CH 9Cardiac

Muscle

Histology

J.F. Thompson, Ph.D.

The MyocardiumForms most of the heart wall (myocardium)

Cardiac Muscle

• Individual uninucleate cells (may occasionally be binucleate)– Not dividing

• Rich capillary blood supply

Cardiac Muscle• Striated

• Cells may be branched

Cardiac Muscle• Involuntary (unconscious)

• Autorhythmicity (contracts without external stimuli)

• Rapid contracting and relaxing

• Non-fatigable

Cardiac Muscle Cells• Each fiber is connected to the others by intercalated discs

IntercalatedDiscs

• Tight Junctions• Desmosomes

– connect cells

• Gap junctions – Electrical synapses

– Excitation spreads rapidly

Cardiac Muscle

Note the striations which represent myofibrils and the sliding filament method of muscle contraction.

End CH 9

Cardiac Muscle Histology