PNB 2264 Lab Practical #2 Study
Guide Questions With 100% Correct
Answers 2026/2027 Updated.
How can the force of contraction be increased in muscle fibers? - Answer By increasing the
stimulus frequency
What is the experimental set up for the frog experiment? - Answer 1. Secure the femur in the
femur clamp of the ring stand. Slide the femur into the tygon-tubing collar and tighten the
screw. It is best to have the knee placed upside down
2. Tighten the thumbscrew until the femur is set firmly in the clamp. The tubing collar serves
two purposes; prevents the bone from being crushed and insulates any muscle tissue from
reacting with the metal clamp
3. Adjust the height of the transducer so that the thread connecting the muscle prep to the
transducer has slight tension on it and the muscle and thread are as vertical as possible
4. Position the stimulating electrode (on ring stand #2) so that the two electrode wires just
press into the belly portion of the gastrocnemius muscle
What is the calibration procedure for the frog experiment? - Answer 1. Click start and record
for about 5 seconds
2. Balance a 5-gram weight on top of the pin of the force transducer and record for another 5
seconds
3. Enter the weight in the unit conversion table in the appropriate cell to calculate the force (N)
value
4. Use waveform cursor to select a stable section of the record before you added the weight,
then click the arrow next to point 1 in the calibration panel and if it is not already entered, type
0 in the right-hand box
5. Select a stable section of the record after you added the weight, click the arrow next to point
2 and enter the calculated N value
What are each of the steps on the muscle contraction graph? - Answer 1. Twitch
2. Summation
,3. (Unfused) Tetanus
4. (Fused) Tetanus
5. Fatigue
What is a muscle twitch? - Answer A single contraction in a relaxation cycle observed in a
musculoskeleton fiber
What is summation? - Answer Applying multiple stimulus within a short duration (especially
when effect from a previous stimulus has not completely disappeared) an increase in contractile
force is visible
What is tetanus? - Answer When muscle fiber contraction reach a point where they remain
constant. When the stimulus frequency increases, the muscle fibers don't have time to relax and
their contractile forces fuze together
What is muscle fatigue and why does it occur? - Answer The decline in ability of a muscle to
generate force. It occurs because of conduction failure, lactic acid buildup, and inhibition of
cross bridge cycling
What is the first step of cross bridge cycling? - Answer Cross bridge formation:
phosphorylated myosin head attaches to an actin myofilament
What is the second step of cross bridge cycling? - Answer the power stroke:
1) ADP and Pi are released from the myosin head
2) Myosin head changes to bend, low-energy state
3) Shape change pulls the actin towards the M line
What is the third step of cross bridge cycling? - Answer Cross bridge detachment: ATP
attaches to myosin, breaking the cross bridge
What is the fourth step of cross bridge cycling? - Answer Cocking of the myosin head:
attached ADP is hydrolyzed by myosin ATPase into ADP + Pi, bringing it back to a high-energy
state
As you increase voltage to the muscle fibers, describe how they respond to the increased
stimulus - Answer As the voltage is increased, the muscle contractions will increase up to a
certain point
, What is the Maximum Excitation Voltage? - Answer The stimulus voltage at which the
response no longer increases
What is supra maximal voltage? - Answer A stimulus that has the strength significantly above
that required to activate all the nerve or muscle fibers in contact with the electrode; used when
response of all the fibers is desired
Describe how the isolated frog muscle behaved as the stimulus interval was decreased
progressively - Answer As the stimulus interval was decreased, the muscle twitches became
less pronounced with smaller time intervals between twitches
What is the all-or-none phenomenon? - Answer The strength at which a nerve or muscle
fiber responds to a stimulus is independent of the strength of the stimulus. If the stimulus
exceeds the threshold potential, the nerve or muscle fiber will give a complete response;
otherwise, there is no response
In light of the all-or-none law of muscle contraction, how can you explain graded potential? -
Answer The all-or-none phenomenon regarding muscle contractions involves the idea that no
matter how intense the stimulus, as long as membrane potential reaches threshold, an action
potential will fire without variations to the intensity.
Graded response on the other hand involves muscles responding with different degrees of force
due to recruitment of multiple motor units, stimulus intensity, frequency and length-tension
curve. All of these things acting together give a graded response of the muscle fibers
What is muscle recruitment? - Answer Activation of additional motor units to accomplish an
increase in contractile strength in a muscle.
The higher the recruitment, the stronger the muscle contraction will be.
How does resting fiber length affect muscle tension? - Answer If you have a very stretched
out muscle, there will be little crossover between filaments leading to very little force being
generated
Optimal length is when you have maximum cross bridges between thin and thick filaments
Too much overlap is not good or effective
Which sacromere represents optimal muscle length and will generate he strongest tension
shown in the length-tension curve? - Answer Sacromere C
Guide Questions With 100% Correct
Answers 2026/2027 Updated.
