False-colour transmission electron micrograph (TEM) of a cardiac muscle cell, showing granules of animal starch, or glycogen, which appear as small black dots. Glycogen is chemically broken down to glucose, and glucose in turn yields energy to power muscle contraction. Most of this chemistry takes place in mitochondria - the elliptical structures at left and bottom right. The image also shows clearly the long threads of the myofibrils and their alternating light and dark sections. The myofibrils are contractile proteins responsible for the heart's insistent rhythm of contraction. Pink tint. Reference: MICROCOSMOS, figure 2.28, page 29.
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