Cardiac Muscle
Cardiac muscle is found only in the heart. Its mechanisms of contraction is similar to skeletal and smooth muscle, but with some differences.
Cardiac muscle is composed of branching, striated, and interconnected cells in a three-dimensional network.
1. Myosin and actin is organized similar to skeletal muscle.
2. Cardiac muscle also has many mitochondria, transverse tubules, and sarcoplasmic reticulum.
Differences Between Cardiac and Skeletal Muscle
1. Cisternae of cardiac muscle fibers are less well-developed and store less calcium than skeletal muscles.
2. Transverse tubules in cardiac muscle are larger and release more calcium ions in the sarcoplasmic in response to stimulation.
3. The extra calcium from the transverse tubules also comes from the extracellular fluid. The extra calcium causes cardiac muscle twitches to be longer than skeletal muscle twitches.
4. Intercalated discs – At the end of cardiac muscle cells are intercalated discs that allow muscle impulses to pass freely from one fiber to the next. They rapidly pass signals from cell to cell. The intercalated discs help transmit the force of contraction from cell to cell along with signals, which allows cardiac muscle to contract as a functional unit.
Cardiac muscle is also rhythmic and self exciting. Rhythmic refers to the consistent contraction rate. Self exciting is the ability of cardiac muscle to produce its own contraction signal. Cardiac muscle sets its own rate of contraction which can be modified by signals from the nervous system and with specific hormones.