A biopsy was taken from a leg muscle of a healthy racehorse. The muscle fibres were teased apart and cross-sections were taken from one of the muscle fibres. These cross-sections were examined with a transmission electron microscope. The figure shows drawings made from three different cross-sections of a myofibril from the muscle fibre.

a. Explain the differences between the sections X, Y and Z. You may draw a labelled diagram to illustrate your answer.

b. The sections were taken from a relaxed muscle fibre. Suggest how the sections would appear if taken from a fibre that had contracted to its maximum extent. Explain your answer.

c. Muscle weakness in racehorses may sometimes be related to a deficiency of calcium. Outline the roles of calcium ions in the coordination of muscle contraction.

Transcribed Image Text:

X Y