Cardiac Muscle

Cardiac muscle resembles skeletal muscle in the striations and thus also known as striated muscles.  However, cardiac muscle is different in that cardiac muscle cells (cardiacmyocytes) do not fuse and thus the resulting fibers are not multinucleated.  Each cardiacmyocyte are however connected to one another via intercalated discs (a specialized junction) which allow for coordinated contraction.  These intercalated discs show up as lines that are particularly thick in comparison to the striations.  Notice also that each cell could branch off.

Another distinction in comparison to skeletal muscle is that these are involuntary muscles.

Whole Rat Heart, l.s.jpg
Whole rat heart, l.s.  Notice the thicker wall of the left ventricle in comparison to the thinner right ventricle.  (TM: ~2.5x, picture taken with a Nikon Coolscan V slide scanner)
Cardiac muscle.  Notice the striations, intercalated discs that are thicker than striations, and branching of the cells.  (TM: 400x, picture taken with a Zeiss Planapo 40/1.0 Oil on Sony A7ii)
Cardiac muscle.  Same view as above.  Annotated version here.(TM: 630x, picture taken with a Zeiss Planapo 63/1.4 Oil on Sony A7ii)

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