Muscle Tissue Overview

Muscle Tissue Overview

• Muscle tissue is composed of elongated cells called muscle fibers (muscle cells).
• Its function is to move structures and produce contractions.
• Terminology:
  • Fiber: muscle cell
  • Myo: muscle
  • Sarco: muscle

Striated Muscle

• This category includes skeletal and cardiac muscle.

Skeletal Muscle

• Attached to at least one end of the skeleton.
• Composed of bundles of long, cylindrical, multinucleated cells (nuclei are peripheral).
• Exhibits cross-striations.
• Generates strong contractions of short duration.
• Contractions are typically under voluntary control (somatic innervation).
• Cells range up to 100µm in diameter.

Cardiac Muscle

• Constitutes most of the heart (and some walls of pulmonary veins and superior vena cava).
• Exhibits both cross-striations and intercalated discs (sites of contact between individual cardiac muscle cells).
• The cells are smaller than skeletal muscle cells (10-20µm in diameter), branched, and possess one or two nuclei located centrally.
• Produces rhythmic, strong, and continuous contractions under involuntary control (autonomic innervation).

Non-Striated Muscle

• This includes smooth muscle.

Smooth Muscle

• Composed of fusiform cells without striations.
• Arranged in sheets, forming layers in walls of tubes and hollow structures.
• Chief role involves regulating the size of lumina or cavities.
• Produces weaker contractions that can last longer.
• Contraction is involuntary (autonomic innervation).

Skeletal Muscle Organization

• Epimysium: Connective tissue surrounding the entire muscle.

  • Continuous with the tendon.

• Perimysium: Connective tissue surrounding fascicles (bundles of muscle fibers).

  • Contains larger blood vessels and nerves.

• Endomysium: Connective tissue surrounding individual muscle fibers.

  • Contains capillaries and nerve endings.
  • Similar to a basal lamina.

• Function: Transmits the pull of muscle cells to the bone (CAMs).

Organization of the Muscle

• Muscle → Fascicles → Fibers → Myofibril → Myofilaments (actin & myosin)

• The muscle fibers exhibit cross-banding (sarcomere, Z line, I band, A band, H band, M lines, desmin).

• The T-system (transverse tubules, triads, sarcoplasmic reticulum [SR]) is crucial in muscle contraction.

• Contraction control is coordinated by:

  • Motor nerve: neuromuscular junction & motor end plate
  • Sensory nerve: neuromuscular spindle

Cardiac Muscle Organization

• Contains a specialized system called the T-tubule-sarcoplasmic reticulum (SR) junction (called the triad). In the heart, it is called a diad.
• Contains a terminal cistern for storage of calcium.
• Muscle fiber organization also includes specialized intercalated discs crucial for electrical connections between cells.

Smooth Muscle Organization

• Smooth muscle cells have a different structure and specialized proteins compared to other muscle types.
• The primary features of smooth muscle are focal densities, and adhesion densities that hold the cells together during contraction.