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Cardiac muscle |
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This type of muscle tissue is found only in the heart. The heart must beat from the end of the third week of embryonic development, right through until the time we die. If individual cardiac muscle cells are removed from the heart and kept alive in a glass culture dish containing a suitable nutrient medium, they continue to contract rhythmically. Like skeletal muscle cells, cardiac muscle cells have a striated appearance, but unlike skeletal muscle cells they have a branching structure. However, in the living person the intrinsic rhythm of the individual cardiac cells is over-ridden by the nerve supply to the heart. In this way, the rate of contraction of the heart is adjusted to match the needs of the person - whether asleep or dashing for a bus. Most of us cannot consciously change the rate of our heart beat (although some individuals have been able to train themselves to achieve this), so we say that cardiac muscle is under involuntary control. |
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