MUSCLE TISSUE

• Contractility

  • ability to shorten, an inherent property of all cells
  • it is exhibited to a high degree by only a few cell; pericytes; myoepithelial cells; muscle cells (myocytes, myoid cells)
• pericytes

  • associates with very small blood vessels
• myoepithelial cells

  • which embrace the acini and small ducts of some exocrine glands
• muscle cells (myocytes; myeloid cells)

  • which exhibit greatest degree of contractility
• muscle tissue

  • like epithelium and nervous tissue
  • highly cellular tissue
  • composed of muscle cells that are supported and bound together by intercellular material that consists of connective tissue
  • basic tissue responsible for locomotion of the Individual and movement of the various parts of the body because muscle cells are highly contractile
• muscle cell contraction

  • moves or restrains the movement of a body part
• muscle cells

  • derived from mesoderm
  • elongated cells
  • often referred to as muscle fibers
  • individually enveloped by basal lamina
• ectoderm - iris
• sarcollema

  • cell membrane of muscle cells
• sacroplasm

  • cytoplasm of muscle cells
• sarcoplasmic reticulum

  • smooth-surfaced endoplasmic reticulum of muscle cells
• sarcosomes

  • mitochondria of muscle cells
• types of muscle cells (fibers)

  • skeletal muscle cell
  • smooth muscle cell
  • cardiac muscle cell
• skeletal and cardiac muscle fibers

  • striated because, in routine LM preparations, they exhibit prominent alternating light and dark cross striations
• smooth muscle cells

  • nonstriated because they do not exhibit cross striations
• skeletal muscle

  • organized to form mouse-shaped organs that are simply referred to as muscles or skeletal muscle
  • most muscles are named, e.g., pectoralis major muscle and gastrocnemius muscle.
  • muscles whose one or both ends are not attached to the skeletal system such as upper third of the esophagus and the muscles of facial expression
  • referred to as voluntary muscle
• Typically, a muscle is attached at either end by dense regular connective tissue called tendon to a part of the skeletal system (bone or cartilage).
• under voluntary movement

  • muscles of limbs
  • body wall
  • face
• not under voluntary control

  • pharynx
  • upper part of esophagus
• skeletal muscle contraction

  • is characteristically quick and forceful
• bundles of fascicles

  • collection of numerous skeletal muscle fibers bunched in groups
• epimysium

  • envelops the bundles or fascicles by tough, dense, irregular connective tissue
  • sometimes called as fascia
• perimysium

  • where each of the fascicles is likewise encased by connective tissue
  • keeps the muscle fibers within the fascicle together
  • avenue for the blood vessels and nerve fibers
• endomysium

  • where each of the muscle fibers is also individually wrapped and supported, external to their basal lamina, by a delicate connective tissue layer
  • mainly reticular fibers
• skeletal muscle

  A) fascia

  B) epimysium

  C) endomysium

  D) perimysium

  
• Skeletal Muscle Cells (Skeletal muscle fibers)

  • long, tapering, cylindrical, and multinucleated cell
  • length (<10 to 35 cm) and diameter (10 to 100 um)
  • arise in the embryo from the fusion of mononuclear muscle cell precursors called myoblasts that evidently differentiate from mesenchymal cells
  • oval nuclei (are longitudinally oriented and located in the peripheral portion of the cells, near the sarcolemma)
  • sarcoplasm - acidic
  • contains dissolves myoglobin
  • presence of numerous long but thin filamentous elements called myofibrils.
  • do not branch
  • multinucleated
  • incapable of cell division
• myoglobin

  • oxygen-binding protein responsible for the brownish color of the muscle
• myofibrils (skeletal muscle fibers)

  • length- 5,000 to 10,000 per muscle fiber
  • diameter - 1 to 2 um
  • arranged parallel to the long axis of the cell and exhibit transverse striations of alternating light and dark band
• isotropic bands (I-Bands)

  • light bands
  • do not alter polarized light
• anisotropic bands (A-bands)

  • display birefringence in polarized light
• skeletal muscle, longitudinal section

  A) perimysium

  B) fibers/cells

  C) endomysium

  D) muscle fascicle

  E) fibers/cells

  F) fibers/cells

  G) perimysium

  
• skeletal muscle, cross section

  A) perimysium

  B) perimysium

  C) perimysium

  D) perimysium

  
• Z-line (Zwischenscheiben line, -band, or -disc)

  • fine dark transverse line
  • bisects the I-band
• H-band (heller band)

  • lighter mid-portion
  • A-band
  • further bisected by a thin dark stripe, the M-line (Mittelscheibe line)
• sarcomere (skeletal muscle)

  • myofibril made up of numerous (up to 10,000) small contractile units, laid end to end
  • region that spans two Z-lines
  • 1.5 to 2 um long in a resting muscle
  • 1,000 to 2,000 of myofilaments that are arranged parallel to the long axis
• muscle filaments (myofilaments)

  • a collection of thread-like structures in sacromere
  • types: thick and thin
• thick filaments (skeletal muscle)

  • middle zone of a sarcomere
  • span the region of the A-band
  • 10 to 15 nm in diameter and 1.5 to 1.6 um in length
  • kept aligned by the attachment of their midpoints at the M-line
• thin filaments (skeletal muscle)

  • occupy the peripheral zones of a sarcomere
  • more numerous
  • 5 to 6 nm in diameter and 1.0 um in length
  • one end is attached to a Z-line while the other end is free
• resting muscle cell

  • thick and thin filaments partially overlap each other at the A-band
  • each thick filament is surrounded, in hexagonal pattern, by six thin filaments
  • central regions of A-band - thick filaments are not overlapped by the thin filaments which corresponds to the H-band
  • peripheral areas - occupied only by thin filaments which comprises the I-band
• Composition and Organization of a Myofibril

  A) myofibril

  B) sacromere

  C) myosin

  D) F-actin

  E) G-actin