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Posts: 1
5 years ago
I am having a tough time with this lab because I was never very good at chemistry, and this seems to be all about that. Is there an answer key to check my answers with?
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12 Replies
5 years ago
Please post the question.
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5 years ago
hope this helps
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5 years ago
This probably just saved my grade. Thank you for the help. Grinning Face
elsiebaybee,  samozega
5 years ago
Thank you, very much appreciated!
5 years ago
Thanks slabbapop. You helped very much!
5 years ago Edited: 5 years ago, Blinmalina
This is an Exercise 2, if anyone interested. 48 questions and 48 answers:
_____________________________ _____________________________

1.   The latent period of the skeletal muscle that was tested in this lab simulation was
a.   about 1 second.
b.   less than 1 msec.              
c.   between 2-3 msec.
d.   variable, depending on the voltage that was applied to it.
2.   True or False:  Another name for a muscle cell is “myofibril.”  
3.   The largest active force that could be generated in the muscle is Activity 1 was _______ grams.
4.   Define the terms skeletal muscle fiber, motor unit, skeletal muscle twitch, electrical stimulus, and latent period.
5.   What is the role of acetylcholine (ACh) in a skeletal muscle contraction?
6.   Describe the process of excitation-contraction coupling in skeletal muscle fibers.
7.   Describe the three phases of a skeletal muscle twitch.
8.   Does the duration of the latent period change with different stimulus voltages?
9.   At the threshold stimulus, do sodium ions start to move into or out of the cell to bring about the membrane depolarization?
ACTIVITY 2:  The Effect of Stimulus Voltage on Skeletal Muscle Contraction
10.   The threshold voltage for the muscle in this lab simulation was ________ volts.  When that voltage was used to stimulate the muscle, ________ grams of active force were generated.
11.   True or False:  In a resting skeletal muscle cell, most of the calcium ions freely move through the cytoplasm of the cell.  
12.   Describe the effect of increasing stimulus voltage on isolated skeletal muscle.  Specifically, what happened to the muscle force generated with stronger electrical stimulations and why did this change occur?
13.   How is this change in whole-muscle force achieved in vivo (eg. in the human body)?
14.   What happened in the isolated skeletal muscle when the maximal voltage was applied?
ACTIVITY 3:  The Effect of Stimulus Frequency on Skeletal Muscle Contraction
15.   True or False:  There is no limit to the amount of force that a skeletal muscle can generate if it is stimulated by a high enough voltage at a very high frequency.
16.   The chemical ion or molecule that is primarily responsible for initiating the contraction of a muscle fiber is
a.   Na+
b.   K+            
c.   Ca2+
d.   ADP
17.   What is the difference between stimulus intensity and stimulus frequency?
18.   In this experiment you observed the effect of stimulating the isolated skeletal muscle multiple times in a short period with complete relaxation between the stimuli.  Describe the force of contraction with each subsequent stimulus.  Is this called treppe or wave summation?
19.   How did the frequency of stimulation affect the amount of force generated by the isolated skeletal muscle when the frequency of stimulation was increased such that the muscle twitches did not fully relax between subsequent stimuli?  Is this called treppe or wave summation?
20.   To achieve an active force of 5.2 g, did you have to increase the stimulus voltage above 8.5 volts? If not, how did you achieve an active force of 5.2 g?
ACTIVITY 4:  Tetanus in Isolated Skeletal Muscle
21.   When stimuli were applied to the muscle frequently enough to cause a plateau in the amount of force generated, a state known as ____________  ____________ occurs.
22.   Why do children (and adults) receive an immunization (actually several!) called a “tetanus shot”?
a.   This will prevent the development of muscle fatigue when she/he becomes an athlete.
b.   The person will then be able to develop the maximum amount of force from each and every muscle in her/his body.
c.   To prevent the development of a condition called “lockjaw” that can develop from a specific bacterial infection.
d.   This will a reminder to her/him to keep the skin washed and clean when she/he is outside playing.
23.   The maximal tetanic tension of the muscle in this simulation was _________ grams.
24.   Describe how increasing the stimulus frequency affected the force developed by the isolated whole skeletal muscle in this activity.
25.   Indicate what type of force was developed by the isolated skeletal muscle in this activity at the following stimulus frequencies: at 50 stimuli/second, at 140 stimuli/second, and above 146 stimuli/second.
26.   Beyond what stimulus frequency is there no further increase in the peak force?  What is the muscle tension called at this frequency?
ACTIVITY 5:  Fatigue in Isolated Skeletal Muscle
27.   True or False:  The primary reason for muscle fatigue is the buildup of Ca2+ ions in the muscle fiber.
28.   If an intervening rest period is imposed on active muscle,
a.   it will then be able to generate much more force.
b.   the development of fatigue will be delayed.      
c.   muscle hypertrophy can be prevented.
d.   muscle atrophy can be prevented.
29.   When a skeletal muscle fatigues, what happens to the contractile force over time?  
30.   What are some proposed causes of skeletal muscle fatigue?
31.   Turing the stimulator off allows a small measure of muscle recovery.  Thus, the muscle will produce more force for a longer time period if the stimulator is briefly turned off than if the stimuli were allowed to continue without interruption.  Explain why this might occur.
32.   List a few ways that humans could delay the onset of fatigue when they are vigorously using their skeletal muscles.
ACTIVITY 6:  The Skeletal Muscle Length-Tension Relationship
33.   In a force-length graph,
a.   the muscle length is the independent variable.  
b.   the amount of force generated is the dependent variable.
c.   both active and passive forces must be considered.
d.   All the above are correct.
34.   According to your lab manual, the protein titin is the primary cause of _________ __________.
35.   In this lab simulation, the muscle length of _______ mm was able to generate the largest active force.
36.   The force that results from muscles being stretched is called
a.   active force.
b.   passive force.        
c.   maximal tetanic force.
d.   stretch force.
37.   What happens to the amount of total force that the muscle generates during the stimulated twitch?
38.   Based on the unique arrangement of myosin and actin in skeletal muscle sarcomeres, explain why active force varies with changes in the muscle’s resting length.
39.   What range of skeletal muscle lengths generated passive force?  
40.   If you were curling a 7-kg dumbbell, when would your bicep muscles be contracting isometrically?
ACTIVITY 7:  Isotonic Contractions and the Load-Velocity Relationship
41.   The fastest muscle contraction velocity measured in this part of the simulation occurred with the ______ weight.
a.   2.0 gm
b.   1.5 gm          
c.   1.0 gm
d.   0.5 gm
42.   The fastest muscle contraction velocity in this simulation was approximately ________ mm/msec.
43.   True or False:  A muscle that is contracting isometrically will fatigue much slower than one that is contracting isotonically.  
44.   If you were using your biceps muscles to curl a 7kg dumbbell, when would your muscles be contracting isotonically?
45.   Explain why the latent period became longer as the load became heavier in the experiment.
46.   Explain why the shortening velocity became slower as the load became heavier in this experiment.
47.   Explain why it would take you longer to perform 10 repetitions lifting a 10kg weight than it would to perform the same number of repetitions with a 5kg weight.
48.   Describe what would happen in the following experiment:  A 2.5g weight is attached to the end of the isolated whole skeletal muscle used in these experiments.  Simultaneously, the muscle is maximally stimulated by 8.5 volts and the platform supporting the weight is removed.  
a.   Will the muscle generate force?
b.   Will the muscle change length?
c.   What is the name for this type of contraction?

