Online Lab: Muscle FunctionIn this lab project I will be testing my skeletal muscle contractions through three different experiments: testing my check muscle while grinding my teeth, testing my bicep length

before and during flexing, and testing the circumference of my upper arm before and during clenching my fist. After I determine what happens to my muscles under these three

experiments, I will test the effects cold water and fatigue have on my muscles. This is an important lab because it will show how muscles react differently under stressful situations.

Picture from http://health.howstuffworks.com/muscle4.htm

In the first muscle action procedure I placed my fingers along my jaw in front of my ear and grit my teeth several times. When I grit my teeth I

could feel my muscle popping outward and becoming hard right below and in front of my ear. I believe this muscle is known as the masseter muscle

(superficial and deep) and is used for mastication (chewing cycle).

In the second muscle action procedure I observed the difference in my biceps branchii muscle from when my arm is extended straight to when I bend it bringing my hand up towards my shoulder. For this experiment I used

a tape measurer instead of my other hand because I had no one to take the picture for me. The tape measurer shows the distance before and during the contraction. When I bent my arm, bringing my hand toward my

shoulder, my biceps branchii raised upward and shrunk in length; shortening the previous distance from about 8” to about 5”. My triceps branchii, the antagonist muscle, would extend and lengthen while the prime mover

shortened.

The final muscle action procedure was measuring the circumference of my upper arm before and during the process of clenching my fist. My original reading was 9.75” with a relaxed arm. Once my fist was clenched, my muscle popped up and my reading went to 10.125”. My muscles circumference increased

due to the shortening (contraction) of the sarcomeres.

Effect of Temperature on Muscle ContractionDuring this experiment I compared two tests to one another. The first test was to time myself for

20 seconds and see how many fists I could make; from a completely open hand with my palm facing upward, to a tightly fisted hand. The second test was to submerge my hand in ice cold water for one minute and then repeat the previous test. I did the experiment twice because my first calculations were surprisingly close to one another that I thought I would try leaving my

hand submerged longer on the second test. Surprisingly, my second experiment results came out very close to my first experiment results. The first results were 45 fists at normal temperature and 39 fists at cold temperature. The second experiment I left my hand in the ice water for a minute and a half and the results were 44 fists at normal temperature and 39 fists at cold temperature.

Effect of Temperature on Muscle Contraction

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1. What are the three changes you observed in a muscle while it is working?

I noticed that everything worked fast together; from the front of my arm (extensor carpi group and extensor digitorum), through my wrist and hand (flexor carpi group), and in to my fingers. With my palm faced toward the ceiling, I observed my forearm muscles would pop upward and inward (shrinking) as I clenched my fist, becoming very firm. Also, as my biceps branchii muscle would shrink and become firm as I clenched my fist, my triceps branchii acted as a synergist making the action more effective.

2. What effect did cold temperature have on the action of your hand?

Even though my brain was telling me to make a fist, my hand wasn’t responding as fast cold as it was at normal temperature. It took longer to get my fingers to curl inward and make a complete fist, and it hurt because my fingers felt stiff. Ultimately, my cold hand was having a hard time performing fine motor skills!

3. Line graph of data.

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1. What are the changes you observed in your muscles while they were working?

Just as the previous experiment when my hand was at normal temperature, I noticed that everything worked fast together; from the front of my arm (extensor carpi group and extensor digitorum), through my wrist and hand (flexor carpi group), and in to my fingers. As my muscles contracted, they came inward and upward (shrinking), and became firmer. I didn’t have to think about the next muscle contraction because my hand was working so fast in respond.

2. What effect did fatigue have on the action of your hand muscles?

Every 20 seconds that went by, my hand got more and more tired. Since I did not rest in between trials, the fatigue in my hand muscles made it very difficult to tightly clench my fist, especially on the last couple of 20 second trials. It took longer to get my fingers to curl inward and make a complete and tight fist. Although my fingers did not hurt as much during this experiment as the temperature experiment, my hand was hurting on the backside of my palm and my wrist was sore.

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How Muscles WorkRelaxed

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Pictures & Verbiage from http://health.howstuffworks.com/muscle2.htm

The thick and thin filaments do the actual work of a muscle, and the way they do this is pretty cool. Thick filaments are made of a protein called myosin. At the molecular level, a thick filament is a shaft of myosin molecules arranged in a cylinder. Thin filaments are made of another protein called actin. The thin filaments look like two strands of pearls twisted around each other. During contraction, the myosin thick filaments grab on to the actin thin filaments by forming cross-bridges. The thick filaments pull the thin filaments past them, making the sarcomere shorter. In a muscle fiber, the signal for contraction is synchronized over the entire fiber so that all of the myofibrils that make up the sarcomere shorten simultaneously. There are two structures in the grooves of each thin filament that enable the thin filaments to slide along the thick ones: a long, rod-like protein called tropomyosin and a shorter, bead-like protein complex called troponin. Troponin and tropomyosin are the molecular switches that control the interaction of actin and myosin during contraction.

