Muscle Contraction Essay

Skeleton Muscle Lab

Introduction:

The contraction of a muscle is a complex process, requiring several molecules including ATP and Cl-, and certain regulatory mechanisms [1]. Myosin is motor protein that converts chemical bond energy from ATP into mechanical energy of motion [1]. Muscle contraction is also regulated by the amount of action potentials that the muscle receives [2]. A greater number of actions potentials are required to elicit more muscles fibers to contract thus increasing the contraction strength [2]. Studied indicate that the larger motor units, which were recruited at higher threshold forces, tended to have shorter contraction times than the smaller units [3]. The aims of the experiment were to reinforce the concept that many chemicals are required for skeletal muscle contraction to occur by using the rabbit muscle (Lepus curpaeums) [2]. In addition, the experiment was an opportunity to measure the strength of contraction and to observe the number of motor units that need to be recruited to maintain a constant force as the muscles begin to fatigue [2]. Hypothetically, the rabbit muscle fiber should contract most with ATP and salt solution; and the amount of motor units involved would increase with a decreasing level of force applied until fatigue stage is reached.

Materials and Methods:

The experiment that tested the contractile level of muscle in various solutions used a muscle fiber from rabbit’s muscle. One fiber was detached, put under microscope, and submerged first under ATP and salt solution (KCl and MgCl2), then ATP only solution, and lastly salt only solution [2]. The fiber’s level of contraction was measured in micrometers. Muscle contractile strength and number motor units employed at various force lev...

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...gth of contraction: The muscle can be fine or coarse depending on the amount of motor units connected to muscle fibers. For example, the fine muscles contract faster because of higher number of motor units. The length of muscle in terms of its sarcomeres has an effect on the contraction length. The actions potentials have to get farther along and reach more sarcomeres to have them contract (Q3) [1], [2].

Referenced:

[1] Freeman, S. 2013 Biological Science, 5th ed. Pp 973-976

[2] Zelick, R. 2014. Muscle Lab Exercise. Bi253 Lab Manual. Portland State University, OR, pp. 1-5

[3] H. S. Milner-Brown, R. B. Stein, and R. Yemm. "The Orderly Recruitment of Human Motor Units during Voluntary Isometric Contractions." The Physiological Society 230th ser. (1973): 359-70. Web. 22 May 2014.

[4] Nicholas, M. 2014 .Muscle Lab PowerPoint. Bi253 Lab. Portland State University, OR