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Biology-Related Homework Help Anatomy and Physiology Topic started by: Jaykob101409 on Nov 17, 2011



Title: Some answers to PhysioEX 9.0 Exercise 2
Post by: Jaykob101409 on Nov 17, 2011
4. Define the terms skeletal muscle fiber, motor unit, skeletal muscle twitch, electrical stimulus, and latent period. Skeletal muscle fiber: The name for an individual skeletal muscle cell
Motor unit: A motor neuron and all of the muscle fibers that it innervates.

Skeletal muscle twitch: The mechanical response (contraction) to a single action potential.

Electrical stimulus: In this simulation, represents the means of stimulating the muscle. Represents the action potential coming from the motor neuron.

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

6. Describe the process of excitation-contraction coupling in skeletal muscle fibers. (HINT: Look at page 191 in your text…and describe in detail.) Excitation-Contraction Coupling (Fig. 8.7, page 193)

Release of ACh. The nerve impulse arriving at the axon terminal in the motor neuron triggers the release of Ach. The Ach diffuses across the synapse.
ACh receptors are activated. The binding of ACh opens Na+ ion channels in the motor end plate.
Generation of muscle action potential. The AP results from inflow of Na+ ions. The muscle AP travels along the sarcolemma and through the T tubules.
ACh is broken down by acetylcholinesterase.
Release of Ca2+. Calcium ions are released from the sarcoplasmic reticulum into the sarcoplasm.
Ca2+ binds to troponin molecules in the thin filaments. The troponin changes shape exposing the binding sites for myosin.
Myosin heads bind to actin. In the presence of ATP, the myosin heads swivel and release, pulling the thin filaments toward the center of the sarcomere…the contraction.

13. How is this change in whole-muscle force achieved in vivo (eg. in the human body)?

 In vivo, this process in which the number of contracting motor units is increased is called motor unit recruitment. As more and more motor neurons “fire”, more and more muscle fibers are stimulated.

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

24. Describe how increasing the stimulus frequency affected the force developed by the isolated whole skeletal muscle in this activity.

 Increasing the stimulus frequency caused an increase in the amount of active force generated. The amount of variability also decreased as the frequency increased.

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.

As the length of 75mm, an “ideal” number of thin and thick filaments can overlap, contract, and cause active force. If the muscle is shortened or lengthened, there will be fewer of thin and thick filaments overlapping.

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

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.
Answer A.

Hope this helps someone ;D


Title: Re: Some answers to PhysioEX 9.0 Exercise 2
Post by: GMFarmer on Nov 18, 2011
love you man ;D ;D


Title: Re: Some answers to PhysioEX 9.0 Exercise 2
Post by: kjace99 on Nov 18, 2011
Thanks dude....


Title: Re: Some answers to PhysioEX 9.0 Exercise 2
Post by: Jaykob101409 on Nov 18, 2011
You are welcome, I get help when I need it so I like to help whenever I can  ;D


Title: Re: Some answers to PhysioEX 9.0 Exercise 2
Post by: Johm on Dec 22, 2011
Do you have any other answers?


Title: Re: Some answers to PhysioEX 9.0 Exercise 2
Post by: lausengc on Dec 22, 2011
Which ones do you need help with?  Post the questions and I'll help you with them.


Title: Re: Some answers to PhysioEX 9.0 Exercise 2
Post by: Johm on Dec 22, 2011
All of them :'(


Title: Re: Some answers to PhysioEX 9.0 Exercise 2
Post by: lausengc on Dec 23, 2011
Post the questions because I think some of mine are different.


Title: Re: Some answers to PhysioEX 9.0 Exercise 2
Post by: Rothgar on Jan 9, 2012
Can Some one help me with

5.   What is the role of acetylcholine (ACh) in initiating a skeletal muscle contraction?  (HINT:  Look at page 189 in your text…and describe in detail.)
6.   Describe the process of excitation-contraction coupling in skeletal muscle fibers.  (HINT:  Look at page 191 in your text…and describe in detail.)
7.   Describe the three phases of a skeletal muscle twitch. (HINT:  Look at page 196 in your text…and describe in detail.  Do not just name the three phases!)
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?
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.
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?






Title: Re: Some answers to PhysioEX 9.0 Exercise 2
Post by: biolove on Jan 9, 2012
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?

The active force increased as predicted to the point in which it reached a plateau and was no longer able to increase.


Title: Re: Some answers to PhysioEX 9.0 Exercise 2
Post by: Rey leon on Feb 13, 2012
at threshold stimulus, do sodium ions start to move into or out of the cell bring about the membrane depolarization?