Library · Histology
Myocardium
Make it clearer
The heart wall has three layers, and the middle one, the myocardium, is a large part of that wall.
Its cells are called cardiomyocytes. Under the microscope they have striations, like the muscle of an arm, but they differ in three ways: they are branched rather than straight, they almost always have a single nucleus, and they connect to one another through structures called intercalated discs.
That disc is not just glue. It holds two things. Gap junctions are passageways that let the electrical signal run straight from one cell to the next, so that the impulse spreads cell by cell, in a coordinated way, through the whole tissue. It is a power grid of connected houses: when one lights up, the next one lights up on its own. Desmosomes are the anchors that keep the cells from pulling apart with the tug of every beat.
There is a hard limit: these cells do not regenerate. That is why, after a heart attack, the area that died does not become muscle again; it becomes scar tissue.
In brief
The heart wall has three layers; the myocardium is the middle one and a large part of that wall.
It is built from cardiomyocytes, striated but branched, almost always with a single nucleus, joined to one another by intercalated discs.
Those discs contain gap junctions that spread the impulse and desmosomes that anchor the fibers.
A power grid of connected houses: when one lights up, the next one lights up on its own.
Cardiomyocytes do not regenerate: after a heart attack, the necrotic area is replaced by scar tissue.
Sources (2)
- National Center for Biotechnology Information, StatPearls PublishingHistology, Heart, StatPearlsPublished
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Cardiac Muscle, StatPearlsPublished
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