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Imagine you are on the roof of a building and are pulling a bucket from ground level upward via a rope. First your right hand pulls the rope up a little, then your left hand grabs the rope and pulls. You continue this muscle movement until the bucket has reached its destination. Now lets think

about what your muscles are doing while you’re pulling on the rope.

• Myosin molecules are golf-club shaped. In the previous diagram and for our example, the myosin club-head (along with the cross-bridge it forms) is your arm, and the actin filament is the rope.

• During contraction, the myosin molecule forms a chemical bond with an actin molecule on the thin filament (gripping the rope). This chemical bond is the cross-bridge. For clarity, only one cross-bridge was shown in the previous diagram (focusing on one arm).

• Initially, the cross-bridge is extended (your arm extending) with adenosine diphosphate (ADP) and inorganic phosphate (Pi) attached to the myosin.

• As soon as the cross-bridge is formed, the myosin head bends (your arm shortening), thereby creating force and sliding the actin filament past the myosin (pulling the rope). This process is called the power stroke. During the power stroke, myosin releases the ADP and Pi.

• Once ADP and Pi are released, a molecule of adenosine triphosphate (ATP) binds to the myosin. When the ATP binds, the myosin releases the actin molecule (letting go of the rope).

• When the actin is released, the ATP molecule gets split into ADP and Pi by the myosin. The energy from the ATP resets the myosin head to its original position (re-extending your arm).

• The process is repeated. The actions of the myosin molecules are not synchronized -- at any given moment, some myosins are attaching to the actin filament (gripping the rope), others are creating force (pulling the rope) and others are releasing the actin filament (releasing the rope).

How Muscles Work

Verbiage from http://health.howstuffworks.com/muscle2.htm

ConclusionThis lab experiment brought to my attention the importance the muscular system has on my life and my quality of life. Muscles are a vital component of the human body because they take energy and in return produce motion. Out of the three types of tissue (smooth, cardiac, and skeletal), skeleton muscle is the only type that is voluntary. When you speak you’re using muscles, when you write you’re using muscles, everything you can think of doing in your brain can be produced with the help of muscle functions. If you think about everything you do throughout the day

that uses some sort of muscle function, the list would be endless! From showering, to walking, driving, eating, even going to the bathroom!

Cold Temperature Experiment: While my warm hand was in the ice cold water, conduction was taking place. The heat my body was generating was being transferred to the cold water, and little blood vessels in my hand constricted to retain heat (energy). The restriction of blood flow to my hand is what caused the stiffness and the pale appearance

in my hand. To maintain a warmer core area and homeostasis, the tissue blood vessels constrict to keep the blood away from cold areas; this is common in hypothermia patients. The muscles metabolic activities are slowed down or

inhibited depending on how cold the muscle gets. The nerve impulse slows down at the neuromuscular junction, retarding the impulses to muscle fibers.

Fatigue Experiment: Due to the repetitive and prolonged squeezing of the tennis ball, my hand became very tired; to the point where it was painful towards the last couple of sessions. Once the muscle is depleted of its energy reserves,

fatigue kicks in. The sarcoplasmic reticulum will release the calcium which contracts the muscle fibers, and my motor units were responding to the next process of squeezing with out taking a break to relax. Eventually, I was to

the point were even though I wanted to keep squeezing the tennis ball as fast as I could, muscle fatigue started to set in and I saw a decline in the force output. All muscle contractions are powered by a source of fuel; whether it be

ATP, glycogen, or creatine phosphate. If any of these substrates are depleted it will result in muscle fatigue because the cells due not have the proper energy to function efficiently.

Works Cited

Freudenrich, Ph.D., Craig.  "How Muscles Work."  11 April 2001.  HowStuffWorks.com. 1 April 2008. <http://health.howstuffworks.com/muscle.htm>.

Mader, Sylvia S. Human Biology. New York: The McGraw-Hill Companies, Inc, 2008. Pages 227-245.

"Muscle contraction." Wikipedia, The Free Encyclopedia. 1 Apr 2008, 15:33 UTC. Wikimedia Foundation, Inc. 2 Apr 2008

<http://en.wikipedia.org/w/index.php?title=Muscle_contraction&oldid=204231992>.

"Muscle weakness." Wikipedia, The Free Encyclopedia. 1 Apr 2008, 08:28 UTC. Wikimedia Foundation, Inc. 3 Apr 2008

<http://en.wikipedia.org/w/index.php?title=Muscle_weakness&oldid=205514070>.