18.4 Cardiac muscle fibers

Cardiac muscle cells:

striated, short, branched, fat, interconnected

cardiac muscle contain

numerous large mitochondria (25–35% of cell volume) that afford resistance to fatigue

Intercalated discs

connecting junctions between cardiac cells that contain desmosomes and Gap Junctions

Desmosomes

Hold cells together; prevent cells from separating during contractiion

Gap junctions

Allow ions to pass from cell to cell; electricity couples adjacent cells

-allows the heart to be a functional syncytium, a single coordinated unit

Intercellular space between cells has

connective tissue matrix (endomysium)

-connects cardiac muscle to cardiac skeleton, giving cells something to pull against

What is the difference between a cardiac and skeletal muscle?

some cardiac muscle cells are self-excitable

2 kinds of myocytes

-Contractile cells

-Pacemaker cells

Contractile Cells

responsible for contraction

Pacemaker Cells

non-contractile cells that spontaneously depolarize

-initiate depolarization of the entire heart

-do not need nervous system stimulation, skeletal muscle fibers are needed for heart

Contraction of all cardiac myocytes ensures

effective pumping action

-skeletal muscles contrast independently