Skeletal and cardiac muscle are both types of striated muscle. You have been given one type of each sample, but the identifying labels have come off

Question

You know that these muscles have some similarities and some differences in terms of their rate of depolarization, rate of repolarization, and length of action potential. Which of these features would not be useful in identifying the two types of muscle? Which of these features will you use to correctly label the samples? Explain what you would expect to see for skeletal and cardiac muscles for each feature that you use.

What will be an ideal response?

Answer 1

Answer: Skeletal and cardiac muscles have similar rates of depolarization, largely because they both use voltage-gated Na+ channels. As a result, this phase of the action potential would not be useful in identifying them. The duration of depolarization is different between the two: it is much longer for cardiac muscle. This is because cardiac muscle uses voltage-sensitive Ca2+ channels that remain open for longer periods of time. As skeletal muscle does not possess these channels, the cells can repolarize more rapidly. This difference relates to the second difference between the two categories of striated muscle: length of action potential. Because cardiac muscle repolarizes slowly, its action potentials also have a longer duration. By the same token, skeletal muscle has an action potential with shorter duration because it repolarizes rapidly. Thus, by stimulating each sample, recording the action potentials, and comparing the rate of repolarization and duration of the action potential, it will be possible to correctly label the two muscle samples.