muscular system

• Almost all of the 700 individual muscles that make up the muscular system, such as the biceps brachii muscle, include both skeletal muscle tissue and connective tissue

  
• Function of most muscles

  To produce movements of body parts
• Function of a few muscles

  To stabilize bones so that other skeletal muscles can execute a movement more effectively
• This chapter presents many of the major skeletal muscles in the body, most of which are found on both the right and left sides

  
• We will identify the attachment sites and innervation (the nerve or nerves that stimulate contraction) of each muscle described
• Developing a working knowledge of these key aspects of skeletal muscle anatomy will enable you to understand how normal movements occur

  
• This knowledge is especially crucial for professionals, such as those in the allied health and physical rehabilitation fields, who work with patients whose normal patterns of movement and physical mobility have been disrupted by physical trauma, surgery, or muscular paralysis
• Muscular system and muscular tissue contribute to homeostasis by

  • Stabilizing body position
  • Producing movements
  • Regulating organ volume
  • Moving substances within the body
  • Producing heat
• Lever


  A rigid structure that can move around a fixed point called a fulcrum
• Joints act as fulcrums for the levers
• Types of levers


  • First-class
  • Second-class
  • Third-class
• First-class lever


  Fulcrum is between the effort and the load
• Second-class lever


  Load is between the fulcrum and the effort
• Third-class lever


  Effort is between the fulcrum and the load
• Second-class levers always produce a mechanical advantage
• Third-class levers always produce a mechanical disadvantage
• Fascicle


  Bundles of skeletal muscle fibers (cells) within a muscle

  
• Fascicle arrangements


  • Parallel
  • Fusiform
  • Circular
  • Triangular
  • Pennate
• Prime mover (agonist)


  Muscle that contracts to cause an action
• Antagonist


  Muscle that stretches and yields to the effects of the prime mover
• If a prime mover and its antagonist contract at the same time with equal force, there will be no movement
• Sometimes a prime mover crosses other joints before it reaches the joint at which its primary action occurs
• Synergist


  Muscle that assists the prime mover
• Fixator


  Muscle that stabilizes a bone so that the prime mover can execute a movement more effectively
• Lever structure and types of levers

  • Levers are divided into three types based on the placement of the fulcrum, effort, and load (resistance)
• Resting length


  The longer the fibers in a muscle, the greater the range of motion it can produce
• Muscle power


  Depends on the total cross-sectional area, because a short fiber can contract as forcefully as a long one
• Fascicular arrangement


  Often represents a compromise between power and range of motion
• Fascicular arrangement types


  • Pennate muscles
  • Parallel muscles
• Pennate muscles


  Have a large number of short-fibered fascicles distributed over their tendons, giving them greater power but a smaller range of motion
• Parallel muscles


  Have comparatively fewer fascicles, but they have long fibers that extend the length of the muscle, giving them a greater range of motion but less power
• Coordination among muscles


  1. Flexors-extensors

  2. Abductors-adductors

  3. Synergists contract and stabilize intermediate joints

  4. Fixators steady the proximal end of a limb while movements occur at the distal end
• Compartment


  A group of skeletal muscles, their associated blood vessels, and associated nerves, all of which have a common function
• In the upper limbs, flexor compartment muscles are anterior, and extensor compartment muscles are posterior
• Sphincter


  Decreases size of an opening
• Tensor


  Makes body part rigid
• Rotator


  Rotates bone around longitudinal axis
• Biceps


  Two origins
• Triceps


  Three origins
• Quadriceps


  Four origins