frog_muscle.jpg
frog_muscle.jpg

Comparative Physiology


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Comparative Physiology


Teaching

I derive a great deal of personal satisfaction from teaching.  So much so that I have occasionally been guilty of neglecting my research duties while working on new material for my classes.  I have taught a pretty diverse set of biology lab courses, including mammalogy, comparative vertebrate anatomy, and human anatomy and physiology.  The course that I have the most experience with, though, is comparative and environmental physiology.  I have also guest lectured in the lecture portion of most of these courses.  I will use this portion of my website to share some of my teaching experiences, and some of the interesting material that we have covered. 

The aquatic frog  Xenopus laevis .  Via  Wikipedia Commons .

The aquatic frog Xenopus laevis.  Via Wikipedia Commons.

I'll begin with the banner image for this section.  What you are looking at is a thin cross section of the gastrocnemius (the calf muscle) from an aquatic frog (Xenopus laevis).  The purple-ish round things that look like translucent grains of sand are individual muscle fibers that have been stained with a compound that reacts with one of the key enzymes in the citric acid cycle.  Essentially, the depth of the purple color increases with the aerobic capacity of the fiber.  Keen observers will notice that the fibers in this image fall into three general color classes: dark, light, and intermediate.  If you look closer, you'll also notice that each of those color classes also tends to have its own characteristic size.  Dark fibers tend to be smaller than the others, the light fibers are the largest, and the intermediate colored fibers are, well, intermediate in size, too.  It turns out that each of these three color and size classes corresponds with one of the three primary types of vertebrate muscle fibers.  The small dark fibers are slow oxidative fibers (also called slow-twitch fibers) that don't produce huge amounts of force, but they are incredibly resistant to fatigue.  The large, light colored fibers are fast glycolytic fibers (also called fast-twitch), which can produce large amounts of force, but over relatively short periods of time.  The intermediate fibers are a super cool fiber type called fast oxidative-glycolytic (FOG) fibers, which sort of combine the best of both worlds.  They are capable of producing fairly large amounts of force, but are also pretty resistant to fatigue.  They're ideal for long distance, power-demanding activities... like flight.  Unsurprisingly, FOG fibers are found at pretty high densities in the flight muscles of birds.  And, apparently, occasionally in the leg muscles of aquatic frogs.

Thin section of gastrocnemius muscle from Xenopus laevis. The preparation was done by students in my comparative physiology lab at  UNC Chapel Hill .

Thin section of gastrocnemius muscle from Xenopus laevis. The preparation was done by students in my comparative physiology lab at UNC Chapel Hill.