Muscle: Cell Junctions
There are several kinds of cell-cell junctions. A description of these can be found here.
Cardiac cells are special, amongst the muscle types, because they are connected to each other by intercalated discs - structures that are only found in cardiac muscle cells. These can be seen in this diagram, as darkly staining irregular lines, at 90 degrees to the striped sarcomeric pattern.
Intercalated discs contain three different types of cell-cell junctions:
adherens junctions (anchoring junctions)
- where actin filaments attach thin filaments in the muscle sarcomeres to the cell membrane.
- Expanded desmosomes
- sites of strong adhesion, that help to keep the muscle cells connected when they contract.
- Gap junctions
- large and small, which provide direct contact between the cardiac cells, facilitating electrical communication, so that waves of depolarisation spread rapidly over the entire heart, by passing from cell to cell.
Skeletal muscle does not have any cell-cell junctions.
Smooth muscle contains gap junctions, to allow a rapid spread of depolarisation, as in cardiac muscle.