Muscle Contraction Modeling

In Anatomy and Physiology class, we are discussing the Sliding Filament Theory of Muscle Contraction.  I gave short notes yesterday (until I could tell I was sounding like Charlie Brown's teacher... wah wah wah...) on the basics of muscle contraction.  In past years my students have had trouble with the idea that although the muscle shortens during a contraction, the individual thick and thin filaments don't change in length.

One thing I'd tried to combat this misconception was to show animations of the process.  I think this helped for some students, but for others the concept still wasn't clear.  This year I decided that in addition to notes, animations, and reading assignments, we would try a little physical model.

I drew up some images of the thin and thick filaments, laminated them on colored paper, and cut them out.  I have this available on my TPT store if you want to download the images and instructions - click here.

Students worked in groups to place the pieces on top of a white board and label the parts, taking a photo of their work.  They had to take two pictures, one of the contracted muscle fiber and one of the relaxed muscle.    The conversations I overheard while they were working were very meaningful, they were engaged and referring back to their readings and notes when discussing both the placement and labeling, and while answering the questions.

After they completed their work they answered 6 questions, bringing together their understanding from the activity today, their reading assignment, and the notes.

1.      When the muscle is contracting, what changes happen to the A band?  I band?  H zone?

2.      What are the purposes of the M line and Z disc?

3.      This is a very simplified model of the myofilaments.  What detail could we add to make it more accurate?

4.      Is there any situation where the thick and thin filaments no longer overlap?  Is there a situation where the thin and thick filaments are incapable of overlapping anymore?

5.      Describe the total length of the sarcomere as the muscle contracts.  Do the lengths of the individual filaments change?

6.      Thinking about what we discussed in class, how does the contraction happen chemically?  Draw a picture and describe the steps.

Hopefully this will drive home the idea that although the sarcomere shortens, the individual filaments do not change in length.