Muscular System

• Organ system


  The muscular system, in conjunction with the skeletal system, allows the movement of internal structures, limbs, and the body as a whole
• Muscles can be categorized by

  • Function (skeletal, visceral, or cardiac)
  • Activation method (voluntary or involuntary)
  • Physiology (smooth, striated or unstrained)
• Skeletal Muscles


  • Striated, voluntary muscles that are involved in the movement of the skeleton
  • Can be intentionally controlled by the animal
• Visceral Muscles


  • Smooth or visceral muscles are involuntary, unstraited muscles found in the digestive organs and blood vessels of the body
  • Function automatically and can not be controlled by the animal
• Cardiac Muscle


  • Involuntary, striated muscle found only in the heart
  • No conscious control, but can be regulated by the autonomic nervous system
• Functional groups of skeletal muscles

  • Flexors
  • Extensors
  • Abductors
  • Adductors
• When one muscle contracts (flexes or shortens)


  The other one relaxes (extends or lengthens)
• Synergists


  Muscles that work together to perform a movement
• Flexor muscles


  Decrease the angle between two lever bones when they contract
• Extensor muscles


  Increase the angle between two lever (bones) when they contract
• Abductor muscles


  Move limbs away from the median plane (the middle or main part of the body)
• Adductor muscles


  Pull limbs toward the median plane (middle or main part of the body)
• Skeletal muscle attachment


  • Most skeletal muscles attach to two different bones
  • The point of origin is on the most stable or least movable bone while the insertion point is on the more movable bone
• Structure of Skeletal Muscle

  • Made up of bundles of fibers or cells that stretch from one tendon to the other
  • Bundles of fibers lie parallel to each other within the muscle sheath making the muscle appear striped, or striated
  • Each bundle consists of fibers, which are individual cells with multiple nuclei
  • Individual muscle fibers are made up of bundles of myofibrils enclosed in a series of sarcomeres, made up of thick filaments of myosin and thin filaments of actin
• Muscle contraction


  1. Sliding-filament action

  2. Each individual sarcomere contracts as a result of the actin and myosin filaments sliding over each other
• Energy utilized for muscle contraction

  Comes primarily from non-protein sources such as adenosine triphosphate (ATP), glycogen and body fats