cardiac muscle

Examples of cardiac muscle in the following topics:

• Types of Muscle Tissue

  • The function of muscles is movement, but the types of movement elicited differ between skeletal, cardiac, and smooth muscle.
  • There are three kinds of muscle tissue: skeletal, smooth, and cardiac.
  • Cardiac muscle is found in the walls of the heart.
  • Although cardiac muscle is involuntary in nature, it is structurally different from smooth muscle.
  • Cardiac muscle is striated, similar to skeletal muscle, but beats involuntarily.

• Microscopic Anatomy

  • Cardiac muscle appears striated due to the presence of sarcomeres, the highly organized basic functional unit of muscle tissue.
  • Cardiac muscle, like skeletal muscle, appears striated due to the organization of muscle tissue into sarcomeres.
  • While similar to skeletal muscle, cardiac muscle is different in a few ways.
  • Cardiac muscles are composed of tubular cardiomyocytes, or, cardiac muscle cells.
  • A sarcomere is the basic unit of muscle tissue in both cardiac and skeletal muscle.

• Mechanism and Contraction Events of Cardiac Muscle Fibers

  • Cardiac muscle fibers undergo coordinated contraction via calcium-induced calcium release, conducted through the intercalated discs.
  • In cardiac, skeletal, and some smooth muscle tissue, contraction occurs through a phenomenon known as excitation contraction coupling (ECC).
  • In cardiac muscle, ECC is dependent on a phenomenon called calcium-induced calcium release (CICR), which involves the influx of calcium ions into the cell triggering further release of ions into the cytoplasm.
  • Similarly to skeletal muscle, the influx of sodium ions causes an initial depolarization, however in cardiac muscle, the influx of calcium ions sustains the depolarization so that it lasts longer.
  • The actual mechanical contraction response in cardiac muscle occurs via the sliding filament model of contraction.

• Characteristics of Muscle Tissue

  • The three types of muscle tissue are skeletal, smooth, and cardiac.
  • Cardiac muscle tissue is found only in the heart where cardiac contractions pump blood throughout the body and maintain blood pressure.
  • Cardiac muscle can be further differentiated from skeletal muscle by the presence of intercalated discs which control the synchronized contraction of cardiac tissues.
  • Cardiac and skeletal muscle are both striated in appearance, while smooth muscle is not.
  • Both cardiac and smooth muscle are involuntary while skeletal muscle is voluntary.

• Muscle Tissues and Nervous Tissues

  • There are three types of muscle in animal bodies: smooth, skeletal, and cardiac.
  • Smooth muscle tissue is also called non-striated as it lacks the banded appearance of skeletal and cardiac muscle .
  • Cardiac muscle is found only in the heart.
  • An added feature to cardiac muscle cells is a line that extends along the end of the cell as it abuts the next cardiac cell in the row.
  • Cardiac muscle tissue also has intercalated discs, specialized regions running along the plasma membrane that join adjacent cardiac muscle cells and assist in passing an electrical impulse from cell to cell.

• Structure and Function of the Muscular System

  • Cardiac muscle tissue is found only in the heart, where cardiac contractions pump blood throughout the body and maintain blood pressure.
  • As with skeletal muscle, cardiac muscle is striated; however it is not consciously controlled and so is classified as involuntary.
  • Cardiac muscle can be further differentiated from skeletal muscle by the presence of intercalated discs that control the synchronized contraction of cardiac tissues.
  • The body contains three types of muscle tissue: skeletal muscle, smooth muscle, and cardiac muscle, visualized here using light microscopy.
  • Visible striations in skeletal and cardiac muscle are visible, differentiating them from the more randomised appearance of smooth muscle.

• Myocardial Thickness and Function

  • The myocardium (cardiac muscle), is the thickest section of the heart wall and contains cardiomyocytes, the contractile cell of the heart.
  • The structure of cardiac muscle shares some characteristics with skeletal muscle, but has many unique features of its own.
  • Cardiac muscle, like skeletal muscle, is comprised of sarcomeres, the basic, contractile units of muscle.
  • Cardiac muscle (as well as skeletal muscle) also contain the protein myoglobin, which stores oxygen.
  • Cardiac muscle is adapted to be highly resistant to fatigue.

• Anatomy of the Heart

  • The heart is a muscular organ responsible for pumping blood through the blood vessels using rhythmic contractions of cardiac muscle.
  • They are located in the left atrial wall of the heart and send nerve impulses to a large, highly specialized set of nerves called the Purkinje fibers, which in turn send those nerve impulses to the cardiac muscle tissue.
  • The middle layer of the heart is called the myocardium, and contains specialized cardiac muscle tissue responsible for contraction.
  • Cardiac muscle tissue is distinct from skeletal or smooth muscle because it pumps involuntarily based on conduction from the AV and SA nodes.
  • Note the difference in the thickness of the muscled walls of the atrium and the left and right ventricle.

• Muscle Tone

  • Muscle tone is controlled by neuronal impulses and influenced by receptors found in the muscle and tendons.
  • The main regulator of muscle tone is the muscle spindle, a small sensory unit that is closely associated with and lies parallel to a muscle.
  • If tone decreases and the muscle stretches the spindle, an impulse results in a muscle contraction.
  • Smooth and cardiac muscles do not have specialized muscle spindles.
  • Muscle tone ensures that even when at rest the muscle is at least partially contracted.

• Arrangement of Fascicles

  • Skeletal muscles are grouped into fascicles, which are bunches of muscle fibers surrounded by a perimysium.
  • Skeletal muscle tissue is composed of numerous muscle fibers which are separated from adjacent muscles and other tissues by a layer of dense, elastic connective tissue termed the fascia.
  • This fascia can project beyond the end of the muscle and attach to bones, other muscles, and other tissues.
  • The fascia surrounding a muscle or muscle group does not contain many blood vessels, but is rich with sensory receptors.
  • Whilst both cardiac and smooth muscles are also wrapped in connective tissue, they are not differentiated in the same way as skeletal muscles.