Cardiac muscle is striated muscle that is present only in the heart. Cardiac muscle fibers have a single nucleus, are branched, and joined to one another by intercalated discs that contain gap junctions for depolarization between cells and desmosomes to hold the fibers together when the heart contracts. Contraction in each cardiac muscle fiber is triggered by Ca++ ions in a similar manner as skeletal muscle, but here the Ca++ ions come from SR and through voltage-gated calcium channels in the sarcolemma. Pacemaker cells stimulate the spontaneous contraction of cardiac muscle as a functional unit, called a syncytium.
autorhythmicity
heart’s ability to control its own contractions
desmosome
cell structure that anchors the ends of cardiac muscle fibers to allow contraction to occur
intercalated disc
part of the sarcolemma that connects cardiac tissue, and contains gap junctions and desmosomes
1. Cardiac muscles differ from skeletal muscles in that they ________.
A) are striated
B) utilize aerobic metabolism
C) contain myofibrils
D) contain intercalated discs
D
2. If cardiac muscle cells were prevented from undergoing aerobic metabolism, they ultimately would ________.
A) undergo glycolysis
B) synthesize ATP
C) stop contracting
D) start contracting
C
1. What would be the drawback of cardiac contractions being the same duration as skeletal muscle contractions?
An action potential could reach a cardiac muscle cell before it has entered the relaxation phase, resulting in the sustained contractions of tetanus. If this happened, the heart would not beat regularly.
2. How are cardiac muscle cells similar to and different from skeletal muscle cells?
Cardiac and skeletal muscle cells both contain ordered myofibrils and are striated. Cardiac muscle cells are branched and contain intercalated discs, which skeletal muscles do not have.