Isotonic Contraction and the Effect of Load on Skeletal Muscles Essay Sample

10 October 2017

The occupation of the motor nervous system is to command certain elements in musculuss at the same time to finally bring forth motion. Motion of the organic structure is the consequence of specialised cells straight associated with skeletal musculus. Skeletal musculuss are voluntary musculus and must contract before motion can happen. We know the musculus squad traveling the arm is formed at the biceps and triceps. Bicepss can flex the cubitus. but by itself can non widen the arm. Biceps contract and triceps relax to flex the cubitus. When the cubitus is straightened. the contrary takes topographic point ; the biceps relax and triceps contract.

However. what happens during skeletal musculus contraction? For case. what happens to the musculuss in the leg when one lifts weights? We used two variables. musculus length and opposition ; to research how skeletal musculus velocity and contraction is affected during an isosmotic contraction when these variables are manipulated. We found if opposition is excessively light skeletal musculus contracts with easiness and at a faster rate. However. if the opposition is heavy musculus contraction has a much slower rate. These findings give good penetration into safety safeguards. care. and medical diagnoses’ of our organic structure. For case when raising weights. or finding underlining causes of a bosom status. Introduction

The muscular system has more than 600 musculuss ( cardiac. skeletal and smooth musculus ) throughout the human organic structure. Contraction of these musculuss is generated by specialised musculus cells. Skeletal musculuss are voluntary and travel the organic structure by drawing on the castanetss. for case. when throwing a ball or walking. This involves a series of stairss in which castanetss are moved at the joint by a complex electrochemical and mechanical procedure of contraction and relaxation of skeletal musculuss ( Kendal et al. . 2000 ) . First. skeletal musculus fibres communicate with the nervous system at the neuromuscular junction ( NMJ ) by exciting the sarcolemma. Through a procedure called excitation-contraction yoke where acetylcholine ( ACh ) is released into the synaptic cleft. opening sodium ion channels ( Na+ ) and bring forthing an action potency ( AP ) . The AP causes the sarcoplasmic Reticulum ( SR ) to let go of Ca ions ( Ca2+ ) where cross Bridgess are formed and the musculus contraction rhythm is initiated. During the contraction stage. the skeletal musculus shortens bring forthing tenseness on the terminals of the musculus. Next. the relaxation stage. ACh is broken down by acetylcholinesterase ( AChE ) and the AP is ended. The SR reabsorbs the Ca2+ and with no more cross-bridge interaction. the contraction ends returning the musculus to its resting length ( Martini et al. . 2012 ) .

Muscles experience two basic types of contractions called isometric and isosmotic. Isometric contractions occur when there is a rise in musculus tenseness. but the length of the musculus stays the same. Isotonic contractions occur when tenseness in musculus rises and the length of the musculus alterations. This is normally associated with musculus traveling something that is of a fixed weight. Our intent is to “describe the effects of opposition and get downing length on the initial speed of shortening and detect why musculus force remains changeless during isosmotic shortening” ( Marieb et al. 2009 ) . Our findings will supply improved apprehension of how resting length will ensue in maximal force production in human musculuss ( Marieb et al. 2009 ) . Materials

Materials used in the experiment include:
Data aggregation unit. electrical stimulator. electrodes. force transducer. maulerss. musculus support base. myograph. CRO show. platform height simulator. fake musculus. electromotive force control simulator. and weights ( gms ) : 0. 5-g. 1. 0-g. 1. 5-g. and 2. 0-g.

Experiment 1: We began the experiment by puting a hook through the upper sinew of the musculus linking it to the force transducer. Following. we suspended the musculus in the support base and secured it with a 2nd hook at the lower terminal of the musculus sinew. We set a platform tallness of 75mm. put the electromotive force to 8. 2 Vs and added 0. 5-g weight onto the muscle’s lower sinew. Get downing experiment 1. run 1. we applied a stimulation to the musculus and at the same time observed the musculus action. Data was recorded and a 2nd tally was completed after using a 1. 5-g weight in which the information was besides recorded. After we collected initial informations consequences we continued the experiment for a 3rd and 4th tally utilizing 1. 0-g and 2. 0-g weights. After all four tallies were completed we recorded the informations and plotted the consequences. Experiment 2: First we cleared all pervious informations from experiment 1 in the informations control unit. We attached the 1. 5-g weight to the lower musculus sinew. Put the electromotive force to a upper limit of 8. 2 Vs. Get downing with 60mm length on the height platform we ran through a scope of lengths get downing with 60mm to 90mm in 5-mm increases. Consequences from the seven tallies were recorded in the informations aggregator and we plotted the information for analyses. Consequences

Figure 1 shows a baseline experiment ( run 1 ) and grid that diagrammatically shows the contraction informations for analysis. Time ( in msecs ) is along the horizontal axis and force ( in gm ) is on the perpendicular axis. We applied a 0. 5-g stimulation to the musculus and observed the CRO following produced by the stimulation. We observed the following rise from the surface of the platform. level line for a few seconds. followed by a rapid diminution. The force produced remained changeless and did non alteration during the level line of the tracing.

