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.

• 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.

• Energy Requirements

  • Cardiac cells contain numerous mitochondria, which enable continuous aerobic respiration and production of ATP for cardiac function.
  • Cardiac muscle tissue has among the highest energy requirements in the human body (along with the brain) and has a high level of mitochondria and a constant, rich, blood supply to support its metabolic activity.
  • Cardiac muscle cells contain larger amounts of mitochondria relative to other cells in the body, which enable higher ATP production.
  • Myoglobin transfers oxygen from the blood to the muscle cell and also stores reserve oxygen for aerobic metabolic function in the muscle cell.
  • Myoglobin provides a back-up store of oxygen to muscle cells.

• Overview of the Musculoskeletal System

  • Three types of muscle tissue exist in the body.
  • These are skeletal, smooth, and cardiac muscle.
  • Skeletal and cardiac muscles have striations that are visible under a microscope.
  • Cardiac muscles are found in the heart.
  • Cardiac and smooth muscle are characterized by involuntary movement (not under conscious control).

• 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.