MCPHERSON, D.R.; SUNY at Geneseo: Temperature Effects on Skeletal Muscle Contraction: an Investigative Lab in Animal Physiology

It is often difficult for students to concretely link macroscopic events (e.g., muscle contraction) to their underlying molecular mechanisms (e.g., enzyme activity). The laboratory exercise presented here uses the effects of temperature on muscle contraction to encourage students to integrate the molecular mechanisms of muscle physiology. Students record the force of isometric twitch contractions in frog gastrocnemius muscle (Rana pipiens) using a standard nerve-muscle preparation. Prior to the actual experiment they develop their own hypotheses about the effects of temperature. Cool temperatures cause slowing of force development and relaxation (which students expect) but increase the peak force of contractions (which students do not expect). Conversely, warm temperatures accelerate force development and relaxation (as expected) but decrease peak force (not expected). Recordings begin at room temperature (to which the frogs are acclimated). The students then make recordings at a range of cool temperatures (5-20 ^oC) and warm temperatures (20-30 ^oC). To explain the unexpected effects of temperature on twitch force, students must analyse and integrate the molecular processes that generate force and promote relaxation and they must consider the relative temperature dependence (Q₁₀) of those reactions. The solution to the puzzle is that the Q₁₀ is greater for relaxation processes than for force-producing processes. Students emerge from this exercise with a deeper understanding of muscle physiology.