Musculoskeletal System

• Musculoskeletal System


  The muscular and skeletal systems work together to support and move the body
• Skeleton


  Gives the shape and form to the body and prevents soft tissues from collapsing in a heap
• Muscles


  Attached to bones are able to move them or hold them steady enabling us to stand erect, walk, run and jump
• Types of Muscle


  • Skeletal Muscle
  • Smooth Muscle
  • Cardiac Muscle
• Skeletal Muscle


  • Enable movement – contraction of skeletal muscle bring about movement at joints
  • Give body form and maintain posture
  • Under conscious control (voluntary)
  • Attached to bone
  • Striated (has striations/stripes)
• Smooth Muscle


  • Allow movement in many internal organs such as stomach and intestines
  • Not under conscious control (involuntary)
  • Non-striated
• Cardiac Muscle


  • Contracts to reduce space in chambers of the heart pushing blood out
  • Not under conscious control (involuntary)
• Properties of Muscle


  • Contractibility
  • Extensibility
  • Elasticity
  • Excitability
• Contractibility


  Ability to contract (shorten in length)
• Extensibility


  Ability to be stretched
• Elasticity


  Ability to return to original length after being stretched
• Excitability


  Ability to respond to a stimulus (nerve impulse)
• Muscle Fibre


  Elongated cylinders with many nuclei, surrounded by thin, transparent plasma membrane, sarcolemma, containing the cytoplasm, sarcoplasm
• Structure of Skeletal Muscle


  • Muscles are held together in bundles surrounded by connective tissue (perimysium)
  • Another sheath of connective tissue holds all the bundles together (epimysium)
  • Towards the end of the muscle they taper and blend to form the tendon
• Muscle Bundles (Fascicles)


  Composed of muscle cells, called muscle fibres, that lie parallel to each other
• Structure of Muscle Fibres


  • Bundles (Fascicles) of muscle fibres (cells)
  • Each of which contains 100's – 1000's of Myofibrils
  • Actin and Myosin Myofilaments
• Myofibrils


  Thread-like structures within each muscle fibre which lie parallel to each other and run the length of the fibre
• Sarcoplasmic Reticulum


  Tubular network that surrounds the myofibrils and stores calcium ions released during muscular contractions
• Myofilaments


  • Thick myofilaments, composed mainly of protein myosin
  • Thin myofilaments, composed mainly of protein actin
• Muscle Contraction


  1. Nerve impulse reaches muscle

  2. Releases Ca2+ which unblocks actin binding sites

  3. Myosin heads bind to actin

  4. Myosin head bends and pulls the actin (power stroke)

  5. Myosin head detaches from the actin with the help of energy (ATP)

  6. Myosin returns to normal position ready to re-attach to actin
• As the muscle contracts


  The actin and myosin filaments slide past one another, shortening the sarcomere
• Antagonistic Pairs


  Pairs of muscles where one produces movement in one direction while the other produces movement in the opposite direction
• Antagonistic Pairs


  • Biceps and Triceps
  • Hamstrings and Quads
• Agonist


  Muscle that causes the desired action, also called the prime mover
• Antagonist


  Muscle that has an action opposite to that of the agonist/prime mover
• Synergist


  A muscle that helps the prime mover during a particular movement
• Fixator


  A muscle that contracts to immobilize a joint
• Flexor


  Muscle that bend joints (flexion decreases the angle between articulating bones)
• Extensor


  Muscle that straighten joints (extension increases the angle between articulating bones)
• Muscle Tone


  Maintaining partial contraction of skeletal muscles
• Muscle tone holds many of our body parts in position - e.g. head held up by partial contraction of neck muscles
• Posture, the way the body is held when sitting/standing, depends on muscle tone
• Musculoskeletal structures


  • Provide framework/support for the body and give it shape
  • Protect vital organs
  • Provide attachment points for muscles
• Vital organs protected by musculoskeletal structures


  • Brain protected by skull
  • Heart, lungs and kidneys protected by ribs
  • Spinal cord protected by spinal column
• Movement production


  1. Muscle contraction

  2. Bone acts as a lever
• Sesamoid bone


  A bone that is partially wrapped in a tendon
• Some bones are classified under more than 1 category
• Bones classified under more than 1 category


  • Carpals classified as short and irregular bones
• Appendicular skeleton


  • Major role is to assist with movement
  • Includes the major limbs: arms, legs, shoulder and pelvic girdles
• Axial skeleton


  • Forms the basic central structure to support the remainder of the skeleton
  • Protects many of the vital organs: skull protects the brain, vertebrae protect the spinal cord, ribs protect the heart, lungs and kidneys