4.Skeletal muscle fibers are usually attached to the skeleton and make voluntary actions such  as walking, talking and standing up possible.

A motor unit consists of a motor neuron and all of the muscle fibers it innervates.

Skeletal Muscle twitch is the mechanical response to a single action potential. It has three   phases known as the latent, contraction, and relaxation phase.

 Electrical stimulus is used to control muscle contractions.

Latent Period is the period of time that elapses between the generation of an action potential in a muscle cell and the start of muscle contraction.

5.Acetylcholine diffuses onto the muscle fiber’s plasma membrane (sarcolemma) and binds to receptors  in the motor end  plate initiating a change in ion permeability that results in a graded depolarization of the muscle plasma membrane (the end plate potential).

6.The events that occur at the neuromuscular junction lead to the end plate potential. The end plate potential triggers a series of events that results in the contraction of a muscle cell. The entire process is called the excitation contraction coupling.

7.The three phases of skeletal muscle twitch are: the latent period, the contraction phase, and the relaxation phase.

The latent phase is the period of time that elapses between the generation of an action potential in a muscle cell and the start of muscle contraction.

The Concentration phases tarts at the end of the latent period and ends when the muscle tension peaks.

The relaxation phase is the period from peak tension until the end of the muscle contraction.

8.No. In all of the tests the latent period remained the same.

9.During the threshold stimulus sodium ions move into the cell.

10. .8 volts, .02grams
11. False
12. Increasing the stimulus voltage on the isolated skeletal muscle mimics how  the nervous system increase the activated number of motor units, thus the total force produced by the muscle increases.
13.The change in the whole muscle force where additional motor units are recruited to increase the total muscle force produced mimicking how the nervous system increases the number of activated motor units.
14. When maximal voltage was applied to the isolated skeletal muscle increased total muscle force, which increased the need for motor units resulting in motor unit recruitment.

16.C. Ca2+
17.Stimulus Intensity means the strength of the force. Stimulus Frequency means the rate of stimulus delivery to the muscle.
18. Treppe. For the first few twitches, each successive twitch produces slightly more force than the previous twitch as long as the muscle is allowed to fully relax between stimuli and the stimuli are delivered relatively close together.
19. Wave Summation. This is when a skeletal muscle is stimulated repeatly, which results in strong muscular contraction than a stand-alone twitch.
20. No, I did not have to increase the stimulus voltage above 8.5 volts. In order to achieve an active force of 5.2g the stimuli needed to be delivered in rapid succession in a short amount of time and not allowing for full relaxation of the muscle. In order to get 5.2g of active force, wave summation needed to be performed.

