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Lesson: Chapter 1 — Living Tissues

1.2.3. Muscle tissue 4 of 6

Cardiac muscle

A tissue that has contracted about once a second since before you were born, and has never once needed a rest.

Figure to be added

Figure 1.20 — cardiac muscle tissue: striated fibres that branch and rejoin to form a network, each with a single nucleus, and dark bands called intercalated discs marking the boundaries where one cell meets the next.

Where it is found

Cardiac muscle tissue is made of cardiac muscle cells, and it can be described as a special tissue seen only in the heart. Nowhere else in the body has it.

The characteristics

  • Cardiac muscle cells are uninucleate cells bearing cross striations, and they are branched.
  • They never tire, from birth until death, and they act rhythmically.
  • Intercalated discs are situated between the cells, and the tissue acts involuntarily.

Branching is what makes a heartbeat one beat

Because the fibres branch and join, cardiac muscle is a connected network rather than a bundle of separate strands. A signal entering anywhere spreads through the whole sheet, so the muscle contracts as one unit instead of fibre by fibre. The intercalated discs are the junctions that let the signal cross from cell to cell.