Heart > Cardiac Muscle

The muscle found in the heart is unique though it does have some similarity with other types of muscle.

There are 3 types of muscle tissue:

  • Smooth(called smooth as there are no stripes)
  • Skeletal or striated (has a striped appearance)
  • Cardiac (only found in the heart and has a striped appearance - see diagram below)

Muscle tissue is made of excitable cells that are capable of contraction. Muscle tissue has numerous microfilaments composed of actin and myosin which are contractile proteins.

cardiac muscle

In all three muscle types muscle contraction involves microfilaments sliding over each other making the muscle fibre shorter. This sliding and interaction of actin and myosin filaments is regulated by the concentration of calcium ions, which in turn is controlled by a stimulus acting on the muscle tissue. The stimulus to contract may be neural, hormonal or an inherent property of the muscle tissue itself. The three muscle tissues do differ in structure and the role they perform

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Cardiac muscle

The unique structure of cardiac muscle enables the cells to act as if they were one unit, this is described as a functional syncytium. Muscle proteins and the contraction mechanism are broadly similar to skeletal muscle. The cells of cardiac muscles have one nucleus, are short and branched. The cells appear striped due to the order of filaments within them.

The interconnections between cells are called intercalated discs. At an intercalated disc the cell membranes of two adjacent cardiac muscle cells are extensively intertwined and bound together by gap junctions and desmosomes. Desmosomes hold the cells tightly together so they don’t separate during contraction.

The gap junctions allow ions and small molecules to move from one cell to another. This arrangement creates a direct electrical connection between the two muscle cells and allows electrical activity to pass easily between the cells. An action potential can travel across an intercalated disc, moving quickly from one cardiac muscle cell to another.

Cardiac muscle cells contain many more mitochondria than skeletal muscle cells in order to generate the energy needed to power contraction. Cardiac muscle is said to be involuntary as you can’t voluntarily cause it to contract which you can with skeletal muscle.


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