Table 1 shows informations comparing weight and rate of contraction between run 1 and run 2 ( 1. 5-g weight ) . The 0. 5-g weight resulted in the highest rate of contraction with a speed of 3. 77 mm/sec. The pointer indicates the latent period in which no contractions occur.

Figure 2 shows a grid of the relationship between opposition and the initial speed of shortening. Velocity ( in mm/sec ) is on the horizontal
axis and weight ( in gm ) along the perpendicular axis. We completed the 3rd and 4th tally with 1. 0-g and 2. 0-g weights and plotted the information of tallies 1. 2. 3 and 4. The consequences showed the greater the opposition. the shorter the initial speed of shortening or rate of contraction.

Relationship between get downing length and initial speed of shortening

Before we could get down our current experiment we had to find how a musculus responds to a individual stimulation and when does lengthening happen. We found that a musculus contraction in response to a individual stimulation of equal strength is called a musculus vellication. A complete musculus vellication has three phrases: 1 ) Latent period. during which there are no contractions. 2 ) The contraction period is when skeletal musculus contraction starts. 3 ) During the relaxation period. tenseness is reduced and the musculus returns to normal length ( Marieb et al. 2009 ) . Our consequences of experiment 1 showed a response to a individual stimulation as related to jerk and stages. Furthermore. our research concluded when the burden on a musculus exceeds the tenseness generated. a lengthening contraction occurs. Our experiment had two of import variables. get downing length of the musculus and the opposition applied. As illustrated in table 1 and figure 2. if the object is light it can be lifted rapidly. nevertheless a heavier weight will be lifted with a slower speed ( Marieb et al. 2009 ) .

Our findings in experiment 2 concluded the strength of a musculus contraction can be altered by altering the get downing length of the musculus known as the length-tension relationship. Changeless variables 1. 5-g weight and 8. 2 Vs. with alterations in musculus lengths. Our determination showed at 60 millimeter. the musculus is unstretched and produces a weak contraction because the overlapping thin fibrils interfere and conflict with each other curtailing cross span binding and less tenseness develops ( Kendal et al. . 2000 ) . Muscle length of 75 millimeters. we found the musculus was reasonably stretched bespeaking a moderate imbrication of the thin fibrils relative to the cross Bridgess. Therefore maximal tenseness is developed and musculus contraction occurs ( Martini et al. . 2012 ) .

Last. at 90 mm length. the musculus became over-stretched bespeaking the midst and thin fibrils are overlapping merely somewhat. When over stretched the thin fibrils are pulled about to the terminals of the thick fibrils and really small if any tenseness can develop ( Kendal et al. . 2000 ) . Our end was to look into how alterations in musculus length and opposition affect the velocity of skeletal musculus contraction ( Marieb et al. 2009 ) . We found that when a weight is non excessively heavy the musculus can raise it with a faster speed. For illustration. when working out and finishing bicep coils. a 2 lb weight can be lifted rapidly compared to a 50 lb weight. Besides. in human skeletal musculus pulling seldom occurs but this is really of import when sing bosom musculus in relation to congestive bosom failure.


Kandel. ER. . Schwartz. JH. . and Jessell. TM ( 2000 ) . The Motor Unit and Muscle Action. Principles of Neural Science ( chp. 34. 4th edition. pp. 675-683 ) . New York: McGraw-Hill.

Marieb. E. and Mitchell. S. ( 2009 ) . Investigating the Effect of Load on Skeletal Muscle. Laboratory Manual: Human Anatomy & A ; Physiology. ( Exercise 26. 9th edition. pp. 419-420 ) . New York: Pearson Education Inc.

Martini. F. . Nath. J. and Bartholomew. E. ( 2012 ) . Muscle Tissue. Fundamentalss of Anatomy & A ; Physiology. ( chp. 10. 9th edition. pp. 290-305 ) . New York: Pearson Education Inc.

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