How can the force of contraction be increased in muscle fibers? - Answer By increasing the
stimulus frequency
What is the experimental set up for the frog experiment? - Answer 1. Secure the femur in the
femur clamp of the ring stand. Slide the femur into the tygon-tubing collar and tighten the
screw. It is best to have the knee placed upside down
2. Tighten the thumbscrew until the femur is set firmly in the clamp. The tubing collar serves
two purposes; prevents the bone from being crushed and insulates any muscle tissue from
reacting with the metal clamp
3. Adjust the height of the transducer so that the thread connecting the muscle prep to the
transducer has slight tension on it and the muscle and thread are as vertical as possible
4. Position the stimulating electrode (on ring stand #2) so that the two electrode wires just
press into the belly portion of the gastrocnemius muscle
What is the calibration procedure for the frog experiment? - Answer 1. Click start and record
for about 5 seconds
2. Balance a 5-gram weight on top of the pin of the force transducer and record for another 5
seconds
3. Enter the weight in the unit conversion table in the appropriate cell to calculate the force (N)
value
4. Use waveform cursor to select a stable section of the record before you added the weight,
then click the arrow next to point 1 in the calibration panel and if it is not already entered, type
0 in the right-hand box
5. Select a stable section of the record after you added the weight, click the arrow next to point
2 and enter the calculated N value
What are each of the steps on the muscle contraction graph? - Answer 1. Twitch
2. Summation
,3. (Unfused) Tetanus
4. (Fused) Tetanus
5. Fatigue
What is a muscle twitch? - Answer A single contraction in a relaxation cycle observed in a
musculoskeleton fiber
What is summation? - Answer Applying multiple stimulus within a short duration (especially
when effect from a previous stimulus has not completely disappeared) an increase in contractile
force is visible
What is tetanus? - Answer When muscle fiber contraction reach a point where they remain
constant. When the stimulus frequency increases, the muscle fibers don't have time to relax and
their contractile forces fuze together
What is muscle fatigue and why does it occur? - Answer The decline in ability of a muscle to
generate force. It occurs because of conduction failure, lactic acid buildup, and inhibition of
cross bridge cycling
What is the first step of cross bridge cycling? - Answer Cross bridge formation:
phosphorylated myosin head attaches to an actin myofilament
What is the second step of cross bridge cycling? - Answer the power stroke:
1) ADP and Pi are released from the myosin head
2) Myosin head changes to bend, low-energy state
3) Shape change pulls the actin towards the M line
What is the third step of cross bridge cycling? - Answer Cross bridge detachment: ATP
attaches to myosin, breaking the cross bridge
What is the fourth step of cross bridge cycling? - Answer Cocking of the myosin head:
attached ADP is hydrolyzed by myosin ATPase into ADP + Pi, bringing it back to a high-energy
state
As you increase voltage to the muscle fibers, describe how they respond to the increased
stimulus - Answer As the voltage is increased, the muscle contractions will increase up to a
certain point
, What is the Maximum Excitation Voltage? - Answer The stimulus voltage at which the
response no longer increases
What is supra maximal voltage? - Answer A stimulus that has the strength significantly above
that required to activate all the nerve or muscle fibers in contact with the electrode; used when
response of all the fibers is desired
Describe how the isolated frog muscle behaved as the stimulus interval was decreased
progressively - Answer As the stimulus interval was decreased, the muscle twitches became
less pronounced with smaller time intervals between twitches
What is the all-or-none phenomenon? - Answer The strength at which a nerve or muscle
fiber responds to a stimulus is independent of the strength of the stimulus. If the stimulus
exceeds the threshold potential, the nerve or muscle fiber will give a complete response;
otherwise, there is no response
In light of the all-or-none law of muscle contraction, how can you explain graded potential? -
Answer The all-or-none phenomenon regarding muscle contractions involves the idea that no
matter how intense the stimulus, as long as membrane potential reaches threshold, an action
potential will fire without variations to the intensity.
Graded response on the other hand involves muscles responding with different degrees of force
due to recruitment of multiple motor units, stimulus intensity, frequency and length-tension
curve. All of these things acting together give a graded response of the muscle fibers
What is muscle recruitment? - Answer Activation of additional motor units to accomplish an
increase in contractile strength in a muscle.
The higher the recruitment, the stronger the muscle contraction will be.
How does resting fiber length affect muscle tension? - Answer If you have a very stretched
out muscle, there will be little crossover between filaments leading to very little force being
generated
Optimal length is when you have maximum cross bridges between thin and thick filaments
Too much overlap is not good or effective
Which sacromere represents optimal muscle length and will generate he strongest tension
shown in the length-tension curve? - Answer Sacromere C
