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Physiolab 9.0 Exercise 2 answers!
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StudleyMcgee
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Activity 1

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. Correct answer
d.   variable, depending on the voltage that was applied to it.   

2.   True or False:  Another name for a muscle cell is “myofibril.”      False-Skeletal Muscles are composed of muscle fibers.

3.   The largest active force that could be generated in the muscle is Activity 1 was _______ grams.   1.82 grams

4.   Define the terms skeletal muscle fiber, motor unit, skeletal muscle twitch, electrical stimulus, and latent period.   Skeletal Muscle Fiber: Skeletal muscle cells that are composed of hundreds to thousands of individual cells that produce muscle tension. These fibers are what move our bodies and generate muscle tension/force that enables us to have manual dexterity.
Motor unit: consists of one motor neuron  and all of the skeletal muscle fibers that it stimulates. The unit is located at the neuromusclular junction, where the axon terminal of the neuron meets, also called the motor end plate.
Skeletal Muscle Twitch: A period of excitation-contraction in which electrical pulses trigger action potentials, The twitch is the result of a mechanical response to a single action potential.
Electrical Stimulus: An isolated stimulus that sends energy through a muscle in which a response occurs. The stimulus generates movement in the muscle and causes the muscle to generate contractions.
Latent Period: The beginning stage of muscle contractions. This stage produces no muscle force, but prepares the cells for oncoming contractions by releasing chemicals to the cells.

5.   What is the role of acetylcholine (ACh) in a skeletal muscle contraction?   ACH is released at the end-plate potential. ACH diffuses into the sarcolemma, attaches to the receptors in the motor end plate and causes a change in the ions permeability that creates graded depolarization of the end-plate potential. Basically, it attaches to the receptors in the motor-end plate and creates the beginning process of triggering muscle contractions.

6.   Describe the process of excitation-contraction coupling in skeletal muscle fibers.   The motor unit meets at the neuromusclular junction, where the axon terminal of a neuron and muscle fiber’s plasma membrane meet, also called the motor end plate. What occurs in this area lead to the end-plate potential, where an action potential in motor neurons causes the release of ACH. The ACH diffuses into the muscle fiber membrane and changes the ions permeability that creates graded depolarization of the end-plate potential. The end-plate potential triggers events that create contraction of the muscle cell. This entire process of events makes up what is known as excitation-contraction coupling in the skeletal muscle fibers. 

7.   Describe the three phases of a skeletal muscle twitch.   Latent Phase: During this phase there is no muscle contraction. This phase is the period of time prior to muscle contractions. The latent phase, chemical changes in the cells occur in preparation for muscle contractions.
Contraction Phase: Is the period in which the muscle tension is at it’s highest. This is the time where the greatest amount of muscle force is generated.  It begins at the end of the latent period and ends when tension peaks at it’s highest.
Relaxation Phase: The period of contraction after the contraction phase, and ends at end of muscle contraction. 

8.   Does the duration of the latent period change with different stimulus voltages?   No. In all tests, the latent period remained the same.

9.   At the threshold stimulus, do sodium ions start to move into or out of the cell to bring about the membrane depolarization?   The threshold is the time at which the sodium ions start moving into 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.   0.8 Volts
0.02 Grams of active force

11.   True or False:  In a resting skeletal muscle cell, most of the calcium ions freely move through the cytoplasm of the cell.      False

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?   As the stimulus voltage is increased past the muscle’s threshold voltage, the amount of force in the entire muscle increases. Each time the voltage was increased the force generated from the muscle also increased. This occurs because as the voltage increases, and is delivered to the whole muscle, more fibers are activated and causes total force produced by the muscles to increase.

13.   How is this change in whole-muscle force achieved in vivo (eg. in the human body)?   The increase of electrical current causes a progressive increase in the amount of muscle force based on the amount of the electrical current. At the beginning stage, the electric current must surpass the threshold voltage. Once the stimulus voltage goes beyond the threshold it creates whole muscle force. Increasingly the force gets stronger with the higher stimulus voltage until it plateaus at Maximal tension. The Maximal tension has a maximum amount of voltage that it will achieve to increase the force, but only to a maximum point. Whole-Muscle Force is achieved in Vivo by recruitment of additional motor units that increase the total muscle force produced.

14.   What happened in the isolated skeletal muscle when the maximal voltage was applied?   All of the muscle fibers in the isolated skeletal muscle became depolarized and all developed active force. So each of the fibers were involved in the active force generated from the maximal voltage. 

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.   False

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+ This is the correct answer
d.   ADP   

17.   What is the difference between stimulus intensity and stimulus frequency?   Stimulus intensity describes the amount of force generated to administer the stimulus. For example; if a person was being hit in the arm the intensity would be how hard the other person’s fist was hitting their arm. The more force that is used will increase the stimulus intensity. Stimulus frequency refers to the rate of delivered stimulus to the muscle.  In other words, the measured frequency and amount of stimulus to a muscle that occur[(s) (ed)] in a given amount of time.

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?   When stimulating the isolated skeletal muscle multiple times in a short period with complete relaxation between each stimuli the amount of force between each stimulus increased progressively in step like form to a maximum peak in which a plateau of the force occurred. This is known as Treppe. 

