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Glycerinated Muscle Activity

You have probably found that most students learn about the structure of muscle and the mechanism of muscle contraction far more easily if they are able to visualize and manipulate the structures being discussed. Charts and models are good for visualizing muscle placement on the body, but the realistic look and operation of the muscles are lost. Preserved specimens Glycerinated muscle are good for visualizing also, but the contraction of the muscle still cannot be seen. Carolina's ATP Muscle Kit allows students not only to observe muscle structure but also to experiment with different solutions that make the muscle contract. They can hypothesize about the outcome and actually witness the graded muscle contractions on a microscope slide.

Muscle physiology

Muscle is composed of bundles of fibers, which in turn are composed of smaller structures, myofibrils. Myofibrils make up about 75% of a muscle's total volume, and it is these structures that are ultimately responsible for the observed muscle contraction.

Under a microscope, a muscle's myofibrils appear striated because of the repeating pattern of bands perpendicular to the length of the muscle. This banded pattern is caused by an organized, parallel arrangement of the 2 types of protein filaments in a myofibril. The thicker filaments—composed of myosin—and the thinner filaments—composed of actin—overlap in ordered, repeating units called sarcomeres that can be seen as alternating bands under a microscope.

When a muscle contracts, the myosin filaments bind to the actin filaments, causing them to be pulled inwards and causing the overall width of the sarcomeres to become narrower. For this contraction to take place, ATP must first activate the myosin filaments.

The activity

This activity is designed for minimal prep time and can be completed in one class period. Students can see muscle response without the aid of a microscope, but low magnification is suggested for the observation of muscle structure. Using a microscope or hand lens, students are able to observe the banded pattern, or striations, of the muscle. These striations correspond to the different segments of the sarcomeres, which make the framework of myofibrils. This activity allows you to introduce topics such as muscle development and how a muscle's form fits its function.

Chemicals

Suggested for the observation of muscle structure. Using a microscope or hand lens, students are able to observe the banded pattern, or striations, of the muscle. These striations correspond to the different segments of the sarcomeres, which make the framework of myofibrils. This activity allows you to introduce topics such as muscle development and how a muscle's form fits its function.

The activity also gives you a great opportunity to introduce the requirements needed by a muscle to contract, and to distinguish how these requirements differ between living and glycerinated muscle tissues. Unlike living muscle, glycerinated muscle does not require the presence of Ca2+ to contract. The glycerination process disrupts a regulatory mechanism known as the troponin/tropomyosin complex, and with it the need for Ca2+. ATP, however, is still needed to induce contraction.

Students apply 3 different ATP and ion solutions to the glycerinated muscle and observe the effects. They measure the pre- and postcontraction width of the sarcomeres and identify the solution that causes the highest degree of contraction. Under favorable conditions, the muscles contract to almost 50% of their starting length within only 10 seconds. If students observe the muscle under magnification, it may even contract right out of their field of view! Postcontraction striations are still visible under low magnification.

Carolina's ATP Muscle Kit

Carolina's redesigned ATP Muscle Kit makes it fast and easy for a class of 32 students to learn hands-on about muscle structure and physiology. It comes with background information, illustrations, and student protocols for completing the exercise. Magnifying glasses, microscope slides, and coverslips have also been added for a more complete kit. All that is needed in addition to the kit are scissors, teasing needles, and millimeter rulers. A dissecting microscope is optional. This kit is designed for students in grade 9 to college and meets the following National Science Education Standards for content:

  • Grades 9-12, Life Science—Matter, Energy, and Organization in Living Systems
  • Grades 9-12, Science As Inquiry—Abilities Necessary to Do Scientific Inquiry; Understanding about Scientific Inquiry
  • Grades 9-12, Unifying Concepts and Processes—Change, Constancy, and Measurement; Form and Function
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