Muscle organization and function

• 4 patterns of fascicle arrangements

  1. Circular
  2. Parallel
  3. Convergent
  4. Pennate
• Circular 


  Fibers arranged concentrically around an opening

  
• Parallel


  Fascicles are parallel to long axis of muscle

  • high endurance
  • not very strong

  
• Convergent


  Triangular muscle with common attachment site

  • Direction of pull of muscle can be changed

  
• Pennate


  Muscle body attached to one more tendons

  • fascicles at oblique angle to tendon
  • Most muscle fibers
  • generates the most force

  
• Exercise and skeletal muscle

  • Muscle hypertrophy: an increase in fast muscle fiber size
  • Building muscle increases fiber size but not number of fibers
  • Muscle atrophy: A wasting of muscle that reduces fiber size
  • Reduced stimulation results in reduced muscle size, tone, and power
• Muscle contraction types

  1. Concentric: muscle shortens
  2. Eccentric: muscle lengthens
  3. Isometric: muscle does not change length

  
• Actions of skeletal muscles

  • Agonist: Contraction produces the movement; also called the prime mover

  ex. The triceps brachial is the agonist for the forearm extension

  • Antagonist: A muscle whose action opposes that of an agonist

  ex. the biceps brachial is the antagonist for forearm extension; it is antagonistic to the triceps brachii

  • Synergist: A muscle that assist the agonist in performing its action
• Muscle naming


  Muscles are named according to several criteria:

  • Muscle action
  • Specific body regions
  • Muscle attachments
  • Orientation of muscle fibers
  • Muscle shape and size
  • Muscle heads/tendons of origin