ACTIVITY 9 : HISTOLOGY cardiac muscle/ LM: high magnification

Cardiac muscle fiber image (green highlight)

Intercalated disc image (green highlight)

Cardiac muscle fiber

Location:

• Myocardium (muscular walls of heart)

• Walls of pulmonary veins and superior vena cava

Description:

• Short, branched muscle fibers joined end-to-end by intercalated discs

• Striated, involuntary muscle

• Contains one or two centrally placed nuclei

• Perinuclear cytoplasm apparent

Function:

• Involuntary contraction of myocardium

• Contraction may be modulated by autonomic nervous system

Comment:

• Intercalated discs contain numerous desmosomes and gap junctions

• Cardiac muscle fiber also known as cardiac muscle cell or cardiomyocyte

Intercalated disc

Location:

• Between cardiac muscle fibers

Description:

• Interdigitating folds of cell membrane that are sites of adhering (mechanical) junctions and gap (electrical) junctions

Function:

• Mechanical connection between adjacent cardiac muscle cells

• Electrical connection between adjacent cardiac muscle cells, providing for spread of polarization impulses throughout myocardium

Comment:

• Adhering junctions also known as desmosomes

• Cardiac muscle fiber also known as cardiac muscle cell or cardiomyocyte