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?   When the stimulation frequency was increased to the point in which muscle relaxation did not occur the amount of force progressively increased with each stimulus.  When muscle twitches overlap, no muscles relax, and stimuli occurs one after another in a short amount of time, the muscle contraction is higher than if a single stand alone contraction had occurred. This is known as 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?   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.

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.   Unfused Tetanus

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.-this is the correct answer
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.   5.95 Grams

24.   Describe how increasing the stimulus frequency affected the force developed by the isolated whole skeletal muscle in this activity.   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.   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.   50- Unfused Tetanus
140-Fused Tetanus
146+ Maximal Tetanic Tension

26.   Beyond what stimulus frequency is there no further increase in the peak force?  What is the muscle tension called at this frequency?   Maximal Tetanic Tension

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.   False

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.-correct answer      
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?     When a skeletal muscle fatigues the contractile force declines due to previous contractile activity. Once the muscle has reached maximum tetanic tension, there is no longer an increase in force generated by the muscle. At this stage, the muscle becomes fatigued and contractile force starts to decrease over time.

30.   What are some proposed causes of skeletal muscle fatigue?   The buildup of lactic acid, ADP, and Pi in the muscle fibers. One other reason comes from Calcium levels decreasing from muscle contractions.

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.    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.   List a few ways that humans could delay the onset of fatigue when they are vigorously using their skeletal muscles.   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.   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.   correct answer

34.   According to your lab manual, the protein titin is the primary cause of _________ __________.   Passive Force

35.   In this lab simulation, the muscle length of _______ mm was able to generate the largest active force.   75mm – Active force of 1.82

36.   The force that results from muscles being stretched is called
a.   active force.
b.   passive force.   correct anwer      
c.   maximal tetanic force.
d.   stretch force.   

37.   What happens to the amount of total force that the muscle generates during the stimulated twitch?   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.   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.   Active force is generated 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 is shortened, 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.   What range of skeletal muscle lengths generated passive force?     80, 90, and 100

40.   If you were curling a 7-kg dumbbell, when would your bicep muscles be contracting isometrically?   At any point in which the bicep muscle remains at a fixed length. My best example is holding 2 dumbbells parallel to the floor and holding them in that position for 30 seconds. The muscles are contracting but are not shortening.

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   correct answer

42.   The fastest muscle contraction velocity in this simulation was approximately ________ mm/msec.   0.100

43.   True or False:  A muscle that is contracting isometrically will fatigue much slower than one that is contracting isotonically.     True

44.   If you were using your biceps muscles to curl a 7kg dumbbell, when would your muscles be contracting isotonically?   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.   Explain why the latent period became longer as the load became heavier in the experiment.   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.   Explain why the shortening velocity became slower as the load became heavier in this experiment.   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.   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.   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.   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?   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

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Reply# 1
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3 years ago

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The first three are

D

True

1.82



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3 years ago

Rest of Activity 1

1.   Define the terms skeletal muscle fiber, motor unit, skeletal muscle twitch, electrical stimulus, and latent period.   Skeletal muscle fiber:  voluntary muscle made up of muscle fibers
Motor unit:  consists of motor neuron and all of the muscle fibers it innervates
Skeletal muscle twitch: mechanical response to a single action potential
Electrical stimulus: electrical stimulants
Latent period: period of time that elapses between the generation of an action potential in a muscle cell and the start of muscle contraction
2.   What is the role of acetylcholine (ACh) in a skeletal muscle contraction?   Diffuses on the muscle fibers plasma membrane
3.   Describe the process of excitation-contraction coupling in skeletal muscle fibers.   Motor neuron triggers the release of acetylcholine. Acetylcholine diffuses on the muscle fiber’s plasma and binds the motor end plate that results in graded depolarization.  The events lead to the end-plate potential.  This then triggers a series of events that results in the contraction of a muscle cell.
4.   Describe the three phases of a skeletal muscle twitch.   Latent period, contraction phase, relaxation phase
5.   Does the duration of the latent period change with different stimulus voltages?   Yes
6.   At the threshold stimulus, do sodium ions start to move into or out of the cell to bring about the membrane depolarization?   Yes



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Reply# 3
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3 years ago

YES!!  THANK YOU SOOOO MUCH!  NICE WORK!



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Reply# 4
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3 years ago

thank you sooooo muchhhhhhh. nice job.  Congratulations Kiss



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Reply# 5
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3 years ago

The first three are

D

True ---> ITS FALSE! Number 2 is False, I just got mine returned by the teacher.

1.82

Also Number 43 is FALSE as well, she just corrected mine



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Reply# 6
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3 years ago

thank you  Grin



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Reply# 7
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3 years ago

Thanks, I also had # 43 wrong. I am just trying to verify my answers as well.



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Reply# 8
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A year ago

Thank you, you have no idea how much this has helped me, i ham having the hardest time understanding this.



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Reply# 9
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A year ago

This was so helpful! I have found it a great starting place to check my understanding in doing these labs. Being a new bio student I feel really unsure of my answers! These help to reaffirm that I sort of know what I am doing. Thanks!



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