladybugs will have fewer aphids after a week
than aphid-infected plants which are left untreated. "
A) This is a good hypothesis.
B) This is a poor hypothesis because it is not testable.
C) This is a poor hypothesis because it is poorly written.
D) This is a poor hypothesis because it is not true. - Answers :A) This is a good
hypothesis.
During reciprocal activation, why is the antagonist muscle not completely silent? -
Answers :Because it is used to stabilize the joint
1. Unlike the discrete waveform from an electrocardiogram, the electromyogram
waveform is irregular. Why do you suppose this is? - Answers :Electrocardiograms are
smooth and waveform because the cardiac muscle contracts in a smooth synchronous
way. Voluntary muscle on the other hand, such as skeletal muscle with an
electromyogram is contracted in an irregular way due to the unsynchronized recruitment
of separate motor units by different nerves and unsynchronized firing of each neuron.
Which of the following statements about electromyography (EMG) recording is NOT
true?
A) Attaching electrodes to hairy or bony area on the skin will give bad electrical contact.
B) EMG is a technique that measures the contractile force of the muscles.
C) The signal recorded by EMG is from multiple muscle fibers.
D) In our experiment, integrated instead of raw data is used for value measurement. -
Answers :B) EMG is a technique that measures the contractile force of the muscles.
3. Based on your recorded EMG trace and the values you measured in Exercise 1,
describe this phenomenon qualitatively. - Answers :Reciprocal activation is a
phenomenon that happens when you contract a muscle, the antagonist muscle will
show a much lower EMG reading than the primary muscle being contracted. This is
shown in our bicep contraction section, where the bicep trace is much higher than the
tricep trace.
4. In your own words, explain how the EMG trace changed when you added weights to
your arm? Based on the data you collected what can you infer is happening to the
muscles as weight is added? - Answers :The bicep muscle must be the muscle involved
in holding up the weight, because the amplitude of the bicep trace consistently
increased with increased weight, while the tricep remained relatively constant. As we
add more weight, the recruitment of muscle units or muscle fibers of the bicep must be
increasing.
