muscle contraction lec

• Amoeboid movement

  A form of movement especially characteristic of amoebas and other unicellular forms; also found in many wandering cells of metazoans, white blood cells, embryonic mesenchyme, and numerous other mobile cells that move through tissue spaces
• Cell migration in amoeba

  1. The protruding of pseudopodia driven by the aggregation and activation of the adhesion complex

  2. Formation of new adhesions driven by actin filaments

  3. Development of traction. Cell contents move forward through the contraction of the cortex at the back of the cell

  4. Release of old adhesions. The adhesive contact of the cell tail is broken by extracellular proteolytic enzymes such as MMPs to end the movement of cell crawling
• Cilia

  Minute, hair-like, motile structure that extend from surfaces of cells of many animals; functions to move unicellular organisms through their aquatic environment (e.g. paramecium) or propel fluids and materials over epithelial surfaces of larger animals (e.g. trachea of humans)
• Flagella

  A whip-like structure longer than a cilium; usually present singly or in small numbers at one end of a cell; found in many single-celled eukaryotes, in animal spermatozoa, and in sponges; function for locomotion
• Cilia and flagella have the same basic internal structure as cilia (although with several exceptions)
• Flagellum

  Beats in wavelike undulations, propelling water parallel to the main axis of itself
• Cilium

  Propels water in direction parallel to the cell surface
• Muscle movement

  Alternating contraction and relaxation of muscles
• All muscle cells are elongated (muscle) fibers
• Prefixes

  • myo and mys (muscle)
  • sarco (flesh)
• More than 700 muscles are found in the human body
• Muscles make up half of the body weight
• Myology

  The scientific study of muscles
• Three types of vertebrate muscles

  • Skeletal
  • Cardiac
  • Smooth
• Functions of Muscular Tissue

  • Producing body movements
  • Stabilizing body positions
  • Storing and moving substances within the body
  • Generating heat
• Types of Invertebrate Muscle

  • Smooth
  • Striated
  • Oblique striated
• The wings of some small flies operate at frequencies greater than 1000 beats per second
• Fibrillar muscle

  Contracts at very high frequencies and has very limited extensibility
• Tropomyosin

  A protein that winds around the chains of the actin filament and covers the myosin-binding sites to prevent actin from binding to myosin
• Troponin-tropomyosin complex

  Prevents the myosin "heads" from binding to the active sites on the actin microfilaments
• The Cross-bridge Cycle

  1. Tropomyosin has to expose the myosin-binding site on an actin filament to allow cross-bridge formation between the actin and myosin microfilaments

  2. Ca++ bind to troponin so that tropomyosin can slide away from the binding sites on the actin strands allowing the myosin heads to bind to these exposed binding sites and form cross-bridges

  3. The thin filaments are then pulled by the myosin heads to slide past the thick filaments toward the center of the sarcomere. But each head can only pull a very short distance before it has reached its limit and must be "re-cocked" before it can pull again, a step that requires ATP
• Sources of ATP

  • Creatine phosphate metabolism
  • Anaerobic glycolysis
  • Fermentation and aerobic respiration
• Creatine phosphate metabolism

  1. In a resting muscle, excess ATP transfers its energy to creatine, producing ADP and creatine phosphate

  2. When the muscle starts to contract and needs energy, creatine phosphate transfers its phosphate back to ADP to form ATP and creatine by creatine kinase

  3. Can only provide approximately 15 seconds worth of energy, at which point another energy source has to be used
• Anaerobic glycolysis

  1. Each glucose molecule produces two ATP and two molecules of pyruvic acid, which can be used in aerobic respiration or converted to lactic acid

  2. If oxygen is not available, pyruvic acid is converted to lactic acid, which may contribute to muscle fatigue during strenuous exercise when high amounts of energy are needed but oxygen cannot be sufficiently delivered to muscle
• Fermentation and aerobic respiration

  1. Aerobic respiration is the breakdown of glucose in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP

  2. Approximately 95 percent of the ATP required for resting or moderately active muscles is provided by aerobic respiration, which takes place in mitochondria
• Amoeboid movement

  A form of movement especially characteristic of amoebas and other unicellular forms; also found in many wandering cells of metazoans, white blood cells, embryonic mesenchyme, and numerous other mobile cells that move through tissue spaces
• Cell migration in amoeba

  1. The protruding of pseudopodia driven by the aggregation and activation of the adhesion complex

  2. Formation of new adhesions driven by actin filaments

  3. Development of traction. Cell contents move forward through the contraction of the cortex at the back of the cell

  4. Release of old adhesions. The adhesive contact of the cell tail is broken by extracellular proteolytic enzymes such as MMPs to end the movement of cell crawling
• Cilia

  Minute, hair-like, motile structure that extend from surfaces of cells of many animals; functions to move unicellular organisms through their aquatic environment (e.g. paramecium) or propel fluids and materials over epithelial surfaces of larger animals (e.g. trachea of humans)
• Flagella

  A whip-like structure longer than a cilium; usually present singly or in small numbers at one end of a cell; found in many single-celled eukaryotes, in animal spermatozoa, and in sponges; function for locomotion
• Cilia and flagella have the same basic internal structure as cilia (although with several exceptions)
• Flagellum

  Beats in wavelike undulations, propelling water parallel to the main axis of itself
• Cilium

  Propels water in direction parallel to the cell surface
• Muscle movement

  Alternating contraction and relaxation of muscles
• All muscle cells are elongated (muscle) fibers
• Prefixes

  • myo and mys (muscle)
  • sarco (flesh)
• More than 700 muscles are found in the human body
• Muscles make up half of the body weight
• Myology

  The scientific study of muscles
• Three types of vertebrate muscles

  • Skeletal
  • Cardiac
  • Smooth
• Muscular tissues

  • Differ from one another in their microscopic anatomy, location, and how they are controlled by the nervous and endocrine systems