21.Unfused Tetanus
22.C. To prevent the development of a condition called “lock jaw” that can develop from a specific bacterial infection.
24.When the stimulus frequency was at the lowest, (50s/s) the force was at its lowest level out of all of the experiments. As the stimulus frequency was increased to 130, s/s the force increased slightly but fused tetanus developed at the higher frequency. When the stimulus frequency was increased to the amounts of 146-150 s/s, the force reached a plateau and maximal tetanic tension occurred, where no further increases in force occur from additional stimulus frequency.  
25. At 50- Unfused Tetanus
At 140- Fused Tetanus
At 146 and above-  Maximal Tetanic Tension
26.Maximal Tetanic Tension

28.B. The development of fatigue will be delayed.
29.The contractile force over time
30.It is suspected that fatigue is caused by an a accumulation of lactic acid, ADP, and P, in muscles. Another reason  comes from Calcium levels decreasing from muscle contractions.
31.By turning the stimulator off, a period of rest is created; thus allowing the concentrations of intercellular concentrations of Lactic Acid, ADP, and Pi to decrease. With these concentrations being at a decreased level, the length of time that the muscle is able to maintain maximum tension increases. If the stimulator was not turned off for a short time, the muscle would not be allowed to reach a rest period and further fatigue would continue.
32.In exercising people could delay the onset of fatigue by:
-Doing multiple sets of low repetition exercise
-Allowing for multiple times of rest periods
Healthy Diet, along with adequate exercise. (Frequent exercise creates endurance, and endurance resists fatigue.)
ACTIVITY 6:  The Skeletal Muscle Length-Tension Relationship
33.D. All of the above correct
34.Passive Force
35.75mm – Active force of 1.82
36.B. Passive Force
37.Total force is altered by the starting resting length. My prediction was correct in that it would change either way, with either lengthening the muscle or shortening it, both methods changed the total force generated by the muscle. If the muscle is lengthened the passive force increases, and if the muscle is shortened the active force increases. With each force (a&p) the total force is changed depending on the amount of either A or P forces.
38.Active force generates from myosin thick filaments bind to thin actin filaments, engaging the cross bridge cycle and ATP hydrolysis. Active force data changes as the resting length of the muscle changes. When the resting length of the muscle shortens, the active force amount increases. When the resting length of the muscle is lengthened, the active force amount decreases. The change in the active force amount is completely caused by the amount of myosis bound to actin. The shorter the muscle’s resting length is, the more myosis filaments bind to actin filaments.
39.80, 90, and 100
40.At any point in which the bicep muscle remains at a fixed length.
41.D. 0.5 gm
44.When your arm extends downwards to the point of it being straight. (but not while it is straight) & when the arm rises from the down position back to the raised position.
45.The latent period occurs when there is a rise in muscle tension but no movement or contraction of the muscle. Cross bridges cycle and when the muscle tension exceeds the load, muscle shortening happens. The latent period increases as the weight of the load gets heavier, this is for the necessary force to be generated by the muscle.
46.The shortening velocity refers to the speed of the contraction from the muscle shortening while lifting a load. Maximal shortening velocity is only attained with a minimal load. With a light load, the shortening velocity is at its Maximal shortening velocity. When the weight is heavy, the speed in which the muscle lifts the weight decreases in speed at a slower velocity.
47.It would take longer with the heavier weight because as the weight of the load increases, so does the latent period time and the shortening velocity speeds. With the lighter weight, the muscle is contracted quicker in both latent and shortening velocity speeds.
48. A. The muscle generates force in terms of passive force in where the muscle does react to the electrical stimulus but the weight of the load pulling downwards would not allow the muscle to visibly move. The force is generated from stretching the muscle caused by the recoil of the tissue.
B. If the platform that supports the weight is removed, and the 2.5g weight is still connected, the weight would pull the muscle downwards causing it to lengthen. The muscle changing length would not be from the result of muscle contractions, but only from the weight pulling down.
C. This type of contraction would be Isometric
5 years ago
2.Define the absolute refractory period

the absolute refractory period is the interval during which a second action potential absolutely cannot be initiated , no matter how large the stimulus is applied.
5 years ago
These are the answers to PhysioEx 9.0 Exercise 3: Neurophysiology of Nerve Impulses.  I posted this so that you can have a guide to follow along with your lab. I got 100%...hope this helps  Grinning Face
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5 years ago
Thank you for posting this attachment. It helps out a great deal!
5 years ago
Thanks, this is very helpful.
4 years ago
Hey everyone! This is my first time posting... I need a "meaningful" post to view something... so I'm just going to attach PDF files of a bunch of the labs that I've done:

Here are PDF files of PhysioEx 9.0 Exercise 10 Activity 1 - 4
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4 years ago
Thank you! This has been very helpful!
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